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Japanese Erwinia pyrifoliae strains cause bacterial shoot blight of pear (BSBP) in Japan. The genetics of Japanese Erwinia remains largely unknown relative to the abundant genomic information available for other Erwinia strains. We compared the genome of Japanese and Korean E. pyrifoliae strains along with those of E. amylovora and E. tasmaniensis. Comparisons with the Korean E. pyrifoliae strain revealed numerous gene insertions/deletions, rearrangements, and inversions in the central regions of the chromosomes. Approximately 80% (2843) of coding DNA sequences (CDSs) are shared by these two genomes which represent about three-quarters of the genome, and there are about 20% unique CDSs. Comparative analysis with closely related erwinias showed that 1942 (more than 50%) core open reading frames (ORF) are shared by all these strains. In addition to two type III secretion systems (hrp/dsp and inv/spa), the genome of Ejp617 encodes numerous virulence factors, including a type VI secretion system, an exopolysaccharide synthesis cluster, and another protein secretion system present in plant pathogenic Erwinia strains. The availability of whole genome sequence should provide a resource to further improve the understanding of pathogenesis in Japanese E. pyrifoliae Ejp617 and to facilitate evolutionary studies among the species of the genus Erwinia. Key words: bacterial shoot blight, Japanese Erwinia pyrifoliae, whole genome, pathogenicity genes. Les souches japonaises de l'Erwinia pyrifoliae causent le feu bacterien au Japon. La genetique des Erwinia japonais demeure largement inconnue en comparaison avec l'information genomique abondante au sujet d'autres souches de l'Erwinia. Les auteurs ont compare les genomes de souches japonaises et coreennes de l'E. pyrifoliae avec ceux de l'E. amylovora et de l'E. tasmaniensis. Les comparaisons avec les souches coreennes de l'E. pyrifoliae ont revele de nombreux rearrangements, insertions/ deletions et inversions au sein des regions centrales des chromosomes. Environ 80 % (2843) des regions codantes etaient communes aux deux genomes ce qui represente environ trois quarts du genome, et il y avait environ 20 % de sequences codantes uniques. Des analyses comparees avec des Erwinia apparentes ont montre que 1942 (plus de 50 %) des cadres de lecture communs etaient partages par toutes ces souches. En plus de deux systemes de secretion de type II (hrp/dsp et inv/spa), le genome de la souche Ejp617 code pour de nombreux facteurs de virulence, incluant un systeme de secretion de type VI, un amas de genes pour la synthese d'exopolysaccharides et un autre systeme de secretion proteique present chez des souches phytopathogenes de l'Erwinia. La disponibilite de la sequence du genome entier procure une ressource de plus pour approfondir la connaissance de la pathogenese chez la souche japonaise Ejp617 de l'E. pyrifoliae ainsi que pour faciliter les etudes evolutives parmi les especes du genre Erwinia. [Traduit par la Redaction] Mots-cles: feu bacterien, Erwinia pyrifoliae japonais, genome complet, genes de pathogenicite., Introduction Japanese Erwinia strains causing bacterial shoot blight of pear (BSBP) were first isolated from Nashi pears in Hokkaido, Japan (Beer et al. 1996). The disease symptoms were almost indistinguishable [...]

Stemphylium blight (caused by Stemphylium botryosum Wallr.) is one of the major diseases of lentil (Lens culinaris Medik.) in South Asia and North America. The objective of the study was to identify linkage map position of the genes conferring resistance to stemphylium blight and the markers linked to the genes for its utilization in marker-assisted breeding. A population of 206 [F.sub.7]-derived recombinant inbred lines (RILs) was developed from a cross between ILL-6002 (resistant) and ILL-5888 (susceptible). The RILs were planted in disease-screening plots at Ishurdi, Bangladesh in the 2006-2007 and 2008-2009 winter cropping seasons. Significant variation was detected among RILs for disease scores and frequency distributions suggested complex inheritance. An intraspecific linkage map was constructed that comprised 139 markers; 21 simple sequence repeats (SSR), 27 randomly amplified polymorphic DNA (RAPD), 89 sequence related amplified polymorphism (SRAP) markers and 2 morphological markers distributed over 14 linkage groups. One significant quantitative trait loci (QTL) was detected based on disease scores from the 2006-2007 experiment while three significant QTLs were detected from the 2008-2009 experiment. The QTL [QLG4.sub.80-81] was common in both years and accounted for 25.2 and 46.0% of the variation of disease scores in 2006-2007 and 2008-2009 experiments, respectively. Two SRAP markers, ME5XR10 and ME4XR16c, and one RAPD marker, UBC34, located on linkage group 4, were significantly associated with the [QLG4.sub.80-81] in both crop years. After validation, the more tightly linked ME4XR16c marker may be used for marker assisted selection for stemphylium blight resistance. doi: 10.2135/cropsci2009.12.0709

Stripe rust is a devastating fungal disease that afflicts wheat in many regions of the world. New races of Puccinia striiformis, the pathogen responsible for this disease, have overcome most of the known race-specific resistance genes. We report the map-based cloning of the gene Yr36 (WKS1), which confers resistance to a broad spectrum of stripe rust races at relatively high temperatures (25[degrees] to 35[degrees]C). This gene includes a kinase and a putative START lipid-binding domain. Five independent mutations and transgenic complementation confirmed that both domains are necessary to confer resistance. Yr36 is present in wild wheat but is absent in modern pasta and bread wheat varieties, and therefore it can now be used to improve resistance to stripe rust in a broad set of varieties.

Susceptibility to black spot [caused by Mycosphaerella pinodes (Berk. and Blox.) Vestergr.] and weak stem strength in field pea (Pisum sativum L.) are major restrictions to yield, seed quality, and ease of harvest. Previous studies have established that additive genetic variance is present for both traits, and that stem strength is strongly associated with a field test of compressed stem thickness at the base of the stem. This study aimed to improve these two complex traits simultaneously by recurrent selection. Heritabilities and responses to selection for resistance to black spot and stem strength were evaluated during two cycles of recurrent selection after intercrossing diverse genotypes. Response to selection was indicated by a reduction of 10% in the mean black spot leaf disease in the [F.sub.2] of cycle 2 compared with the [F.sub.2] of cycle 1, when considered as a percentage of the mean of cycle 1 parents in the same trials. Likewise, there was a 15% increase in stem strength, based on the mean compressed stem thickness in the [F.sub.2] of cycle 2 compared with the [F.sub.2] of cycle 1. Broad sense heritability for resistance to black spot leaf disease was moderate (H = 0.63 [+ or -] 0.35 across cycles 1 and 2) and for compressed stem thickness was also moderate (H = 0.66 [+ or -] 0.34). Genetic gains were realized for both traits simultaneously in the first two cycles and were predicted to be rapid over the next five to six cycles based on a random mating quantitative genetics model.

Abstract: Scab, caused by the fungal pathogen Venturia inaequalis, is the most common disease of cultivated apple (Malus xdomestica). The fungal races 6 and 7 have now overcome the major [...]

Karnal bunt (Tilleria indica Mitra) infestation of wheat (Triticum aestivum L.) kernels reduces grain quality. Deployment of genetic resistance would be preferable to chemical applications for control of the disease. Inoculation studies were carried out in a wheat mapping population with the aim of locating genes for resistance. Recombinant inbred (RI) lines from a cross between a resistant synthetic wheat (Triticum turgidum `Altar 84' x T. tauschii) and the susceptible common wheat cultivar `Opata 85' were inoculated with Karnal bunt sporidial suspension and evaluated for symptom development in the field for three seasons and in the greenhouse. Based on restriction fragment length polymorphism (RFLP) analyses, regions on chromosome arms 3BS and 5AL carrying marker alleles from the Altar durum parent were consistently associated with reduced kernel disease. Main marker effects accounted for up to 32% of disease variation in the field but only 15% in the greenhouse, where the level of disease was higher, suggesting an environmental component of resistance. The tagging of these Karnal bunt partial-resistance genes in tetraploid and hexaploid backgrounds may facilitate the accumulation of resistance via marker-assisted transfer to susceptible durum and common wheat cultivars. This practice should reduce laborious disease screening requirements., Karnal or partial bunt (KB) was first identified in 1931 in wheat fields near Karnal, India. Susceptible wheat cultivars are attacked via floral infection by seed-, air-, or soil-borne sporidia, [...]

Common bean (Phaseolus vulgaris L.) production in the humid tropics would benefit from the selection of cultivars with greater levels of resistance to web blight, a devastating disease caused by Rhizoctonia solani Kuhn. This will require screening techniques that are sensitive enough to detect moderate levels of resistance. Greenhouse experiments evaluated the effectiveness of a droplet inoculation technique for screening five [F.sub.5:6] segregating populations for resistance to web blight. Another objective was to estimate the heritability of resistance to web blight in five common bean populations. Significant differences in lesion size were detected among [F.sub.6] lines within each population. Lines with less web blight infection than the resistant parent MUS83 were observed in each population. This suggests that both parents contributed to the resistance of the progeny. Narrow sense heritability estimates for web blight reaction ranged from 0.61 to 0.79. These relatively high heritabilities suggest that selection for smaller lesion size may be effective in earlier generations when MUS83 is used as a source of resistance to web blight. Physiological resistance to web blight, as measured by lesion size by means of the droplet inoculation technique, will need to be combined with disease avoidance traits such as erect architecture to obtain effective resistance in the field. Five lines from the MUS83 x DOR483 population with smaller lesion sizes in the greenhouse had moderate to low levels of web blight infection in field experiments conducted in Puerto Rico and the Dominican Republic., Web blight is caused by Rhizoctonia solani Kuhn, which is the asexual stage of the basidiomycete fungus Thanatephorus cucumeris (Frank) Donk. In the humid lowland tropics of Latin America and [...]

A model by Levin and Udovic (1977) emphasizes the need for integration of studies of the numerical abundances and genetic composition of host and pathogen species. We use their conceptual framework to summarize our collaborative research on the ecological genetics of the anther-smut disease of Silene alba caused by the fungus Ustilago violacea. Our theoretical investigations have revealed the importance of the rate and mode of disease transmission on the likelihood of coexistence between host and pathogen. Our empirical studies have quantified patterns of disease spread on local and regional spatial scales and have shown that host genotypes differ greatly in resistance. Comparable genetic variation in pathogen virulence has not yet been demonstrated. The genetic composition of host populations alters numerical dynamics in experimental populations: disease declines in resistant populations, while host and pathogen appear to coexist in susceptible populations. Ecological outcomes also may be affected by the negative relationship between disease incidence and host flowering time, which may constitute a 'cost' to resistance. We are currently expanding our work on the ecology and genetics of metapopulation dynamics of host and pathogen. Key words: anther-smut; coexistence; disease ecology; host; pathogen; population ecology; population genetics; Silene alba; transmission; Ustilago violacea., INTRODUCTION The need for an integration of population ecology and population genetics has been repeatedly recognized (Levin and Udovic 1977, Lewontin 1979, Antonovics and Via 1988). Studies of disease demonstrate [...]

A dispersed, moderately repetitive sequence in Cryphonectria parasistica, thecausal agent of chestnut blight, was cloned in pMS5 and used for DNA fingerprinting studies. DNA fingerprint analysis showed that pMS5 detected two linked fragments. Hybridization patterns did not change during vegetative growth or during sporulation. The results showed that the C. parasitica population is partly clonal in structure, with 6 of the 33 fingerprint genotypes occurring twice. However, a large portion of the individuals in the population result from sexual reproduction.

The hypovirulence phenotype in Cryphonectria parasitica, the causalagent of chestnut blight, is associated with a cytoplasmic, double-stranded RNA(dsRNA) virus. Factors which may restrict the transfer of this dsRNA were studied. The findings indicate that dsRNA can be transferred among compatible and incompatible isolates of C. parasitica. However, this transfer is limited due to the antagonistic interactions among the incompatible isolates. Furthermore, transfer occurs only through substrate hyphae. Temperature is alsoan important factor limiting transfer. Freezing temperatures cause a loss of the dsRNA.

Obtaining kernel discoloration (KD) resistance in malting barley (Hordeum vulgare L.) is an important breeding objective in the midwestern USA. This study was undertaken to evaluate a cyclic breeding procedure for transferring quantitative KD resistance across a wide genetic gap, and to obtain parental germplasm or a new cultivar having KD resistance combined with good agronomic performance and malting quality. Six cycles of crossing and selection were done beginning in 1970 to incorporate KD resistance genes from |Chevron' and CI 9539 into Minnesota barley lines. Chevron and CI 9539 were inferior for both agronomic and quality traits. Subsequently, 45 sixth-cycle derived lines were evaluated in inoculated disease nurseries and in field trials to determine whether resistance was transferred and to assess agronomic and malting quality merit. Kernel discoloration resistance was successfully transferred using the cyclic breeding procedure, although the resistance level tended to be below that of the resistance sources. The derived lines were similar to the local cultivars Robust and Morex for agronomic and quality traits, except for kernel plumpness, and to a lesser degree malt extract. They showed marked overall improvement compared with the resistance sources, Chevron and CI 9534, and a few of the lines merit consideration as potential cultivars. Unconscious selection was hypothesized to account for the intermediate level of KD resistance observed in local germplasm. In this situation, cyclic recurrent breeding appeared to be a good choice for incorporating a quantitative disease trait into a good genetic background., A cyclic breeding procedure was used to incorporate kernel discoloration (KD) resistance to high-agronomic value cultivars of malting barley. Six cycles of breeding were performed using KD resistant cultivars Chevron and CI 9539 as the original sources of resistance. The most resistant lines in each cycle were crossed to the best performing germplasm at the time. Results showed that KD resistance was transferred, while maintaining most of the desireable agronomic and malting quality traits.

We describe in this study punchless, a nonpathogenic mutant from the rice blast fungus M. grisea, obtained by plasmid-mediated insertional mutagenesis. As do most fungal plant pathogens, M. grisea differentiates an infection structure specialized for host penetration called the appressorium. We show that punchless differentiates appressoria that fail to breach either the leaf epidermis or artificial membranes such as cellophane. Cytological analysis of punchless appressoria shows that they have a cellular structure, turgor, and glycogen content similar to those of wild type before penetration, but that they are unable to differentiate penetration pegs. The inactivated gene, PLS1, encodes a putative integral membrane protein of 225 aa (Pls1p). A functional Pls1p-green fluorescent protein fusion protein was detected only in appressoria and was localized in plasma membranes and vacuoles. Pls1p is structurally related to the tetraspanin family. In animals, these proteins are components of membrane signaling complexes controlling cell differentiation, motility, and adhesion. We conclude that PLS1 controls an appressorial function essential for the penetration of the fungus into host leaves.

Disease is a major problem in creeping bentgrass (Agrostis stolonifera L.) on golf course putting greens. Genetic composition and uniformity of host populations can affect disease development. This study was conducted to determine the effects of blending creeping bentgrass cultivars on dollar spot (caused by Sclerotinia homoeocarpa F. T. Bennett) severity. `Penn A-4', `Crenshaw', `L-93', `Mariner', and `Penncross' were planted in monostands or as two-way or three-way blends in a completely random design with three replications on a sand-based putting green in the field at College Station, TX. Disease severity was determined by the number of infection centers and by total blighted area. Crenshaw was most susceptible, L-93 most resistant, and all other cultivars were moderately resistant to dollar spot in monostands. Cultivar susceptibility in monostands to S. homoeocarpa was representative of each cultivars contribution to dollar spot severity in blends. In blends, L-93 suppressed, whereas Crenshaw increased dollar spot. Penncross, Penn A-4, and Mariner did not affect dollar spot severity across all blend combinations. Number of infection centers and infected area pooled across all monostands were similar when compared to all two- and three-way blends indicating that dollar spot activity in blends was a compromise between resistance levels of individual cultivars. Two-way blends of Penn A-4, L-93, Mariner, or Penncross with Crenshaw, however, resulted in 46 to 67% fewer infection centers and 71 to 98% less blighted area, when compared to the Crenshaw monostand. These data indicated that blending a resistant cultivar with a susceptible cultivar reduced dollar spot severity in the blended population., CREEPING BENTGRASS is a widely utilized turfgrass species on golf course putting greens across the USA and around the world. Disease is a major problem in creeping bentgrass and one [...]

Physiological resistance is an important component of integrated strategies used to control white mold [caused by Sclerotinia sclerotiorum (Lib.) de Bary], a major disease of common bean (Phaseolus vulgaris L.) in North America. Information pertaining to inheritance of physiological resistance, as detected by the greenhouse straw test, and its relationship with field resistance is lacking. The objectives of this study were to compare physiological resistance as detected by two separate straw tests with field resistance, evaluate heritability of physiological resistance, and to characterize the disease reaction of G 122 by quantitative trait locus (QTL) analysis. This was done in a recombinant inbred population (A 55/G 122) consisting of 67 [F.sub.8]-derived lines. The greenhouse tests with five and six replications, respectively, and the field test with three replications were conducted in randomized complete block designs. Moderate heritability for disease reaction (scored from 1 = no symptoms to 9 = severe disease) was observed across the straw tests (0.65) and in the field (0.78). Inheritance of disease reaction was further investigated with a framework linkage map composed of 74 markers. Interval mapping detected a QTL on linkage group B7 near the phaseolin seed protein (Phs) locus that explained 38% of the phenotypic variation for disease score across the straw tests. The same B7 QTL (26%), and an additional QTL (18%) on B1 near the fin gene for determinate growth habit, conditioned field resistance. A QTL (34%) for canopy porosity, a measure of potential disease avoidance, also mapped to the fin locus. Results confirmed that physiological resistance as detected by the straw test was an integral component of field resistance, and that both physiological and avoidance mechanisms contributed to field resistance in the A 55/G 122 population. The landrace G 122 clearly provides breeders with a heritable source of physiological resistance to combat white mold disease., WHITE MOLD is one of the most important fungal diseases of common bean worldwide. Combining physiological resistance with avoidance mechanisms (upright plant architecture, open canopy) is the current breeding strategy [...]

Septoria tritici blotch (STB), a fungal foliar disease of wheat (Triticum aestivum L.) caused by Septoria tritici Rob. ex Desm., is a major constraint to wheat production worldwide. Understanding the inheritance of resistance in known resistant genotypes would potentially lead to more efficient deployment of host plant resistance. In our study, inheritance of seedling STB resistance was evaluated by an eight-parent full diallel set of crosses. Parents, [F.sub.1], and reciprocal [F.sub.1] were planted in a greenhouse on three different dates. Within each planting date, three to five seeds of each entry were planted in a randomized complete block design with three replicates. Plants at the second-leaf stage were inoculated with a bulk of six S. tritici isolates. Significant general combining ability (GCA), specific combining ability (SCA), and reciprocal effects were observed in the analysis of variance. The ratio of GCA sum of squares relative to SCA sum of squares suggested that GCA was more important than SCA. Additive gene effects played a major role in host response to STB, while nonadditive gene effects were also detected. General combining ability effects of individual genotypes were in a close agreement with parental performance. `KS94U338', a genotype with putative resistance derived from Aegilops tauschii Coss., had the lowest STB score and the highest general combining ability. Our results suggested that KS94U338, which possesses resistance thought to be distinct from other known sources, should prove useful in breeding efforts to improve STB resistance in wheat., SEPTORIA TRITICI BLOTCH of wheat (syn. Septoria leaf blotch or speckled leaf blotch), caused by S. tritici [teliomorph Mycosphaerella graminicola (Fuckel) J. Schrot.], causes significant losses in wheat production worldwide [...]

HYBRIDIZATION IS LEADING TO RAPID EVOLUTION OF DUTCH ELM DISEASE AND OTHER FUNGAL PLANT PATHOGENS Plant disease epidemics resulting from introduction of exotic fungal pathogens are a well-known phenomenon. Limited [...]

Summers in the southeastern USA produce a harsh environment for survival of white clover (Trifolium repens L.) stolons. Long periods of drought and hot temperatures are interspersed with rain showers that create ideal conditions for fungal pathogenesis. Previous studies indicated that Macrophomina phaseolina (Tassi) Goidanich may be an important pathogen that limits survival of white clover stolons in the summer. The objective of this study was to determine the range in response of 20 white clover cultivars, germplasms, and breeding and naturalized populations for resistance to M. phaseolina using a leaf tissue assay. Discs were cut from leaves excised from 50 plants of each entry and inoculated with an agar plug cut from the margin of a M. phaseolina colony. Leaf discs were scored according to the rate of necrosis induced by the pathogen. The experiment was conducted as a randomized complete block with four replicates and was repeated with 50 additional plants from each entry. Differences in responses of entries to inoculation with M. phaseolina were observed in each run of the experiment. Brown Loam Syn. 2 germplasm and North GA population had the least disease and the greatest number of plants selected as resistant to M. phaseolina. Large-leaf plants selected for resistance gave highly consistent responses when retested, with 35% of the plants having no leaf necrosis following inoculation with M. phaseolina. The leaf tissue assay was not as reliable for selecting consistent resistant phenotypes among small-leaf white clover entries, as 37% of the plants selected as resistant were rated as susceptible upon retesting. Resistance to M. phaseolina was observed in adapted white clover germplasm, and development of new cultivars with this resistance should improve white clover summer survival., STOLONS are the means by which individual white clover genotypes persist in the field. The seedling taproot system only survives for the first year or two of growth. When the [...]