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A molecular marker associated with male fertility restoration was newly identified in onion in this study using random amplification of polymorphic DNA (RAPD) and bulk segregant analysis. A polymorphic amplicon from RAPD reaction was observed in DNA from fertile plants. The amplicon was designated as the RAPD marker OBC14.1000 and a 980-base pair (bp) nucleotide sequence was obtained. Genome walking was performed to obtain the flanking sequences of the OBC14.1000 marker to develop a co-dominant marker. The acquired sequences were a 2049-bp fragment linked to a male-fertile allele and a 1621-bp fragment linked to a male-sterile allele. Approximately 95% similarity was shown when the nucleotide sequences between fertile and sterile alleles were aligned. Using a polymorphic region containing a restriction site of Ava II in a fertile allele, the RAPD marker OBC14.1000 was successfully converted into a co-dominant CAPS marker and it was designated as ACms.1100. It appeared to be positioned much closer to the restorer-of-fertility locus, Ms , based on genotyping analysis as compared to other currently available markers. No putative homology was found to the newly identified ACms.1100 marker sequences through a Blast database search and the identification of sequences is still unknown.

Our objectives were to construct a randomly amplified polymorphic DNA (RAPD) marker-based linkage map using an F2 population derived from the melon (Cucumis melo) cross of ‘Deltex’ × TGR 1551, and map quantitative trait loci (QTL) for sucrose, total soluble solids (TSS), ratio of sucrose to total sugars (RSTS), and ascorbic acid as well as the ms-3 locus for male sterility previously reported in other muskmelon crosses. Due to the dominant character of RAPD markers, we scored 192 ‘Deltex’- and 158 TGR 1551-derived markers. One hundred eighty (94%) of the 192 markers fit the expected 3:1 ratio. On the basis of the 180 markers, we constructed a ‘Deltex’ linkage map of 171 markers distributed on 12 linkage groups (LGs) with a total map distance of 1182 cM. One hundred fifty (95%) of the 158 markers were identified to be nondistorted. We developed a TGR 1551 linkage map of 138 markers distributed on 12 LGs with a total distance of 1163 cM. A combined map of 12 LGs with a total map distance of 1394 cM was made from 82 marker pairs expressing codominance. Nine LGs were integrated into those of the existing composite map by 17 anchor markers. We mapped the ms-3 locus for male sterility on LG 9, which corresponds to LG 10 of the classical map and LG VII of the composite map. Six QTL for sucrose were located on LGs 2, 3, 4, 6, and 11. Three on LGs 3, 4, and 6 and four on LGs 2, 3, 6, and 11 of the six QTL for sucrose were also noted to be QTL for TSS and RSTS, respectively. A single QTL for ascorbic acid was placed on LG 5. This map will also be used to identify QTL for fruit sweetness, quality, size, and shape traits, as well as disease resistance.

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.

Our objectives were to identify RAPD and andromonoecious (a) markers associated with QTL for sucrose using bulked segregant analysis in an F 2 population from the melon (Cucumis melo L.) cross of 'TAM Dulce' (high sucrose) × TGR1551 (low sucrose) in a greenhouse experiment, and confirm the association of RAPD and a markers with sucrose QTL in an F 2 population from the different cross of 'Deltex' (high sucrose) × TGR1551 in a field experiment. Continuous distributions for sucrose were observed in the F2 populations indicating quantitative inheritance for the trait. A significant positive correlation was found between sucrose and total soluble solids (TSS). Nine RAPD markers were detected to be significantly associated with QTL for sucrose in the F2 population of the 'TAM Dulce' × TGR1551 cross in the greenhouse based on simple linear regression. Five unlinked markers associated with QTL were significant in a stepwise multiple regression analysis where the full model explained 39% of the total phenotypic variation for sucrose. Three to five of the nine RAPD markers were also observed to be significantly associated with QTL for glucose, fructose and TSS, respectively, suggesting that in this cross four sugar traits are controlled by the same QTL. Four RAPD markers were confirmed in the F 2 population of the 'Deltex' × TGR1551 cross in the field to be consistently associated with sucrose QTL. A significant association of a with sucrose was consistently expressed in our populations under greenhouse and field environments.

Our objectives were to identify randomly amplified polymorphic DNA (RAPD) markers associated with quantitative trait loci (QTL) for sucrose, total soluble solids (TSS), and sucrose percentage of total sugars (SPTS) using bulked segregant analysis in an F2 population from the melon (Cucumis melo L.) cross of `TAM Dulce' (high sugars) × TGR1551 (low sugars) in a greenhouse experiment, and confirm the associations of RAPD markers with QTL for these sugar traits in an F2 population from the different cross of `Deltex' (high sugars) × TGR1551 in a field experiment. Continuous distributions for sucrose, TSS, and SPTS were observed in the F2 populations indicating quantitative inheritance for the traits. Significant positive correlations were found between sucrose and TSS or SPTS. Nine RAPD markers were detected to be significantly associated with QTL for sucrose in the F2 population of the `TAM Dulce' × TGR1551 cross in the greenhouse based on simple linear regression. Five unlinked markers associated with QTL were significant in a stepwise multiple regression analysis where the full model explained 39% of the total phenotypic variation for sucrose. Five and seven of the nine RAPD markers associated with QTL for sucrose were also observed to be significantly associated with QTL for TSS and SPTS, respectively, suggesting that in this cross three sugar traits are controlled by the same QTL. Five RAPD markers were confirmed in the F2 population of the `Deltex' × TGR1551 cross in the field to be consistently associated with QTL for three sugar traits. Significant associations of andromonoecious (a) with both sucrose and TSS were consistently expressed in our populations under greenhouse and field environments. These RAPD and floral markers associated with the sugar synthesis QTL identified and confirmed here could be useful in melon breeding for improving the mature fruit sweetness.

Male sterility is an important trait of melon in F1 hybrid seed production. Molecular markers linked to a male-sterile gene would be useful in transferring male sterility into fertile melon cultivars and breeding lines. However, markers linked to the ms-3 gene for male sterility present in melon have not been reported. Our objectives were to identify randomly amplified polymorphic DNA (RAPD) markers linked to the ms-3 gene controlling male sterility using bulked segregant analysis in an F2 population from the melon cross of line ms-3 (male-sterile) × `TAM Dulce' (male-fertile), convert the most tightly linked RAPD marker to the ms-3 gene into a sequence characterized amplified region (SCAR) marker based on a specific forward and reverse 20-mer primer pair, and confirm the linkage of the RAPD and SCAR markers with the ms-3 gene in an F2 population from the cross of line ms-3 × `Mission' (male-fertile). A single recessive gene controlling male sterility was found in F2 individuals and confirmed in F3 families. Two RAPD markers that displayed an amplified DNA fragment in the male-sterile bulk were detected to be linked to the ms-3 gene in the F2 population from the cross of line ms-3 × `TAM Dulce'. RAPD marker OAM08.650 was closely linked to the ms-3 gene at 2.1 cM. SCAR marker SOAM08.644 was developed on the basis of the specific primer pair designed from the sequence of the RAPD marker OAM08.650. The linked RAPD and SCAR markers were confirmed in the F2 population from the cross of line ms-3 × `Mission' to be consistently linked to the ms-3 gene at 5.2 cM. These markers were also present in 22 heterozygous fertile F1 plants having the ms-3 gene. The RAPD and SCAR markers linked to the ms-3 gene identified, and confirmed here could be utilized for backcrossing of male sterility into elite melon cultivars and lines for use as parents for F1 hybrid seed production.

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.

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.

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.

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.

Mature fruit size and shape are important traits of most melon types. Our objective was to identify RAPD markers associated with major QTL affecting fruit weight, length, diameter and shape by means of bulked segregant analysis in an F2 population from the ananas melon cross of Deltex (larger fruit size) × TGR1551 (smaller fruit size). Clear separations for fruit weight, length, diameter, and shape between Deltex and TGR1551 were observed. Continuous distributions for fruit weight, length, diameter and shape were found in the F2 population indicating quantitative inheritance for the fruit traits. Significant positive correlations were detected between fruit weight and shape traits (r = 0.73 to 0.80). A significant positive correlation was observed between fruit weight and glucose (r = 0.35) or fructose (r = 0.25), whereas no correlation was noted between fruit weight and sucrose or total soluble solids. Two small and large bulks for fruit weight and shape were developed from F2 plants. A total of 240 primers were used to simultaneously screen between the small and large bulks, and between Deltex and TGR1551. Twenty-six RAPD markers were polymorphic for the small and large bulks. Ten markers were found to be significantly and consistently associated with fruit size and shape traits on the basis of simple linear regression. Of the 10 markers associated, four displayed an amplified DNA fragment in the small bulk, while six showed an amplified DNA fragment in the large bulk. The associated marker OJ07.350 explained 15% to 27% of the phenotypic variation for the fruit traits. These markers associated with QTL for melon fruit size and shape are expected to be useful in melon breeding programs for modifying fruit size.

Muskmelons (Cucumis melo L.) play an important role in the American diet. Ranked as one of the top 10 most-consumed fruits by the USDA, cantaloupe melons have the highest amount of beta-carotene of all the ranked fruits. Beta-carotene, also called pro-Vitamin A, is an essential nutrient required for eye health, and may have the potential, as an antioxidant to reduce the risks associated with cancer, heart disease, and other illnesses. Breeding melons with increased levels of beta-carotene will benefit consumer health. Research has found phytonutrients are most bioavailable when consumed in their fresh form, rather than as vitamin supplements. The high level of beta-carotene found in some melons has a genotypic component, which may be exploited to breed melons high in beta-carotene. Molecular markers and marker-assisted selection (MAS) can be used to increase the efficacy of the breeding process, while lowering breeding costs. An F2 population was created using `Sunrise', the female parent, containing no beta-carotene crossed with `TAM Uvalde', a high beta-carotene variety. A field population consisting of 115 F2 individuals and a greenhouse population containing 90 F2 individuals were grown. The resulting fruit were screened phenotypically and ranked according to beta-carotene content. Chisquare values fit the previously reported model of a single dominant gene for presence of beta-carotene (orange-flesh) vs. absence (green or white flesh). A continuous distribution of beta-carotene concentrations from high to low suggested quantitative inheritance for this trait. Two eight-plant DNA bulks composed of either high or low beta-carotene F2 individuals were screened for polymorphic molecular markers using the amplified fragment-length polymorphism technique.

The ratio of individual sugar compositions is an important fruit quality trait in muskmelon. Our objective was to identify RAPD markers associated with QTL for percentage of each individual sugar (sucrose, glucose, and fructose) using bulked segregant analysis in an F2 population derived from the melon cross of `TAM Dulce' (high sucrose percentage of total sugars) x TGR1551 (low sucrose percentage of total sugars). Continuous distributions for sucrose, glucose, and fructose percentages of total sugars were observed in the genetic population indicating quantitative inheritance for the traits. A significant positive correlation was observed between sucrose percentage and sucrose (r= 0.89) or soluble solids (r= 0.33), whereas a significant negative correlation was noted between sucrose percentage and glucose percentage (r = –0.85) or fructose percentage (r = –0.58). A total of 500 primers was used to screen between low and high DNA bulks for three individual sugar percentages. Ten RAPD markers, four amplified from `TAM Dulce' and six amplified from TGR1551, were significantly associated with QTL for at least one individual sugar percentage. Of the 10 markers identified, six were consistently associated with two to three traits. The OAU13.1350 obtained from `TAM Dulce' accounted for 13% and 19% of the phenotypic variation for sucrose and glucose percentages, while OAW06.600 obtained from TGR1551 explained 17% and 18% of the variation for the two traits. The OAA09.350 and OAU05.600 markers accounted for 4% to 13% of the variation for three sugar percentages. These markers associated with QTL for three individual sugar compositions could be useful in melon breeding for improving the mature fruit quality.

Sucrose, fructose, total sugars and soluble solids are major factors in determining mature melon fruit sweetness. Bulked segregant analysis was utilized to detect RAPD markers associated with QTL for sucrose, total sugars and soluble solids in an F2 population from the ananas melon cross of Deltex (high sugars) × TGR1551 (low sugars). Sucrose, glucose, fructose and total sugar data were obtained from 108 F2 plants by means of HPLC. Clear separations for sucrose, total sugars and soluble solids between Deltex and TGR1551 were observed, whereas slight differences for glucose and fructose were found. Continuous distributions for sucrose, total sugars and soluble solids were observed in the F2 population indicating quantitative inheritance for the sweetness traits. A significant negative correlation was observed between sucrose and glucose (r = -25) or fructose (r = -0.31). A significant positive correlation was noted between sucrose and total sugars (r = 0.80) or soluble solids (r = 0.64). Three low and high DNA bulk pairs for sucrose, total sugars and soluble solids were developed. A total of 360 primers were used to simultaneously screen between the low and high bulks, and between Deltex and TGR1551. Sixty-eight RAPD markers were polymorphic for the low and high bulks. Of the 68 markers, 24 were found to be significantly associated with sucrose, total sugars or soluble solids on the basis of single-factor ANOVA. Marker OM15.550 was consistently associated with QTL affecting sucrose, glucose, fructose, total sugars and soluble solids, and accounted for 7% to 25% of the phenotypic variation for the traits. These markers associated with the sugar synthesis QTL could be useful to transfer these genes into a low sugar cultivar to enhance the fruit sweetness.

This study was carried out to optimize conditions for plant regeneration of sweetpotato [Ipomoea batatas (L.) Lam] using shoot tips, petioles, and leaves of Selection 75-96-1 as explants in Murashige and Skoog (MS) with several growth regulators at different levels. Callus initiation and callus proliferation media were 9.0 μm 2,4-dichlorophenoxyacetic acid (2,4-D) and 9.0 μm 2,4-D + 1.1 μm N6-benzyladenine (6-BA) in protocol I; 8.1 μm α-naphthaleneacetic acid (NAA) + 1.2 μm kinetin (KIN) and 5.4 μm NAA + 4.6 μm KIN in protocol II; 0.9 μm 2,4-D, and 0.9 μm 2,4-D + 1.2 μm N-isopenylamino purine (2iP) in protocol III; NAA (8.1 μm) + KIN (1.2 μm) and 2,4-D (0.9 μm) + 2ip (1.2 μm) in protocol IV, respectively. In protocol I and II, shoot tip, petiole, and leaf were used, but only petiole and leaf in protocol III and IV. In the protocol I and II, somatic embryos were obtained only from shoot tip explants; in protocol III and IV, only from petioles. The frequencies of somatic embryo development were 33.3% in protocol I, 42.1% in protocol II, 21.2% in protocol III, and 10.3% in protocol IV, respectively. The leaf explants failed to produce somatic embryos in all the experiments. In protocol I, somatic embryogenesis occurred through the well-known sequence of globular-, heart-shaped-, torpedo-, and cotyledon-type embryos. However, in protocol II, the structures resembling plumule and radicle were observed before the emergence of torpedo/cotyledon type embryo clusters. The somatic embryogenesis in protocol III and IV was similar to that in protocol I. Growth regulators influenced somatic embryo development. Further, this study showed that explant resource and growth regulators affected the frequency of plant regeneration in sweetpotato.

The objective was to detect molecular markers associated with QTL for partial physiological resistance (PPR) to two white mold (WM) isolates, partial field resistance (PFR), plant architecture (PA), and plant height (PH) in a genetic linkage map constructed using recombinant inbred lines (RILs) from the cross `PC-50' (resistant to WM) × XAN-159 (susceptible to WM). Significant correlations (+0.39 and +0.47) were noted between the WM reactions in the greenhouse and field. A significant but negative correlation (–0.33) was observed between the WM reaction and PH in the field. Six QTL affecting PPR to isolate 152 were found on LGs 4, 5, 7, and 8. Six QTL affecting PPR to isolate 279 were found on LGs 2, 3, 4, 7, and 8. Five QTL for PFR were observed on LGs 2, 5, 7, 8, and 11. Two QTL affecting PA were detected on LGs 7 and 8. Two QTL affecting PH were identified on LGs 7 and 8. On one end of LG 8 marker H19.1250 was significant for PPR to both isolates. On the other end of LG 8 the region closely linked to the C locus was significantly associated with PPR to both isolates, PFR, PA and PH. Marker J09.950 on LG 7 was significantly associated with PPR to both isolates, PFR, PH and seed weight. Marker J01.2000 on LG 2 was the most significant locus for both PPR to the isolate 279 and PFR. QTL on LG 5 were found for PPR to the isolate 152 and PFR. Overall, four of the five QTL affecting PFR were also found for PPR to one or both isolates.

Bean rust, caused by Uromyces appendiculatus, is an important disease of common bean (Phaseolus vulgaris L.). The objective was to identify RAPD markers linked to the gene (Ur-6) for specific resistance to rust race 51 using bulked segregant analysis in an F2 segregating population from the common bean cross pinto `Olathe' (resistant to rust) × great northern Nebraska #1 selection 27 (susceptible to rust). A single dominant gene controlling specific resistance to race 51 was hypothesized based on F2 segregation, and then was confirmed in the F3 generation. A good fit to a 3:1 ratio for band presence to band absence for each of three markers was observed in 100 F2 plants. Three RAPD markers were detected in a coupling phase linkage with the Ur-6 gene. Coupling-phase RAPD marker OAB14.600 was the most closely linked to the Ur-6 gene at a distance of 3.5 cM among these markers. No RAPD markers were identified in a repulsion phase linkage with the Ur-6 gene. The RAPD markers linked to the gene for specific rust resistance of Middle American origin detected 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.

Several experiments were conducted to evaluate the influence of explant type, sucrose level, and callus development time on sweetpotato [Ipomoea batatas (L.) Lam] in vitro culture. Shoot tip, petiole, and leaf of Selection 75-96-1 was used as explants in Murashige and Skoog (MS) media with different plant growth regulators. Calli derived from shoot tip and petiole produced 42.1% and 10.3% somatic embryos, respectively, but the leaf failed to produce somatic embryos. The effect of sucrose level was determined using shoot tip as explants. Compared with 3% sucrose in the same plant growth regulators level medium during callus initiation and callus proliferation periods, 5% sucrose level suppressed root growth and improved shoot regeneration. The callus development time was measured by using shoot tips on callus initiation medium containing 1.5 mg/L alpha-Naphthaleneacetic acid (NAA) and 0.25 mg/L Kinetin (KIN) plus 5% sucrose. When explants were cultured for less than 6 weeks during callus initiation, then transferred onto plant regeneration medium, plant regeneration via organogenesis occurred; whereas, maintaining cultures for more than 12 weeks on the same callus initiation/proliferation medium, plant regeneration was favored via embryogenesis. Explant type and other factors affecting plant regeneration noted here could be applied to protoplast culture, somatic hybridization, and transformation in sweetpotato.

Bean rust, caused by Uromyces appendiculatus, is a major disease of common bean (Phaseolus vulgaris). The objective was to identify RAPD markers linked to the gene (Ur-7) for specific resistance to rust race 59 using bulked segregant analysis in an F2 segregating population from the common bean cross GN1140 (resistant to rust) × Nebraska #1 (susceptible to rust). A single dominant gene controlling specific resistance to race 59 was found in the F2 and was confirmed in the F3. Seven RAPD markers were detected in a coupling-phase linkage with the Ur-7 gene. Coupling-phase RAPD markers OAA11.500, OAD12.550, and OAF17.900 with no recombination to the Ur-7 gene were found. Three RAPD markers were identified in a repulsion-phase linkage with the Ur-7 gene among the three markers at a distance of 8.2 cM. This is the first report on RAPD markers linked to the Ur-7 gene in common bean. The RAPD markers linked to the gene for specific rust resistance of Middle American origin detected here, along with other independent rust resistance genes from other germplasm, could be used to pyramid multiple genes into a bean cultivar for more-durable rust resistance.

Common bacterial blight, incited by Xanthomonas campestris pv. phaseoli (Xcp), is a serious disease of common bean (Phaseolus vulgaris). RAPD markers and flower color (V gene) previously had been reported to be associated with six 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. Our 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 RI backcross population from the cross BC2F6 `PC-50' × XAN-159 and for leaf resistance to Xcp in a F2 population from a different cross Pinto `Chase' × XAN-159 could be confirmed. Among six QTL previously detected, five in the RI backcross population and three in the F2 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 F2 population. The confirmed marker BC437.1050 and V gene on linkage group 5, along with other resistance genes from other germplasm, could be used to pyramid the different genes into a bean cultivar to enhance the resistance to Xcp.

Common bacterial blight (CBB) in common bean (Phaseolus vulgaris L.), caused by Xanthomonas campestris pv. phaseoli (Xcp), reduces bean yields and quality throughout the world. Pinto `Chase' is a high-yielding variety with moderate resistance to Xcp derived from great northern Nebraska #1 selection 27, whose resistance is derived from an unknown tepary (P. acutifolius) bean source. XAN-159 is a black mottled small seeded breeding line with different genes for high resistance to Xcp derived from a different tepary source (PI 319443). Our objective was to pyramid different genes for Xcp resistance from the donor parent XAN-159 into the rust-resistant recurrent parent Pinto `Chase' using the classical back-cross breeding method with confirmation of resistance using RAPD molecular markers. Resistance was confirmed in some BC2F2 generation plants. Seven RAPD markers and the V locus (flower color) previously identified were confirmed in the BC1 and BC2 populations. Smaller seed size, purple flower color, and black mottled seed coat color were coinherited with resistance to Xcp. However, a recombinant plant with enhanced CBB resistance and moderate-sized pinto seed was identified. Backcross breeding is being continued.

Seed size is an important trait in common bean. The objective was to identify RAPD markers associated with QTL for seed weight, seed length, and seed height in a molecular marker-based linkage map in a recombinant inbred (RI) population from the common bean cross of the larger seeded (100 seed/39 to 47 g) PC-50 (ovate seed shape) × smaller seeded (100 seed/26 to 35 g) XAN-159 (flat rhomboidal seed shape). The parents and RI lines were grown in two separate greenhouse and two field (Wisconsin, Dominican Republic) experiments using a RCBD. Continuous distributions for seed weight, seed length, and seed height were observed for RI lines indicating quantitative inheritance. One to three QTLs affecting seed weight explained 17% to 41% of the phenotypic variation. Two to three QTLs for seed length explained 23% to 45% of the phenotypic variation. One to four QTL associated with seed height explained 17% to 39% of the phenotypic variation. A RAPD marker M5.850 in linkage group 3 was consistently associated with seed weight, seed length, and seed height in all experiments and explained 7% to 13% of the phenotypic variation for these traits. A seedcoat pattern morphological marker (C) in linkage group 1 was associated with seed weight and seed height in two greenhouse experiments.

Common bacterial blight (CBB), incited by Xanthomonas campestris pv. phaseoli (Xcp), is an important disease of common bean (Phaseolus vulgaris L.). Tepary bean (P. acutifolius A. Gray) is of interest to bean breeders because of resistance to CBB. The objective was to identify RAPD markers linked to major dominant genes for CBB resistance and purple flower color using bulked segregant analysis in an F2 population from a tepary bean cross Nebr#19 [resistant (R) to CBB and white flower color] × Nebr#4B [susceptible (S) to CBB and purple flower color]. Ten RAPD primers (600 RAPD primers screened) showed polymorphisms between bulked DNA derived from R and S plants. All markers showed coupling linkage with CBB resistance. The RAPD marker of G-14 primer was 5.2 cM distant from the gene for resistance to Xcp strain LB-2. The RAPD marker of L-18 primer was 6.8 cM distant from the gene for resistance to Xcp strain SC-4A. The RAPD marker of G-14 primer was 26.2 cM distant from the gene for resistance to Xcp strain EK-11. Seven RAPD primers showed polymorphisms between bulked DNA derived from purple and white flower plants. All markers showed coupling linkage with the gene for purple flower color. The RAPD marker of Y-6 primer was 3.6 cM distant from the gene for purple flower color.

Plant growth habit is an important trait. Our objective was to identify RAPD markers linked to major gene for indeterminate growth habit using bulked segregant analysis in an F2 population from a bean cross Chichara (indeterminate growth habit × PC-50 (determinate growth habit). A total of 132 RAPD primers (600 RAPD primer screened) showed polymorphisms between bulked DNA derived from indeterminate and determinate plants. All markers showed coupling linkage with indeterminate growth habit. RAPD markers of A-8, A-17, C-7, C-15, D-4, D-5, F-6, F-16, G-9, H-3, H-20, and I-7 were 2.2 cM distant from the gene for indeterminate growth habit. Markers of B-7, B-16, B-17, C-8, E-1, F-1, F-20 and H-l9 primers were 4.6 cM distant from the gene for indeterminate growth habit.

Common bacterial blight (CBB), incited by Xanthomonas campestris pv. phaseoli (Xcp), an important disease in common bean (Phaseolus vulgaris L.) Tepary bean (P. acutifolius A. Gray) is of interest to bean breeders because of resistance to CBB. Our objective was to identify RAPD markers linked to major genes for CBB resistance using bulked segregant analysis in an F2 population from a tepary bean cross CIAT640005 (R) X Nebr#4B (S). A total of 57 RAPD primers (602 RAPD primers screened) showed polymorphisms between bulked DNA derived from R and S CBB plants. All markers showed coupling linkage with CBB resistance. A good fit to a 3:1 ratio of bands for presence and absence using 11 RAPD primers was observed in 77 F2 plants. Markers of U-15 and L-7 primers were 2.4 cM distant from the gene for resistance to Xcp strain LB-2. RAPD markers of U-10, U-20, S-12, Y-4, F-13, P-6, Q-1, and Q-ll primers were 2.4 cM distant from the gene for resistance to Xcp strain SC-4A. RAPD markers of IJ-15 and L-7 primers were 8.4 cM distant from the gene for resistance to Xcp strain EKl l. The tepary RAPD linkage group includes three molecular markers and three genes for resistance to Xcp strains EK-l l, LB-2, and SC-4A and spans a length of 19.2 cM. This data supports the presence of Xcp races.