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Five isolates of the bean rust fungus Uromyces appendiculatus were shown to be specifically virulent on bean genotypes of Andean origin. This specificity was demonstrated by the virulence of five pairs of isolates on a differential set of 30 Phaseolus vulgaris landraces. Each isolate pair was from a different country in the Americas and consisted of one Andean-specific isolate and one nonspecific isolate. Of the differential P. vulgaris landraces, 15 were of Middle American origin and 15 were of Andean origin. The Andean-specific rust isolates were highly virulent on Andean landraces but not on landraces of Middle American origin. Rust isolates with virulence to Middle American landraces were also generally virulent on Andean material; no truly Middle American-specific isolates were found. Random amplified polymorphic DNA (RAPD) analysis of the rust isolates also distinguished the two groups. Four of the Andean-specific rust isolates formed a distinct group compared to four of the nonspecific isolates. Two of the isolates, one from each of the two virulence groups, had intermediate RAPD banding patterns, suggesting that plasmagomy but not karyogamy occurred between isolates of the two groups.

Populations of 90 Uromyces appendiculatus isolates were collected from throughout the Americas and evaluated for virulence on 19 standard bean rust differentials, and also on 12 landraces of Phaseolus vulgaris from South and Central America. The landrace differentials represented geographical centers of bean domestication. Three groups were observed. Two groups were isolates from centers of bean domestication and a third heterogeneous group comprised isolates from countries in South and Central America. Molecular analysis using random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) was also conducted on these isolates. Cluster analysis of the molecular profiles showed three groups that corresponded to those obtained by virulence tests. These results show a clear differentiation of the pathogen population along similar lines as its host and suggest parallel evolution in the bean rust pathosystem.

Both the common bacterial blight (CBB) pathogen (Xanthomonas campestris pv. phaseoli) and X. fuscans subsp. fuscans, agent of fuscous blight, cause indistinguishable symptoms in common bean, Phaseolus vulgaris. Yield losses can exceed 40%. Lack of information about the specificity between X. campestris pv. phaseoli strains and major quantitative trait loci (QTL) or alleles conferring resistance makes the task of identifying genetic changes in host–pathogen interactions and the grouping of bacterial strains difficult. This, in turn, affects the choice of pathogen isolates used for germplasm screening and complicates breeding for CBB resistance. Common bean host genotypes carrying various sources and levels of resistance to CBB were screened with 69 X. campestris pv. phaseoli and 15 X. fuscans subsp. fuscans strains from around the world. Differential pathogenicity of the CBB pathogen was identified on the 12 selected bean genotypes. The X. fuscans subsp. fuscans strains showed greater pathogenicity than X. campestris pv. phaseoli strains having the same origin. African strains were most pathogenic. The largest variation in pathogenicity came from X. campestris pv. phaseoli strains that originated in Caribbean and South American countries. Pathogenic variation was greater within X. campestris pv. phaseoli than within X. fuscans subsp. fuscans strains. Implications for breeding for CBB resistance are discussed.

Bean rust, caused by Uromyces appendiculatus (Pers.: Pers.) Unger, is an important disease of common bean (Phaseolus vulgaris L.). A coupling-phase random amplified polymorphic DNA (RAPD) marker OAD12.550 previously was identified to be linked (no recombination) to Ur-7 of Middle American (MA) origin for specific rust resistance in the common bean cross of Great Northern (GN) 1140 x GN Nebr. #1. However, a sequence characterized amplified region (SCAR) marker for Ur-7 present in GN1140 has not been reported. Our objectives were to convert the RAPD marker OAD12.550 most tightly linked to Ur-7 to a SCAR marker SOAD12.537 for use as a marker-assisted selection tool, and survey the presence or absence of the SCAR marker SOAD12.537 in 90 MA and Andean bean genotypes for determining the genetic relationship of Ur-7 with Ur-6. The coupling-phase SCAR marker SOAD12.537 based on a specific forward (5'-AAGAGGGCGTGAGATCGTCG-3') and reverse (5'-AAGAGGGCGTCTTGAAGGTT-3') primer pair showed no recombination with Ur-7 in an F 2 population of the GN1140 x Nebr. #1 cross. The SCAR marker was also present in pinto US-5 from which the rust resistance of GN1140 was derived and in the closely related pinto US-14. The cosegregating SCAR marker identified MA pinto bean cultivars/lines Olathe, Bill Z, Apache, Montrose, BelDak-RR-1 and-2, and CO 12783 that have rust resistance gene Ur-6 and also have Ur-7, identified in earlier literature as Ur c , due to presence of the marker. Other cultivars/lines with Ur-6 such as Weihing, Burke, Kodiak, Topaz, Golden Gate Wax, BelMiNeb 1-13, BelDakMi 1-23, and other Colorado breeding lines lack Ur-7 because of absence of the SCAR marker for the MA gene. This SCAR marker linked to Ur-7 on linkage group 11 of the core P. vulgaris linkage map can identify a phenotypically hidden resistance gene, and along with markers for other rust resistance genes, can be utilized to pyramid multiple genes for more durable rust resistance.

Resistance (R) genes containing nucleotide-binding site (NBS)-leucine rich repeats (LRR) are the most prevalent types of R gene in plants. The objective of this study was to develop PCR-based R-gene analog polymorphism (RGAP) markers for common bean (Phaseolus vulgaris L). Twenty degenerate primers were designed from the conserved kinase-1a (GVGKTT) and hydrophobic domains (GLPLAL) of known NBS-LRR type R-genes and from EST databases. Sixty-six of the 100 primer combinations tested yielded polymorphism. Thirty-two RGAP markers were mapped in the BAT 93/Jalo EEP558 core mapping population for common bean. The markers mapped to 10 of 11 linkage groups with a strong tendency for clustering. In addition, the RGAP markers co-located, on six linkage groups, with 15 resistance gene analogs (RGAs) that were previously mapped in other populations of common bean. The distance between the priming sites in NBS-LRR type R-genes is around 500 bp. Of the 32 RGAP markers, 19 had sizes larger and 13 less than 500 bp. RGAP markers mapped close to known R-genes on B11, and to QTLs for resistance on B1, B2, B6, B7, B8, B10, and B11. RGAP appears to provide a useful marker technique for tagging and mapping R-genes in segregating common bean populations, discovery of candidate genes underlying resistance QTL, and future cloning of R-genes in common bean.

Common bacterial blight (CBB) caused by Xanthomonas campestris pv. phaseoli reduces common bean (Phaseolus vulgaris L.) yield and quality worldwide. Genetic resistance provides effective disease control; however, a high level of resistance is difficult to attain and does not exist in pinto bean, the most important dry bean market class in North America. Our objective was to determine if a backcross breeding approach with the aid of molecular markers linked to quantitative trait loci (QTL) for resistance to CBB in a donor parent could be used to attain higher levels of resistance to CBB in pinto bean. QTL conditioning CBB resistance from the donor parent XAN 159 were introgressed into the recurrent parent Chase using classical backcross breeding and intermittent marker-assisted selection. Chase pinto bean is moderately resistant and the breeding line XAN 159 is highly resistant to Xanthomonas campestris. Marker assays confirmed the presence of independent QTL from GN no. 1 Sel 27 and XAN 159 in advanced backcross-derived pinto bean lines with improved CBB resistance. Agronomic characteristics of Chase were fully recovered in the backcross-derived lines. An important QTL for CBB resistance from XAN 159 on linkage group B6 was not introgressed because tight linkage between this QTL and the dominant V allele that causes an unacceptable black-mottled seed coat colour pattern in pinto bean could not be broken.

Bean rust, caused by Uromyces appendiculatus (Pers.: Pers.) Unger, is a major disease of common bean (Phaseolus vulgaris L.). A recommended strategy to obtain durable rust resistance is to use molecular markers linked to rust resistance genes for pyramiding monogenic resistance genes into a single bean cultivar. However, markers tightly linked to Ur-6 of Andean origin conferring specific resistance (SR) to rust present in Olathe have not been reported. Our objectives were to identify random amplified polymorphic DNA (RAPD) markers linked to Ur-6 controlling SR to race 51 using bulked segregant analysis in an F 2 population from the Middle American (MA) common bean cross Olathe (resistant) × Nebr.#1 sel.27 (susceptible), and determine the presence or absence of these identified markers in 70 MA and Andean bean cultivars and breeding lines. A single dominant gene controlling SR to race 51 was found in the F 2 and confirmed in the F 3 . Six RAPD markers were detected in a coupling phase linkage with Ur-6. The gene was flanked by two coupling-phase markers OBC06.300 and OAG15.300 at 1.3 and 2.0 cM. Sequence characterized amplified region (SCAR) marker SOBC06.308 was developed based on the specific primer pair designed from the sequence of the RAPD marker OBC06.300. The RAPD and SCAR markers were also present in MA pinto bean germplasm having Ur-6 as well as Golden Gate Wax, another source of Ur-6. However, these markers were also present in six Andean cultivars without Ur-6, suggesting gene pool specificity. Among five repulsion-phase markers identified, OAY15.200 was the most closely linked to Ur-6 at 7.7 cM. We also confirm the Ur-6 location on linkage group 11 of the P. vulgaris map. These RAPD and SCAR markers linked to Ur-6 identified here, along with markers for other independent rust resistance genes, could be utilized to pyramid multiple genes into a bean cultivar for more durable rust resistance.

Bean rust, caused by Uromyces appendiculatus (Pers.: Pers.) Unger, is a major disease of common bean (Phaseolus vulgaris L.). A recommended strategy to obtain durable rust resistance is to use molecular markers linked to rust resistance genes for pyramiding monogenic resistance genes into a single bean cultivar. However, markers linked to the Ur-7 gene for specific resistance (SR) to rust present in the cultivar Great Northern (GN) 1140 have not been reported. Our objectives were to identify random amplified polymorphic DNA (RAPD) markers linked to the Ur-7 gene for SR to rust race 59 using bulked segregant analysis in an F 2 population from the Middle American (MA) common bean cross 'GN1140' (resistant) × GN Nebr. #1 (susceptible) and to map the Ur-7 gene on an existing RAPD marker-based linkage map constructed by means of recombinant inbred lines (RILs) from the MA cross GN BelNeb-RR-1 × A 55. A single dominant gene controlling SR to race 59 was found in the F 2 and confirmed in the F 3 . Six RAPD markers were detected in a coupling phase linkage with the Ur-7 gene. Cosegregating coupling-phase markers OAD12.550 and OAF17.900 were found. These were also present in pinto US-5 from which the rust resistance of GN1140 was derived. Among the three repulsion-phase markers, marker OAB18.650 was the most closely linked to the Ur-7 gene at a distance of 7.6 centimorgans (cM). All linked markers detected in the F 2 population also segregated in the RILs and were located on linkage group 11 of the existing linkage map. These markers linked to the Ur-7 gene of MA origin identified here, along with other independent rust resistance genes from other germplasm, could be utilized to pyramid multiple genes into a bean cultivar for more durable rust resistance.

Disease and abiotic stress are important factors limiting bean production wherever beans are grown. The development of bean cultivars having resistance to these stresses is a cost-effective and sustainable means to address these constraints. During the past 20 years, the Bean/Cowpea Collaborative Research Support Project (B/C CRSP) has supported common bean cultivar development and germplasm improvement programs in the USA and developing countries. Plant breeders have developed and released in Central America and the Caribbean bean cultivars and germplasm with one or more of the following traits; resistance to bean golden yellow mosaic virus (BGYMV), bean common mosaic necrotic virus (BCMNV), rust, web blight and common bacterial blight (CBB) and greater tolerance to high temperatures. In the highlands of Mexico and Ecuador bean cultivars with resistance to anthracnose, rust, root rots and bean common mosaic virus (BCMV), greater biological nitrogen fixation and improved adaptation to intermittent drought have been released. The bean breeding programs in East Africa have developed and released bean cultivars and germplasm with resistance to BCMNV, rust and bruchid seed weevils. Participation in the B/C CRSP has permitted USA bean breeding programs to develop and release bean cultivars and germplasm with resistance to BGYMV, BCMNV, anthracnose, rust, CBB, architectural avoidance to white mold and greater yield potential. Numerous plant breeders, plant pathologists and agronomists from developing countries have received advanced degree training in the USA, which has enhanced the capacity to develop improved bean cultivars for Latin America and Africa. The lack of sustainable seed production and delivery systems continues to limit the impact of the release of improved bean cultivars in many parts of Latin America and East Africa.

Diseases are a major constraint to production of beans in developing countries, reducing yields and seed quality. Contributing factors include poor disease management, lack of resistant cultivars, and the limited availability of certified disease-free seed. From the outset the Bean/Cowpea Collaborative Research Support Program (CRSP) has emphasized integrated disease management, and breeding for resistance to bean rust (Uromyces appendiculatus), common bacterial blight (Xanthomonas campestris (=X. axonopodis) pv. phaseoli) (CBB) and web blight (Thanatephorus cucumeris (anamorph Rhizoctonia solani)) (WB). Later in the 1990s, angular leaf spot (Phaeoisariopsis griseola) (ALS), and virus induced bean common mosaic (BCM) and bean common mosaic necrosis (BCMN) became more widespread and epidemic. The research included development of disease-resistant germplasm and studies of pathogenic variation and epidemiology. During the early 1990s bean golden yellow mosaic (BGYM), became a major disease of common bean in the Caribbean and Central America. No cultivar resistant to the gemini virus causing BGYM was available in the Dominican Republic (DR) and pesticides were used to reduce transmission of the virus by white flies (Bremisia tabaci) biotype A. A change in the bean-production system to limit reproduction of the vector through a host-free period and concentrate the bean growing season to a four month period reduced BGYM significantly. Improved resistant cultivars and disease management resulted in high yields and self-sufficiency of beans in the DR. Evidence for co-evolution of the pathogens causing ALS, CBB, and rust in the two major bean gene pools (Andean and Middle American) was found. Variation in the WB pathogen on bean indicated independent genetic populations and the presence of different anastosmosis subgroups. WB disease management practices should be designed for the sub-group of the pathogen. Seed transmission was found to be a significant source of R. solani inoculum. Specific (Ur-9 gene) and adult-plant resistance (Ur-12 gene) to rust was identified for PC-50 (Andean origin) in the DR, and the genes were mapped. A mobile rust nursery was developed to monitor races of rust in a region and assist in resistance-gene deployment in bean germplasm and varieties. DNA based diagnostic methods were developed to differentiate X. campestris pv. phaseoli from X. campestris pv. phaseoli var fuscans (prevalent in East Africa) and P. griseola isolates. DNA hybridization methods also were developed to identify BGYM and bean golden mosaic viruses. Research in USA and East Africa has helped define bean common mosaic virus (BCMV) and bean common mosaic necrotic virus (BCMNV) as separate viruses and has demonstrated that BCMNV appears to be indigenous to Africa. Serological tools were developed that assist in the detection and identification of potyviruses, BCMV and BCMNV. These tools are now used worldwide.

Bean/Cowpea Collaborative Research Support Program (B/C CRSP) scientists have successfully developed integrated consensus maps of the 11 linkage groups (LGs) in both bean (Phaseolus vulgaris L.) and cowpea (Vigna unguiculata L. Walp). The bean map is approximately 1200 cM with some 500 markers and an additional 500 markers shared with other bean maps. The cowpea map spans 2670 cM with over 400 markers. In addition to molecular markers, both maps include map locations of defense genes and phenotypic traits for disease and insect resistance, seed size, color and storage proteins, pod color and those traits associated with the domestication syndrome in bean. Since the bean and cowpea maps were developed independently, LGs with the same number probably refer to non-syntenic groups. Map locations of major resistance genes in bean are revealing gene clusters on LGs B1, B4, B7, and B11 for resistance to bean rust, anthracnose, common bacterial blight and white mold. Gene tagging and marker-assisted selection for disease resistance has progressed to a point where the indirect selection for resistance to a number of major diseases is now routine in bean breeding programs both in the US and overseas. # 2003 Elsevier Science B.V. All rights reserved.

Knowledge of the evolutionary origin and sources of pest resistance genes will facilitate gene deployment and development of crop cultivars with durable resistance. Our objective was to determine the source of common bacterial blight (CBB) resistance in the common bean Great Northern Nebraska #1 (GN#1) and GN#1 Selection 27 (GN#1 Sel 27). Several great northern cultivars including GN#1, GN#1 Sel 27, and Montana No.5 (the female parent of the common x tepary bean interspecific population from which GN #1 and GN # 1 Sel 27 were derived) and known susceptible checks were evaluated for CBB reaction in field and greenhouse environments. These genotypes and CBB resistant and susceptible tepary bean including Tepary #4, the male parent and presumed contributor of CBB resistance toGN#1 and GN#1 Sel 27, were assayed for presence or absence of three SCAR markers tightly linked with independent QTLs conditioning CBB resistance. The parents and F2 of Montana No. 5/GN #1 Sel 27 and Montana No.5/Othello(CBB susceptible) were screened for CBB reaction and SCAR markers. CBB resistance in Montana No.5 was comparable to that of GN#1 and GN#1 Sel27. The SAP6 SCAR marker present in GN#1 and GN#1 Sel 27 was also present in Montana No.5, and it co-segregated (R 2 =35%) with the CBB resistance in the Montana No.5/Othello F2 population. Although a few CBB resistant and susceptible transgressive segregants were found in the F2 of MontanaNo.5/GN #1 Sel 27 and later confirmed by F3 progeny tests, SAP6 SCAR marker was present in all progenies. None of the tepary bean specific CBB resistance-linked SCAR markers were present in GN#1, GN#1 Sel 27, or Montana No.5. A cluster analysis of 169 polymorphic PCR-based markers across three common bean and Tepary #4 indicated that GN#1, GN#1 Sel 27, and Montana No.5 were closely related, and not related at all with Tepary #4.Thus, these results clearly indicate Montana No.5, not Tepary #4, as the source of CBB resistance in GN#1 and GN#1 Sel 27.

Expression of lactoferrin (LF) gene, a cationic iron-binding glycoprotein, was investigated in transgenic tomato plants (Lycopersicon esculentum Mill.). Resistance of the transgenic tomato plants to the pathogen (Ralstonia solanacearum Smith) causing bacterial wilt was also determined. Tomato line F7926-96, susceptible to bacterial wilt, was transformed with Agrobacterium strain C58C1 containing a plasmid construction carrying a modified LF cDNA. The introgression of LF cDNA into the susceptible tomato line was confirmed by Southern blot and the expression of full-length lactoferrin transcript and protein was also detected by northern and western blots, respectively. Based on resistance to kanamycin, a Mendelian segregation for a single locus insertion was observed in the T1 and T2 generations and all T1 and T2 plants resistant to kanamycin showed the single corresponding band of LF cDNA in Southern blot analysis. Two transgenic tomato lines inoculated with 1 × 107 and 1 × 108 colony-forming units (CFU)/mL with Rs isolate NC251 (K60, race 1) exhibited early resistance and subsequent susceptibility, while 44% to 55% of plants survived until maturity (fruit ripening) when inoculated with 1 × 105 CFU/mL in comparison with the fully susceptible tomato line. The latter resistance to bacterial wilt in transgenic tomatoes with the stable Mendelian segregation patterns for the LF gene suggests a potential new approach to consider for control of bacterial wilt of tomato. The possible value of this gene along with other plant genes to control bacterial pathogens is discussed.

Fusarium oxysporum Schlectend. Fr. f. sp. phaseoli J.B. Kendrick and W.C. Snyder (FOP) is a vascular pathogen that causes Fusarium wilt in common bean (Phaseolus vulgaris L.). This disease is an increasing problem in the western U.S., and exploitation of genetic resistance is considered the most feasible control method. The objective of this study was to detect quantitative trait loci (QTL) for Fusarium wilt resistance in a population derived from an interracial cross between FOP-susceptible Belneb RR-1 (race Durango) x FOP-resistant A55 (race Mesoamerica). Seventy-six F 6 -derived recombinant inbred lines (RILs) were screened for disease severity in greenhouse inoculations and rated on a scale of 1 (resistant) to 9 (susceptible). The phenotypic data were compared to existing random amplified polymorphic DNA (RAPD) marker data using single-factor analysis of variance. Marker U20.750 on linkage group (LG) 10 accounted for 63.5% of the phenotypic variance for this trait. Lines exhibiting the A55 banding pattern at this locus had disease severity scores that averaged 3.6 points lower than lines with the Belneb RR-1 pattern. Two additional markers, AD4.450 on LG 3 and K10.700 on LG 11, were significant (P < 0.01) in single-factor analysis of variance, but only marker U20.750 on LG 10 remained significant when composite interval mapping (CIM) was conducted. The tight linkage between the putative QTL and U20.750, as indicated by CIM, makes this marker a promising candidate for conversion to a sequence-characterized amplified region (SCAR) for use in marker-assisted selection in Fusarium wilt resistant common bean cultivar development.

White mold (WM), incited by Sclerotinia sclerotiorum (Lib.) de Bary, is a serious disease of common bean (Phaseolus vulgaris L.). However, plant breeders have had very limited success in developing resistant (R) cultivars. Molecular markers linked to genes for R to WM may improve selection for R. The objective was to identify random amplified polymorphic DNA (RAPD) markers linked to quantitative trait loci (QTL) for partial physiological resistance (PPR), partial field resistance (PFR), porosity over the furrow (POF), and plant height (PH) in a linkage map by means of recombinant inbred lines (RILs) from the cross 'PC-50' (R) x XAN-159 (susceptible). The parents and RILs were inoculated in two separate greenhouse experiments for each isolate and were also infected naturally in the field. Significant correlations (0.39, 0.47) were found for the WM reactions in the greenhouse and field. Nine candidate QTL were found affecting PPR isolate 152 (comparison-wise P < 0.05) with strong evidence (genome-wise P < 0.01) for three QTL on linkage groups (LGs) 4, 7, and 8, based on composite interval mapping analysis. Candidate QTL affecting PPR to isolate 279 were found on LGs 2, 3, 4, 7, and 8 with very strong evidence (genome-wise P < 0.001) for a QTL linked to the C locus for seedcoat pattern. Seven candidate QTL for PFR were observed on LGs 4, 7, 8, and 11. Six of the seven candidate QTL for PFR were found in the same locations as QTL for PPR. However, two of the seven genomic regions were associated with PFR and POF that may contribute to disease avoidance.

Our objective was to identify quantitative trait loci (QTL) for seed weight, length, and height segregating in a recombinant inbred line population derived from the common bean (Phaseolus vulgaris L.) cross `PC-50' × XAN-159. The parents and progeny were grown in two separate greenhouse experiments in Nebraska, and in field plots in the Dominican Republic and Wisconsin. Data analysis was done for individual environments separately and on the mean over all environments. A simple linear regression analysis of all data indicated that most QTL appeared to be detected in the mean environment. Based on these results, composite interval mapping (CIM) analysis was applied to the means over environments. For seed weight, strong evidence was indicated for five QTL on common bean linkage groups (LGs) 3, 4, 6, 7, and 8. Multiple regression analysis (MRA) indicated that these QTL explained 44% of the phenotypic variation for the trait. Weaker evidence was found for three additional candidate QTL on bean LGs 4, 5, and 8. All eight markers associated with these QTL were significant in a MRA where the full model explained 63% of the variation among seed weight means. For seed length, CIM results indicated strong evidence for three QTL on LG 8 and one on LG 2. Three additional putative QTL were detected on LGs 3, 4, and 11. The markers associated with the three seed length QTL on LG 8, and the QTL on LGs 2 and 11 were significant in a MRA with the full model explaining 48% of the variation among seed length means. For seed height, three QTL on LGs 4, 6, and 11 explained 36% of the phenotypic variation for trait means. Four of the seven QTL for seed length and two of three QTL for seed height also appeared to correspond to QTL for seed weight. Four QTL for common bacterial blight resistance [Xanthomonas campestris pv. phaseoli (Smith Dye)] and for smaller seed size were associated on LGs 6, 7, and 8. The implications of these findings for breeders is discussed.

Diseases of beans (Phaseolus vulgaris L.) are primary constraints affecting bean production. Information on tagging and mapping of genes for disease resistance is expected to be useful to breeders. The objectives of this study were to develop a random amplified polymorphic DNA (RAPD) marker linkage map using 78 F9 recombinant inbred (RI) lines derived from a Middle-American common bean cross Great Northern Belneb RR-1 [resistant to common bacterial blight (CBB) and halo blight (HB)] × black A 55 [dominant I gene resistance to bean common mosaic potyvirus] and to map genes or QTL (quantitative trait loci) for resistance to CBB, HB, BCMV (bean common mosaic virus), and BCMNV (bean common mosaic necrosis virus) diseases. The RI lines were evaluated for resistance to leaf and pod reactions to Xanthomonas campestris pv. phaseoli (Xcp) (Smith Dye) strain EK-11, leaf reactions to two Pseudomonas syringae pv. phaseolicola (Psp) (Burkholder) Young et al. (1978) strains HB16 and 83-Sc2A, and BCMV strain US-5 and BCMNV strain NL-3. The linkage map spanned 755 cM, including 90 markers consisting of 87 RAPD markers, one sequence characterized amplified region (SCAR), the I gene, and a gene for hypersensitive resistance to HB 83-Sc2A. These were grouped into 11 linkage groups (LG) corresponding to the 11 linkage groups in the common bean integrated genetic map. A major gene and QTL for leaf resistance to HB were mapped for the first time. Three QTL for leaf reactions to HB16 were found on linkage groups 3, 5, and 10. Four regions on linkage groups 2, 4, 5, and 9, were significantly associated with leaf reactions to HB strain 83-Sc2A. The gene controlling the hypersensitive reaction to HB 83-Sc2A mapped to the same region as the QTL on LG 4. The I locus for resistance to BCMV and BCMNV was mapped to LG 2 at about 1.4 cM from RAPD marker A10.1750. Five and four markers were significantly associated with QTL for resistance to CBB in leaves and pods, respectively, with four of them associated with resistance in both plant organs. A marker locus was discovered on LG 10, W10.550, which could account for 44% and 41% of the phenotypic variation for CBB resistance in leaves and pods, respectively. QTL for resistance in pod to CBB, leaf resistance to HB, and the I gene were linked on LG 2.

Common bacterial blight (CBB), incited by the bacterial pathogen Xanthomonas campestris pv. phaseoli (Smith) Dye (Xcp) is a major problem in bean (Phaseolus vulgaris L.) producing areas worldwide. Using 128 recombinant inbred (RI) lines derived from the common bean cross BAC 6 × HT 7719, RAPD marker locus-QTL associations were previously described for resistance to two Xcp strains, EK-11 and Epif-IV. The objective of this research was to test these candidate marker locus-QTL associations in three previously untested genetic populations. In addition, RAPD marker locus-QTL associations were also investigated for resistance to a third Xcp strain, DR-7, in the first trifoliolate leaves in the original BAC 6 X HT 7719 population. The three genomic regions most significantly associated with CBB resistance in the original BAC 6 × HT 7719 population were significantly associated with CBB resistance in at least two of the three additional populations. The unmapped marker, BC409.1250, was significantly associated with CBB resistance in all four populations and all three Xcp strains, suggesting that this marker might be tightly linked to genes for CBB resistance. The RAPD marker BC409.1250 was converted into a marker that is a robust and reliable PCR-based marker. Since similar genomic regions were fond for resistance to three different Xcp strains, these QTL may be useful for breeding cultivars with a broad range of resistance.

ADDITIONAL INDEX WORDS. Phaseolus vulgaris, Xanthomonas campestris pv. phaseoli, flower color, randomly amplified polymorphic DNA (RAPD) markers, quantitative trait loci (QTL) ABSTRACT. Common bacterial blight, incited by Xanthomonas campestris pv. phaseoli (Xcp), is a serious disease of common bean (Phaseolus vulgaris L.). Randomly amplified polymorphic DNA (RAPD) markers and flower color (V gene) previously were reported to be associated with six quantitative trait loci (QTL) affecting leaf and pod resistance to Xcp. However, the markers for the QTL were not confirmed in different populations and environments to indicate their merit in breeding. The objective was to determine if the associations of RAPD markers and the V gene with QTL for leaf and pod resistance to Xcp in a recombinant inbred (RI) backcross population from the cross BC 2F6 'PC-50' x XAN-159 and for leaf resistance to Xcp in an F2 population from a different cross pinto 'Chase' x XAN-159 could be confirmed. One or two genes from XAN-159 controlled leaf and pod resistance to Xcp. Among six QTL previously detected, five in the RI backcross population and three in the F 2 population were confirmed to be associated with resistance to Xcp. The V gene and RAPD marker BC437.1050 on linkage group 5 were most consistently associated with leaf and pod resistance to two to five Xcp strains in the RI backcross population and with leaf resistance to two Xcp strains in the F 2 population. One to three QTL affecting leaf and pod resistance to Xcp accounted for 22% to 61% of the phenotypic variation. Gene number (one to two) estimations and number of QTL (one to three) detected for leaf and pod resistance to Xcp in the RI backcross population were generally in agreement. The marker BC437.1050 and V gene, along with other resistance genes from other germplasm, could be utilized to pyramid the different genes into a susceptible or partially resistant bean line or cultivar to enhance the level of resistance to Xcp. The expression of QTL may differ over environments or populations in various crops. Among 29 QTL affecting fruit size, soluble solids concentration or pH in a tomato cross, only four QTL were expressed in three environments and 10 QTL were expressed in two environments (Paterson et al., 1991). Of seven QTL for seed size found in a common bean population, only one QTL was expressed in three environments and two QTL were expressed in two environments (Park et al., 1999). No common genomic region associated with QTL affecting plant height was found in four maize populations (Beavis et al., 1991). Only one QTL affecting resistance to Xcp was consistently expressed in four common bean populations (Jung et al., 1999). These are examples of genotype × environment interaction and genetic background affecting QTL expression. Identifying markers asso- ciated with QTL based on one environment and one population may be erroneous, especially QTL with minor effects (Beavis et al., 1991; Paterson et al., 1991). In a recombinant inbred (RI) population derived from the common bean cross BAC 6 x HT 7719, RAPD markers were associated with nine QTL affecting resistance to Xcp on a linkage map (Jung et al., 1996). When these RAPD markers were tested for confirmation in other common bean populations, only three QTL affecting resistance to Xcp in three plant organs, with two Xcp strains, and in three populations were consistently confirmed (Jung et al., 1999). The results show the importance of confirmation of the marker-QTL associations in a breeding program, particularly for traits like CBB resistance that have complex inheritance patterns, low narrow-sense herita- bilities, and a number of genes involved. Flower color (V gene) and RAPD markers were associated with six QTL affecting leaf and pod resistance to Xcp in a RI population (70 F6 lines) from the cross 'PC-50' x XAN-159 in greenhouse experiments (Jung et al., 1997). However, these marker-QTL associations have not been confirmed in other populations of the same cross and or a different cross, in different Common bacterial blight (CBB), caused by Xanthomonas campestris pv. phaseoli (Xcp), is an important seed-transmitted disease in common bean (Phaseolus vulgaris L.) (Saettler, 1989). Resistant common bean cultivars are the most effective and economical strategy to control this disease (Schwartz and Galvez, 1981). Leaf, pod, and seed reactions to Xcp in some bean crosses show quantitative inheritance (Ariyarathne, 1994; Aggour and Coyne, 1989; Arnaud-Santana et al., 1994). Varying numbers of genes control leaf and or pod reactions to Xcp in different crosses and populations (Eskridge and Coyne, 1996; Silva et al., 1989). Leaf and pod reactions to Xcp in different common bean popula- tions have shown no (Coyne and Schuster, 1983; Aggour and Coyne, 1989), low (Arnaud-Santana et al., 1994), and intermedi- ate to high correlations (Ariyarathne, 1994; Rava et al., 1987). Molecular markers associated with resistance to Xcp in com- mon beans have been reported in several studies. Restriction fragment length polymorphism (RFLP) markers (Nodari et al., 1993) and randomly amplified polymorphic DNA (RAPD) mark- ers (Jung et al., 1996, 1997) associated with quantitative trait loci (QTL) affecting resistance to Xcp were reported in three linkage maps. RAPD markers associated with QTL affecting resistance to Xcp were detected using bulked segregant analysis (Miklas et al., 1996; Bai et al., 1997). Recently, RFLP markers linked to genes for resistance to Xcp were also detected (Yu et al., 1998).

Bulked segregant analysis was utilized to identify random amplified polymorphic DNA (RAPD) markers linked to genes for specific resistance to a rust pathotype and indeterminate growth habit in an F2 population from the common bean cross PC-50 (resistant to rust and determinate growth habit) × Chichara 83-109 (susceptible to rust and indeterminate growth habit). Six RAPD markers were mapped in a coupling phase linkage with the gene ( Ur-9) for specific rust resistance. The linkage group spanned a distance of 41 cM. A RAPD marker OA4.1050 was the most closely linked to the Ur-9 gene at a distance of 8.6 cM. Twenty-eight RAPD markers were mapped in a coupling phase linkage with the gene ( Fin) for indeterminate growth habit. The linkage group spanned a distance of 77 cM. RAPD markers OQ3.450 and OA17.600 were linked to the Fin allele as flanking markers at a distance of 1.2 cM and 3.8 cM, respectively. The RAPD markers linked to the gene for specific rust resistance of Andean origin detected here, along with other independent rust resistance genes from other germplasm, could be utilized to pyramid the different genes into a bean cultivar for durable rust resistance.

Great northern common bean (Phaseolus vulgaris L.) germplasm line ABC-Weihing (Reg. No. GP-246, PI 647964) was developed by the University of Nebraska Agricultural Research Division in cooperation with USDA-ARS and released in 2006. This line, tested as NE1-05-4, was bred specifi cally for enhanced resistance to common bacterial blight (CBB), a major seed borne disease of common bean caused by the bacterium Xanthomonas campestris pv. phaseoli (Smith) Dye (Xcp). ABC-Weihing is a great northern BC 5 F 3:6 line obtained from fi ve backcrosses ('Weihing'*5//'Chase'/XAN 159). The fi rst cross was made in spring 1997. Only BC n F 1 plants resistant to Xcp isolates Dominican Republic DR-7 and Nebraska SC4A, as determined by multiple needle leaf inoculation tests in the greenhouse, were used for successive backcrossing. In addition to phenotypic selection for CBB resistance, marker-assisted selection for the resistant QTL- linked marker SU91 was conducted in the BC 1 F 1 , BC 2 F 1 , and ABC-Weihing. When inoculated with Nebraska Xcp strains in the fi eld, ABC-Weihing exhibited resistance in both 2005 and 2006. ABC-Weihing has Ur-3 and Ur-6 genes for resistance to common bean rust and carries the single dominant hypersensitive I gene that provides resistance to all non-necrotic strains of the Bean common mosaic virus (BCMV). ABC-Weihing has bright white seed, blooms 45 d after planting, and is a midseason bean maturing 92 d after planting.

Breeding for resistance is an important strategy to manage common bacterial blight disease caused by Xanthomonas campestris pv. phaseoli (E. Smith) Dye (Xep) in common bean (Phaseolus vulgaris L.). It is necessary to determine if prior inoculation of the first trifoliolate leaf with Xcp influences subsequent reactions in other plant organs by increasing or decreasing resistance to Xcp. It is difficult to get an accurate estimate of heritability of disease reaction in pods since environment greatly affects the heritability estimate if flowering occurs over extended time periods. Thus, the disease reaction in attached pods versus detached pods was compared. A split-split plot design with two replications (growth chambers as blocks) was used, with bean lines as the whole-plot factors, Xcp strains as subplot factors, and bacterial inoculation treatments for leaf reactions or pod treatments as split-split plot factors. The first trifoliolate leaves, later developed leaves, and attached and detached pods were inoculated. No effects of prior inoculation on the disease reactions of subsequently inoculated leaves and pods were observed, indicating that the different plant organs can be inoculated at different times. The fact that detached and attached pods showed similar disease symptoms would suggest use of the former to reduce environment variance and improve heritability estimates of resistance.

Dry bean (Phaseolus vulgaris L.) production is limited by bean rust [Uromyces appendiculatus (Pers.) Unger var. appendiculatus]. An effective control strategy for this disease is to breed cultivars with durable resistance. Information on the inheritance, genetic relationships, and mapping of genes with molecular markers for specific resistance (SR), adult plant resistance (APR), and abaxial leaf pubescence (ALP) is needed to pyramid the desired genes for durable resistance. ALP was found to be associated previously with APR in Andean germplasm. The objective here was to identify and map RAPD markers for the genes controlling SR, APR, and ALP and to examine their relationships. Five rust pathotypes were inoculated on the unifoliate leaves of 68 recombinant inbred (RI) lines derived from `PC-50' (presence of SR, APR, and ALP) × XAN-159 (absence of SR, APR, and ALP). SR was determined by a single major gene (Ur-9) to the five rust pathotypes with no detection of recombinants. The fourth trifoliolate leaves were inoculated with one pathotype (A88T1-4b). A single major gene Ur-12 controlled APR to that pathotype. The Ur-9 gene (SR) was independent of and epistatic to the Ur-12 gene (APR). Because of the low number of APR lines in the RI population resulting from the elimination of RI lines with SR, an F2 population was developed from a cross of two homozygous RI lines selected for unifoliate susceptibility to pathotype A88T1-4b and for resistance and susceptibility of the fourth trifoliolate leaves to tag RAPD markers linked to the Ur-12 gene (APR). The single major gene Pu-a determinated ALP and was not linked to Ur-9 (SR) and Ur-12 (ALP). The gene Ur-9 (SR) was linked to RAPD marker J13-1100 at 5 cM and was not assigned to any linkage group or other markers. The gene Pu-a (ALP) was mapped at 20.2 cM from 116.500 and 3.9 cM from marker G3.1150 in linkage group 3. The Ur-12 gene (APR) was mapped at 34.6 cM from marker O13.1350 in linkage group 4b. This is the first report of mapping a gene for APR in common bean.

Zhang, Z., Coyne, D. P., Vidaver, A. K., and Mitra, A. 1998. Expression of human lactoferrin cDNA confers resistance to Ralstonia solanacearum in transgenic tobacco plants. Phytopathology 88:730-734. A construct containing a human lactoferrin cDNA was used to transform tobacco (Nicotiana tabacum) using an Agrobacterium-mediated DNA-transfer system to express this human protein in transgenic plants. Transformants were analyzed by Southern, Northern, and Western blots to determine integration of the cDNA into the plant genome and lactoferrin gene expression levels. Most transgenic plants demonstrated significant delays of bacterial wilt symptoms when inoculated with the bacterial pathogen Ralstonia solanacearum. Quantification of the expressed lactoferrin protein by enzyme-linked immunosorbent assay in transgenic plants indicated a significant positive relationship between lactoferrin gene expression levels and levels of disease resistance. Incorporation of the lactoferrin gene into crop plants may enhance resistance to other phytopathogenic bacteria as well.

Common bacterial blight (CBB), incited by Xanthomonas campestris pv. phaseoli (Xcp), is an important seed-transmitted disease of common bean (Phaseolus vulgaris L.). Tepary bean (Phaseolus acutifolius A. Gray) has high resistance to Xcp. The objective of this study was to identify RAPD markers linked to genes controlling resistance to three isolates of Xcp using bulked segregant analysis in an F2 population from the tepary bean cross CIAT-G40005 (resistant to Xcp) × Nebr.#4B (susceptible to Xcp). Twelve RAPD markers were mapped in a coupling-phase linkage with three genes for resistance to Xcp. The linkage group spanned a distance of 19.2 cM. A marker L7750 was linked to the genes for resistance to Xcp strains EK-11 and LB-2 at 8.4 cM and 2.4 cM, respectively. Markers U10400 and Y14600 were detected as flanking markers for the resistance gene to Xcp strain SC-4A at 2.4 cM and 7.2 cM, respectively. The symbols Xcp-1, Xcp-2, and Xcp-3 were assigned for the genes for resistance to Xcp strains EK-11, LB-2, and SC-4A, respectively. RAPD markers linked to the genes for resistance to Xcp could be used for transferring all of the resistance genes from P. acutifolius to a susceptible P. vulgaris cultivar.

Randomly amplified polymorphic DNA (RAPD) molecular markers were used to construct a partial genetic linkage map in a recombinant inbred population derived from the common bean (Phaseolus vulgaris L.) cross PC-50 × XAN-159 for studying the genetics of bacterial disease resistance in common bean. The linkage map spanned 426 cM and included 168 RAPD markers and 2 classical markers with 11 unassigned markers. The seventy recombinant inbred lines were evaluated for resistance to two strains of common bacterial blight [Xanthomonas campestris pv. phaseoli (Smith) Dye] (Xcp). Common bacterial blight (CBB) resistance was evaluated for Xcp strain EK-11 in later-developed trifoliolate leaves and for Xcp strains, DR-7 and EK-11, in first trifoliolate leaves, seeds, and pods. One to four quantitative trait loci (QTLs) accounted for 18% to 53% of the phenotypic variation for traits. Most significant effects for CBB resistance were associated with one chromosomal region on linkage group 5 and with two regions on linkage group 1, of the partial linkage map. The chromosomal region (a 13-cM interval) in linkage group 5 was significantly associated with resistance to Xcp strains DR-7 and EK-11 in leaves, pods, and seeds. The regions in linkage group 1 were also significantly associated with resistance to both Xcp strains in more than one plant organ. In addition, a seedcoat pattern gene (C) and a flower color gene (vlae) were mapped in linkage groups 1 and 5, respectively, of the partial linkage map. The V locus was found to be linked to a QTL with a major effect on CBB resistance.

Factors influencing Agrobacterium tumefaciens-mediated transformation of common beans (Phaseolus vulgaris L.) were examined using an intron-containing β-glucuronidase (GUS) gene as a reporter system to develop a repeatable transformation protocol. Tissue culture procedures used were based on direct shoot organogenesis. Two A. tumefaciens strains—A2760 and EHA105—were used, with emphasis on the former due to its overall higher infection rate. Eleven common-bean genotypes were compared for susceptibility to strain A2760 or EHA105. The pinto bean `Othello' was used extensively in testing different transformation conditions. Factors significantly affecting transformation rate were Agrobacterium × host interactions, explant maturity, preculture and cocultivation conditions, and selection schemes, based on transient GUS gene expression. The best transformation conditions were the use of susceptible genotypes and explants derived from mature seeds, preconditioning of explants in a medium containing 20 μmol of benzyladenine (BA) in darkness or on a filter paper, dipping explants in high concentrations of Agrobacterium cell suspension (OD650 = 0.8-1.0) followed by a long-term (6-day) cocultivation period on a semisolid agar medium in the presence of cytokinin or 3-day cocultivation on a moistened filter paper, and the use of lethal levels of selective agents. About 4% of explants, or 14% of regenerated shoots or buds, were putatively transgenic, as indicated by GUS blue staining throughout the entire shoot or bud, after explants were transformed with Agrobacterium strain A2760 using an optimized protocol.

Random amplified polymorphic DNA (RAPD) markers were used to construct a partial linkage map in a recombinant inbred population derived from the common bean (Phaseolus vulgaris L.) cross BAC 6 x HT 7719 for studying the genetics of disease resistance in common bean. The linkage map spanned 545 cM and included 75 of 84 markers used in this study. The population of 128 recombinant inbred lines was evaluated for resistance to common bacterial blight, foliar resistance to web blight (WB; Thanatephorus cucumeris (Frank) Donk), and resistance to rust ( Uromyces appendiculatus var. appendiculatus (Pers.:Pers) Unger). Common bacterial blight (CBB; Xanthomonas campestris pv. phaseoli (Smith) Dye) resistance was evaluated for CBB strain Epif-IV in later-developed trifoliolate leaves and for CBB strain EK-11 in seeds, first trifoliolate leaves, later-developed trifoliolate leaves, and pods. In addition, lines were rated for plant uprightness and branch density. Two to six markers accounted for 14% to 34% of the phenotypic variation for each trait. Significant marker locus- trait associations were found for 14 mapped loci and 7 of the 9 unmapped markers. The distribution of detected QTL appeared to be nonrandom with most significant markers associated with more than one trait or closely linked to markers significantly associated with variation for a different trait. One marker, BC409 1250 , was significantly associated with WB resistance, resistance for CBB strain Epif-IV in later-developed trifoliolate leaves, and resistance for CBB strain EK-11 in first trifoliolate leaves, later-developed trifoliolate leaves, and pods. A rust resistance gene was mapped in an interval 14.6 cM from RAPD marker H19 1050 and 12.5 cM from marker AJ16 250 . Common bacterial blight (CBB; Xanthomonas campestris pv. phaseoli), web blight (WB; Thanatephorus cucumeris), and rust (Uromyces appendiculatus var. appendiculatus) are important diseases of common bean (Harter and Zaumeyer, 1944). These diseases cause economic losses due to a reduction in seed yield and seed quality in dry bean producing regions worldwide (Galvez et al., 1989; Saettler, 1989; Stavely and Pastor-Corrales, 1989). The most reliable and effective control strategy for these diseases is the

Se estudió la herencia del número de días a la primera flor y la reacción a la bacteriosis común usando padres y generaciones F2 derivadas de los cruces 'Constanza' x GN 'Tara' e 'Iguacu' x PI207262. Un gen mayor determinó el número de días a floración en ambos cruces, en Scottsbluff, NE, en 1983 y en Lincoln, NE, en 1984. La floración tardía fue dominante en el primer cruce, mientras la floración temprana fue dominante en el segundo cruce. La misma población F2 del segundo cruce sembrada en Lincoln, en 1983, exhibió una distribución continua para el mismo carácter. Se estimó una heredabilidad en el "sentido estrecho" de 22% para el tiempo a floración. Los padres y sus progenies se inocularon, con tres aislamientos de Xanthomonas campestris pv phaseoli. En ambos cruces la reacción al patógeno se heredó cuantitativamente. Se observaron dominancias altas y moderadas para susceptibilidad en las dos poblaciones. Se estimaron valores de heredabilidad en el "sentido estrecho" de 11 y 10% en el cruce Iguacu x PI207262 para dos de los aislamientos bacterianos. Se observó una asociación significativa positiva entre la reacción al patógeno y el número de días a floración en el cruce Constanza x GN Tara.

The potato leafhopper (PLH), Empoasca fabae Harris is the most important Empoasca species attacking dry beans (Phaseolus vulgaris L.) in North America. The objective of this study was to determine the heritability (h2) of PLH injury based on parent-offspring regression analysis of F3 means on individual F2 plants derived from crosses of pinto `Sierra' (resistant) × great northern `Starlight' (susceptible), and black bean `Tacarigua' (resistant) × `Starlight' (susceptible). Low narrow-sense heritability values of 0.29 ± 0.06 and 0.28 ± 0.10, respectively, were obtained for the above crosses. The low narrow-sense heritability estimates indicated large environmental effects on the expression of PLH injury in dry beans. An allelic test showed that both resistant parents possessed the same genes for resistance.

Differences in potato leafhopper (Empoasca fubae Harris) injury symptoms were noted in 22 cultivars or lines of dry beans (Phaseolus vulgaris L.) in a 1991 field trial at North Platte, Neb. Seed yield, biomass, and plant injury symptoms were recorded. The same 22 dry bean cultivars or lines were planted in a split-plot design, with main plots protected (sprayed with insecticide) vs. unprotected (not sprayed) and cultivars or lines as subplots in 1992 and 1993. Significant differences were observed between cultivars/lines for leafhopper injury and yield in all 3 years. `Tacaragua' (black-seeded) and pinto `Sierra' were highly resistant to leafhoppers, with no visual leafhopper injury symptoms in all 3 years. Significant negative correlation coefficients between leafhopper injury symptoms and yield were recorded in the protected (4.50) and unprotected (-0.33) plots in 1993 but only in the unprotected (-0.46) plots in 1992. A cultivar x spray interaction response to leafhoppers occurred in 1992 but not in 1993. The degree of leafhopper injury symptoms varied between years.

In semiarid regions, wetness of leaves or other plant parts is essential for development of white mold disease [caused by Sclerotinia sclerotiorum (Lib.) de Bary] in dry edible bean (Phaseolus vulgaris L.). Our goal was to monitor leaf wetness in field plots and predict leaf wetness from prevailing meteorological conditions. The dew point within the canopy and the adjacent leaf temperature (infrared) were used to estimate leaf wetness in two dry bean cultivars of highly contrasting canopy architecture. These are simple, direct measurements that do not disturb the canopy. Sensors were calibrated before and after field measurement periods. Results were compared with the saturation air vapor pressure deficit from a nearby weather station to derive an empirical equation for estimating leaf wetness. The measured leaf wetness period in the dense canopy (cv. Tara) exceeded that in the open canopy (cv. Starlight) by 14% (plus an offset of 1.35 h). This corresponded to higher white mold disease (WM) severity in the dense than in the open canopy. The respective WM severity for dense and open canopies was 93 and 32% in 1990, and 73 and 10% in 1991. The empirical relationship for estimating hourly leaf wetness explained 81% of the variance in the open canopy and 70% of the variance in the dense canopy in 1991; in 1992, accuracy approached 90%. Thus, nearby weather station data offer input to a method that in turn offers a means of assessing leaf wetness in Tara and Starlight, with potential for use with other cultivars. Theoretical considerations indicate that the empirical coefficients are a function of canopy microclimate. Further studies should evaluate the relationship between these empirical coefficients and canopy architecture.

The heritability of leaf, pod, and seed reactions; stem color and abaxial leaf pubescence; and the association of these traits were studied in advanced dry bean recombinant inbred lines derived from the Phaseolus vulgaris crosses 'PC-SO' × XAN-159, 'PC-50' × BAC-6, and 'Venezuela 44' × BAC-6. The reaction to Xcp was quantitatively inherited in all three plant organs. Qualitative inheritance was found for stem color and leaf pubescence. Low to intermediate heritability values were obtained for the leaf and seed reactions to Xcp. Heritability estimates were consistently low for the pod reaction to Xcp. Low nonsignificant Pearson correlations were detected between leaf and pod reactions, leaf and seed reactions, and pod and seed reactions, except for the latter two correlations, which were low and significant in lines from the cross 'PC-50' × XAN-154. Genetic correlations between leaf and pod reactions and leaf and seed reactions were low and significant in lines from all crosses, except for Venezuela 44 × BAC-6 in the latter case. Genetic correlations between pod and seed reactions were low and nonsignificant, except in the cross 'PC-50' × XAN-159, for which a low significant correlation was observed. No significant association was found between Xcp leaf reaction and stem color or leaf pubescence. A breeding strategy for improving resistance to Xcp in P. vulgaris is discussed. Common blight (CB), caused by Xanthomonas campestris pv. phaseoli (Smith) Dye (Xcp), is an important disease of dry beans (Phaseolus vulgaris L.) worldwide (Saettler, 1989; Zaumeyer and Thomas, 1957). The pathogen is transmitted by seeds (Weller and Saettler, 1980; Zaumeyer, 1930). High temperature (25 to 30C), high relative humidity, frequent rains, and susceptibility are major

Plant regeneration has been achieved in two common bean lines from pedicel-derived callus that was separated from the explant and maintained through successive subcultures. Callus was induced either on B5 or MS medium containing 2% sucrose and enriched with 0.5 or 1.0 mg thidiaznron/liter alone or plus various concentrations of indoleacetic acid. The presence of 0.07 or 0.14 g ascorbic acid/liter in the maintenance media prolonged the maintenance time. Up to 40 shoot primordia were observed in 4-week-old cultures obtained from 40 to 50 mg callus tissues on shoot-induction medium containing 1-mg benzyladenine/liter. These shoot primordia developed two to five excisable shoots (>0.5 cm) on medium with 0.1-mg BA/liter. A histological study confirmed the organogenic nature of regeneration from the callus tissues. The R2 line from a selected variant plant showed stable expression of increased plant height and earlier maturity. Chemical names used: ascorbic acid, N- (phenylmethyl)-1H-pnrin-6-amine [benzyl-adenine, BA], 1H-indole-3-acetic acid (IAA), N- phenyl-N'-1,2,3-thiadiazol-5-ylurea [thidiazuron, TDZ].

Seedcoat color is an important trait, as it affects marketing and consumer acceptance of pinto beans (Phaseolus vulgaris L.). Pinto breeding line NE 94-4 showed seedcoat yellowing in on-farm field trials in Nebraska in 1996 and 1997. Hail, sprinkler irrigation, and fall rainfall appeared to be involved in increasing seedcoat yellowing, based on analysis of field and weather data of on-farm trial sites. The objective of this study was to determine the effect of moisture on seedcoat yellowing of pinto line NE 94-4 (susceptible) and pinto 'UI-114' (highly resistant). Two greenhouse experiments were conducted involving misting of bean plants near maturity and injecting water into maturing bean pods. Another experiment evaluated the response of seeds of these two bean entries to moisture by placing them on moist filter paper in petri dishes in the laboratory. Results showed that both genotype and moisture content are involved in seedcoat yellowing. This simple, cheap, and effective filter paper test was then used to evaluate seedcoat yellowing of nine pinto genotypes in response to moisture. Pinto NE 94-4 and 'Kodiak' showed the greatest change, while 'Bill Z' showed the least change, in seedcoat color. hilum. Smith (1961) proposed the genotype for the pinto seedcoat color, now correspond- ing to the genic nomenclature of Prakken (1972), as PCDJ (G) B (v) RK. G and v gene symbols in the above brackets were also re- cently assigned by M.J. Bassett, Florida State Univ., Gainesville (personal communication

Dry seeds from two lines of common bean (Phaseolus vulgaris L.) and one cultivar of faba bean (Vicia faba L.) were germinated on Murashige and Skoog (MS) medium containing B5 vitamins, 30 g sucrose/liter, and either 2.5, 5.0, or 7.5 µM benzyladenine (BA). Axenic seed cultures were grown at 22 to 24C in darkness and under continuous light from cool-white fluorescent tubes (40 µmol·m -2 ·s -1 ). Explant tissues were prepared from cotyledonary nodes (CN) and primary nodes (PN) of 14-day-old seedlings. Explants were cultured on corresponding seedling growth medium and maintained under continuous cool-white light (40 µmol·m -2 ·s -1 ). The percentages of CN and PN (in one line of common bean) explants that regenerated shoots and the number of shoots per explant (in all germplasm) were highest when nodal tissues were prepared from seedlings germinated in darkness. These responses were optimal on medium containing 5 µM BA during seedling growth and subsequent culture of explants. The number of shoots per explant was two to five times higher on explants cultured on medium with 0.25 to 1.0 µM forchlorfenuron (CPPU) or thidiazuron (TDZ) than on medium with 5 µM BA. Higher (2.5 and 5 µM) CPPU and TDZ concentrations inhibited shoot elongation and stimulated callus production. Histological analyses indicated that adventitious meristems formed 6 to 8 days after explant culture. Progenies from regenerated plants appeared similar to plants raised from the original seed stocks. Chemical names used: N- (phenylmethyl) -1 H- purin-6-amine (benzyladenine, BA); N- (2-chloro-4-pyridyl)- N'- phenylurea (forchlorfenuron, CPPU); N- phenyl -N' -1,2,3-thiadiazol-5-ylurea (thidiazuron, TDZ). Tissue culture of grain legumes using cotyledonary node ex- plants from in vitro-grown seedlings has been documented for organogenic competence (Jackson and Hobbs, 1990; McClean and Grafton, 19889; Wright et al., 1986). BA supplements (5 to 10 µM) in the medium during germination and subsequent explant culture were one of the most critical factors for organ- ogenic differentiation and shoot multiplication in this regener- ation system. N- (2-furanylmethyl)-1 H- purin-6-amine (kinetin) was ineffective (McClean and Grafton, 1989) for inducing mul- tiple-shoot organogenesis in common bean or in pea (Pisum sativum L.) (Jackson and Hobbs, 1990), and neither (E)-2-methyl- 4-(1H-purin-6-ylamino)-2-buten-1-ol (zeatin) nor N- (3-methyl- 2-butenyl)-1 H- purin-6-amine (2iP) could be substituted for BA in soybean (Glycine max (L.) Merr.) shoot regeneration studies

A new in vitro protocol was developed for multiple bud induction and plant regeneration from embryonic axis explants of four common bean (Phaseolus vulgaris L.) and two tepary bean (P. acutifolius A. Gray) lines. The explants were prepared from two embryo sizes, 3 to 4 mm and 5 to 7 mm, corresponding to pods collected after 15 and 25 days from flowering, respectively. The embryonic axis was cultured on Gamborg’s B5 basal medium with 0, 5, 10, or 20 μM BA in combinations with 0, 1, or 2 μM NAA. The cultures were maintained at 24 to 25C under continuous light or incubated in darkness for 2 weeks followed by continuous light before transfer to the secondary B5 medium (0 or 2 μM BA or 2 μM BA plus 4 μM GA3). Adventitious roots or a single shoot with roots formed on the explants cultured on media without plant growth regulators. Multiple buds were induced on all BA media, but more were produced with 5 or 10 μM for most lines. Dark incubation greatly enhanced multiple bud initiation. Shoot buds were not produced on media containing NAA alone or in combinations with BA. On the secondary medium, six to eight shoots per explant for common bean and up to 20 shoots per explant from tepary bean were observed after 3 weeks. Mature, fertile plants were produced from these shoots. Chemical names used: benzyladenine (BA); 1naphthaleneacetic acid (NAA); gibberellic acid (GA3). Efficient, repeatable, and rapid in vitro regeneration systems are a prerequisite for using recent advances in biotechnology to improve crop plants. Genetic transformation is one of the interesting areas of biotechnology for plant breeders because characteristics can be added with minimal alteration of the target plant’s genome. Therefore, direct shoot morphogenesis from the primary tissues is more desirable than going through an intermediate callus phase (Karp et al., 1982; Kovacs, 1985; Larkin and Scowcroft, 1981; Stiekema et al., 1988). A protocol for direct shoot organogenesis from cotyledonary node tissues was reported recently by McClean and Grafton (1989) in common bean (P. vulgaris). Also, shoot bud formation at the proximal notches from in vitro cultures of developing cotyledonary explants was described and its potential applications were discussed by Mohamed et al. (1991). However, plant regeneration from induced multiple buds and via direct shoot bud organogenesis from embryonic axis explants has not been reported in Phaseolus spp. If regenerative, the genotype of this explant could be produced in abundance from few seeds, and the explant meristematic tissues could be used directly for foreign gene insertion to produce transgenic plants (McCabe et al., 1988). Shoot bud organogenesis from embryonic explants also could be used to increase the efficiency of in vitro production of F1 hybrids in certain interspecific crosses that fail to germinate using the regular embryo rescue procedures (Chen et al.

Thirty four lines derived from a Pompadour landrace and three other lines from the Dominican Republic were co-inoculated with three cultures of Uromyces appendiculatus and three cultures of Xanthomonas campestris pv. phaseoli on separate leaves. The majority of the lines had dense trichomes (1–2 mm long) on the abaxial surfaces of upper leaves and developed small uredinia of moderate resistant rust reaction on the pubescent trifoliolate leaves and larger uredinia of moderate susceptible reaction on the primary glabrous leaves. Lines that lacked dense abaxial pubescence developed susceptible or moderate susceptible reactions on both primary and trifoliolate leaf stages. Differential reactions between strains of X. c phaseoli were observed on both leaf and pod infections and reactions on the leaf and on the pods were often different. Pompadour lines K, AE, R, and M had overall moderate resistance to three strains of X. c phaseoli and resistant or moderate resistance to three cultures of U. appendiculatus. These lines also have indeterminate growth habit associated with favorable and more stable seed yields and can now serve as valuable new germplasm sources for multiple disease resistance.

Although common blight disease is serious in many dry bean production areas, there is only limited information on the influence of photoperiod on the disease. Experiments were conducted in growth chambers and in the field (Nebraska, Dominican Republic, Puerto Rico) to investigate the influence of photoperiod × temperature and photoperiod, respectively, on the reaction of cultivars/lines to the causal bacterium Xanthomonas campestris pv. phaseoli. A split-plot design was used in all experiments except in the DR experiment where cultivars/lines were replicated within each photoperiod treatment. The disease reactions were more severe on cultivars/lines under short photoperiod and under higher temperature than under longer photoperiod and lower temperature in the growth chamber. Disease reactions were also more severe under the short photoperiod in the field experiments. No interactions were detected among these factors. These results have important implications for plant breeders in the evaluation of common blight disease reactions in different latitudes.

A simple protocol for leaf rooting in beans (Phaseolus vulgaris L.) was developed and used to investigate the reaction of Xanthomonas campestris pv. phaseoli (Xcp), causal pathogen of common bacterial blight disease, in detached versus attached bean leaves. Trifoliate leaves of different sizes (one-third, two-thirds, and fully expanded), either with or without the pulvinus attached to the petioles, were excised from 20 day-old plants of six bean cultivars/lines. Leaf cuttings were cultured in potting medium and then incubated for 5 to 10 days under transparent polyethylene plastic cover in the greenhouse. Roots were readily initiated along the petioles of the leaf cuttings, whether the pulvinus was present or absent. All leaves which were two-thirds expanded and fully expanded developed roots 5 to 7 days after culture. Eighty to 90 percent of the leaves which were one-third expanded formed roots 8 to 10 days after incubation. Laminae of the rooted leaf cuttings were viable and green during the 2 to 3 months period in culture after removing the plastic cover. The common bacterial blight reactions were similar for inoculated attached leaves, detached rooted leaves (inoculated either after or prior to rooting), and moistened detached leaves incubated without rooting. The latter were only usable for evaluation of the Xcp reaction in growth chamber experiments but not under greenhouse conditions. The rooted leaves would be useful for screening bean lines for multiple disease resistance, especially if the pathogens require different environments for disease expression.

Received for publication 14 June 1999. Accepted for publication 1 Aug. 1999. Published as Paper No. 12639, Journal Series, Nebraska Agricultural Research Division. The research was conducted under Projects 20-036 and 20-042. We acknowledge financial support for the development of this cultivar from the Nebraska Dry Bean Commission, Nebraska Dry Bean Growers Association, and the Title XII Bean/Cowpea (AID Contract No. DAN-1310G-SS-6008-00). We also appreciate technical advice and help from Dr. Anne Vidaver, Dr. Eric Kerr, Patricia Lambrecht, and Don Schaaf, Univ. of Nebraska Extension Center, Scottsbluff. This variety was named in recognition of Dr. John Weihing, former director of the Panhandle Research and Extension Center, Scottsbluff, Nebr. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. Dept. of Horticulture. To whom reprint requests should be addressed (e-mail: dcoyne1@unl.edu). Panhandle Research and Extension Center, Scottsbluff. West Central Research and Extension Center, North Platte. Dept. of Plant Pathology. Dept. of Food Science and Technology. Cooperative Extension Division, Gering. ‘Weihing’ Great Northern Diseaseresistant Dry Bean

Ten dry bean (Phaseolus vulgaris L.) cultivars/lines with differential reactions to rust were used in growth chamber experiments to determine rust [Uromyces appendiculatus (Pers.) Unger var. appendiculutus, (U a)], and common bacterial blight Xanthomonas campestris pv. phaseoli (E.F. Sm.) Dews. (X c p)] reactions on leaves when coinoculated with both pathogens. The X c p-U a necrosis symptoms were very different from those caused by X c p alone. Depending on the level of host susceptibility to rust, the X c p reaction remained confined within the rust pustule or spread beyond the pustule area, causing a necrosis of the entire leaf. Prior infection of bean seedlings with bean common mosaic virus (BCMV), NY-15 strain, reduced rust pustule size, but did not affect the reaction to X c p. Screening with X c p and BCMV can be done at the same time during the early vegetative stage, but the interactions of U a with X c p and of BCMV with U a need to be considered in screening for resistance.

YIELD STABILITY OF DETERMINATE AND INDETERMINATE RED MOTTLED BEANS

Common bacterial blight, incited by Xanthomonas campestris pv. phaseoli (Smith) Dye (Xcp), is a serious disease of common beans (Phaseolus vulgaris L.). Three experiments were conducted twice in growth chambers at 26 ± 1C under short (10 hours light/14 hours dark) and long (16 hours light/8 hours dark) photoperiods to determine the influence of these photoperiods, flower bud removal, pod development, and pre- and post-inoculation photoperiods on the reaction of common beans to Xcp. In one test, `PC-50' (susceptible; S) flowered earlier and was more susceptible to Xcp under the short photoperiod than under the long photoperiod. BAC-6 (resistant; R) flowered at the same time under both photoperiods but developed rapid leaf chlorosis (RLC) (hypersensitive reaction) under long photoperiods. Flowering and disease reactions to Xcp by XAN-159 (R) were similar under both photoperiods. In a second test, daily removal of flower buds of `PC-50' decreased its susceptibility to Xcp under the short photoperiod. RLC of inoculated leaves of BAC-6 occurred during flowering and pod development under both photoperiods. XAN-159 expressed a high level of resistance to Xcp but showed RLC at later pod development stages. In a third test, the disease reaction of `PC-50' was affected by the particular photoperiod applied post-inoculation but was not influenced by the photoperiod applied before inoculation with Xcp. The implications of these results in breeding beans for resistance to Xcp are discussed.

We studied leaf and pod reactions of 18 Phaseolus vulgaris germplasm lines (three temperate and 15 tropical) to four Xanthomonas campestris pv. phaseoli (XCP) (Smith) Dye strains and seven Uromyces appendiculatus (UA) (Pers.) Unger races. Line × XCP interaction was significant for leaf and pod reactions. The common bean lines XAN-159, BAC-6, and XAN-112 had the best combined leaf and pod resistance to XCP. Line × UA race interactions were significant (P = 0.05). Lines IAPAR-14 and BAC-6 had the best combined resistance to XCP and UA.

Iron deficiency chlorosis (FeDC) causes extensive reduction in yields of edible dry beans (Phaseolus vulgaris L.) grown on high-pH and calcareous soils. Fifteen bean cultivars/lines differing in response to FeDC were grown 2 years (1988 and 1989) on a high-pH (8.0), calcareous (2.3% calcium carbonate equivalent in surface 20 cm), and low-Fe (2.2 mg Fe/kg) Typic Haplustolls silt loam in the field (central Nebraska) to determine the effects of FeDC on seed yield of cultivars/lines sprayed with Fe. A significant interaction (P < 0.05) between cultivars/lines × Fe spray treatment was noted for visual FeDC ratings in 1988 only, and no significant interactions were noted for seed yield either year. Sprayed cultivars/lines generally produced higher yields than unsprayed ones. Overall increases were 47% in 1988 and 41% in 1989. Even though only slight FeDC was noted on some cultivars/lines receiving no Fe spray, seed yields were significantly increased when sprayed with Fe. Some cultivars/lines with moderate or moderately severe FeDC ratings did not show a significant increase in yield when sprayed with Fe, while other cultivars/lines did. Seed yield reductions for the cultivars/ lines per unit of FeDC rating (1 = green to 5 = severe chlorosis) were 915 kg·ha-1 for unsprayed and 1518 kg·ha-1 for sprayed plants in 1988 and 344 kg·ha-1 for unsprayed and 608 kg·ha-1 for sprayed plants in 1989.

Nine bean cultivars/lines (Phaseolus vulgaris L.) were grown in three soils/ rooting media at pH values of 7.9, 6.5, and 5.8 in greenhouse, growth chamber, and field experiments to evaluate the leaf reaction of the plants to a Nebraska bean rust (Uromyces appendiculatus (Pers.) Unger var. appendiculatus) isolate US85-NP-10-1. Significant differences were observed for rust pustule diameter between cultivars/lines grown in the three growth media. Plants grown in the medium at pH 5.8 showed significantly larger rust pustule diameters than those of plants grown at pH 6.5 or 7.9. A significant interaction occurred between growth medium and cultivars/lines for the rust reaction. Concentrations of Cl and Mn in leaves were positively correlated with rust pustule diameter. In contrast, concentration of K in leaves was negatively corre- lated with rust pustule diameter. Plant breeders attempting to improve beans for rust resistance must consider the growth medium pH in evaluating intensity and severity of rust symptoms on leaves. termine the relationship between the rust re- action of the plants and the nutrient concentrations of the leaf tissue. Eight cultivars/lines of dry beans with known differences in reaction to one Ne- braska isolate (US85-NP-10-1) of the bean rust pathogen were grown in three media in the greenhouse (Expt. I) and in the growth chamber (Expts. II and III). Medium 1 was Tripp sandy clay loam soil (coarse-silty, mixed, mesic Aridic Haplustolls) from the North Platte Research and Extension Center, Univ. of Nebraska, North Platte, with pH 7.9, 1.1% organic matter, 8.9 ppm P, 291 ppm K, 2.7 ppm NO 3, 0.5 ppm NH4, 10.4 cmol Ca, 3.5 cmol Mg, 0.9 cmol K, and 0.8 cmol Na/kg of soil. Medium 2 was Sharps- burg silty clay loam (fine, montmorillonitic, mesic Typic Arguidolls) from the Dept. of Horticulture experimental garden, Univ. of Nebraska, Lincoln, with pH 6.5, 2.9% or- ganic matter, 12.2 ppm P, 269 ppm K, 1.9 ppm NO 3, 0.6 ppm NH4, 15.8 cmol Ca, 5.5 cmol Mg, 0.9 cmol K, and 0.6 cmol Na/kg of soil. Medium 3 was a potting mixture consisting of equal volumes of sand, soil (Sharpsburg silty clay loam), vermiculite, and peat moss, with pH 5.8, 2.7% organic mat- ter, 5.8 ppm P, 157 ppm K, 0.5 ppm NO3, 0.5 ppm NH4, 5.3 cmol Ca, 2.8 cmol Mg, 0.4 cmol K, and 0.5 cmol Na/kg of soil. A randomized complete-block design with

Genetic variation for abaxial leaf pubescence was detected among dry bea n (Phaseolus vulgaris L.) cultivars/ lines. Inheritance of pubescence (long, straight hairs) was studied in the dry bean crosses of pubescent 'Pompadour Checa-50' (Dominican Republic) × eight glabrous cultivars/lines. Segregation for pubescence vs. glabrousness indicated that pubescence was determined by a single major gene or by duplicate recessive epistatic genes, depending on the cross involved. Trichome density (number trichomes per mm 2 ) was a quantitative trait. Thus, pubescence was a discrete trait, but trichome density ranged from low to high. Cultivars of dry beans commonly grown in the United States lack long, straight leaf hairs. However, some dry bean cultivars in the tropics possess long, straight leaf hairs at high density. Genetic variation for trichome type and density occurs in many plant species and has been shown to be associated with insect resistance (Levin, 1973; Ramalho and Ramos, 1979; Rogers, 1979; Webster, 1975). Shaik (1985) first reported negative cor- relations between leaf pubescence and low intensity of rust, pustules caused by Uromyces appendiculatus (Pers.) Unger var. appendiculatus (= U. phaseoli (Pers.) Wint.), in dry beans. Steadman and Shaik (1988) later reported a negative correlation of long, straight hairs on the abaxial leaves of adult plants with rust intensity. The protection offered by the long hairs is greatest when the leaves have not expanded. At such early stages, the leaf hairs are close enough to form a mat over the abaxial sur- faces, upon which droplets of water rest without making contact with the leaf epidermis. This phenomenon of water droplets condensing first on the leaf hairs and later forming a water layer was demonstrated by Burrage (1969). Thus, on hairy leaves, the rust germ tubes would be unable to make contact with the leaf epidermis (Alten, 1983). Rust is among the most destructive of the leaf diseases of dry bean (Kelly, 1982). The bean rust fungus is one of the most variable pathogens known (Vargas, 1980). Breeding of cultivars with race-specific resistance to all the known races of the path- ogen and to maintain stability of resistance is difficult. There is a need to explore alternative types of resistance, particularly those that would operate against all races of the fungus (Coyne and Schuster, 1975; Zaumeyer and Harter, 1941; Christ and Groth, 1982). We found no report on the inheritance of leaf pubescence in P. vulgaris, but quantitative inheritance was reported i n P. lun- atus L. (Lyman and Cardona, 1982). The objectives of this study were to investigate genotypic variation and the inheritance of the abaxial leaf pubescence trait in a wide array of dry bean crosses.