White Mold In Common Bean Research Articles

Control of apothecia of Sclerotinia sclerotiorum by soil amendment with S–H mixture or Perlka ® in bean, canola and wheat fields

Ascospores of Sclerotinia sclerotiorum produced from apothecia are the primary source of inoculum for causing diseases such as white mold of common bean, pod rot of pea, stem blight of canola and head rot of sunflower and safflower in the Canadian prairies. A field study was conducted for 4 years to determine efficacy of control of production of apothecia from carpogenically germinated sclerotia of S. sclerotiorum by soil amendment with Perlka ® (calcium cyanamide) and S–H mixture (a formulated compound). Results of the 4-year experiments showed that amendment of soil with Perlka ® at low (30 g/m 2) or high (60 g/m 2) rate was effective in reducing carpogenic germination of sclerotia and production of apothecia under the canopy of host crops (common bean and canola) and a non-host crop (wheat). In the experiments of 1988, for example, the numbers of apothecia produced in the treatments of Perlka ®-low rate (30 g/m 2), Perlka ®-high rate (60 g/m 2) and untreated control were 42, 46, and 182 apothecia/plot (m 2), respectively, for bean; 89, 42, and 318 apothecia/plot (m 2), respectively, for canola; and 146, 143, and 412 apothecia/plot (m 2), respectively, for wheat. However, soil amendment of S–H mixture at low (30 g/m 2) or high (60 g/m 2) rate was ineffective in reducing carpogenic germination of sclerotia and production of apothecia for all the 4 years of testing in all three crops. The ineffectiveness of S–H mixture and the practicality of Perlka ® for control of Sclerotinia diseases of crops grown under Canadian prairie conditions are discussed.

Identification of QTL Associated with White Mold Resistance in Common Bean

White mold, caused by the necrotrophic fungusSclerotinia sclerotiorum(Lib.) de Bary, is a serious disease of common bean (Phaseolus vulgarisL.). The use of resistant cultivars is the preferred control strategy, but the approach has been difficult to implement because of quantitative nature of genetic resistance to white mold. The objectives of this study were to identify quantitative trait loci (QTL) associated with resistance toS. sclerotiorum, identify QTL associated with agronomic traits that contribute to white mold avoidance, and locate putative QTL on the integrated bean map. Bulked segregant analysis using multiple trait bulks that included disease severity index (DSI), yield, and days to flower was used to detect QTL associated with field resistance to white mold in a Middle American recombinant inbred line (RIL) population of common bean. QTL that accounted for 9.2 to 14.7% of the phenotypic variation for DSI were located on linkage groups B2, B5, B7, and B8 of the integrated bean map. In addition, QTL were detected for seed size and yield and agronomic traits associated with disease avoidance: days to maturity, days to flower, and lodging. Heritability estimates for DSI were moderate (0.41) and correlations with agronomic traits that included lodging (0.56**), architecture (0.35**), canopy height (−0.33**), and yield (−0.64**) support the importance of these traits in disease avoidance. Data from the current study provides breeders with critical information on which traits and genomic regions to target as part of an overall strategy to enhance resistance to white mold in common bean.

QTL Conferring Resistance and Avoidance to White Mold in Common Bean

White mold, caused by Sclerotinia sclerotiorum (Lib.) De Bary, is a serious fungal disease that negatively affects production of common bean (Phaseolus vulgaris L.). Resistance to white mold in common bean is complexly inherited and comprised of physiological resistance and avoidance mechanisms. The objectives of this research were to discover quantitative trait loci (QTL) conferring resistance to white mold in navy beans, to determine if a multitrait bulking strategy was an efficient approach for locating QTL conferring resistance to white mold, and to identify agronomic traits associated with QTL for white mold avoidance in the field. A 98 F 3 -derived Bunsi/Newport population was evaluated in three environments for resistance to white mold and agronomic traits. A 28 recombinant inbred line population derived from a Huron/Newport cross was evaluated for the resistance and yield in four environments and was used to confirm marker associations. Marker BC20.1800 on B2 was associated with disease severity index (DSI) (12%) across environments, and was confirmed in the second population. Markers linked to QTL were also detected on B7 for DSI (17%), resistance to oxalate (16%), yield (37%), as well as days to flowering (14%), branching pattern (9%), lodging (9%) and seed size (20%). Growth habit unexpectedly mapped to B7, and represents a novel source of determinacy in navy bean. Multiple-trait bulking based on low DSI, high yield, and 40 to 45 d to flowering versus high DSI, low yield, and 40 to 45 d to flowering effectively identified more markers linked to QTL for resistance to white mold than did bulks based on low and high DSI alone. Selection based on QTL that confer resistance to white mold, such as the Bunsi-derived QTL located on B2 and B7 of the bean genome, combined with certain desirable agronomic traits offers the opportunity to develop resistant cultivars and improve our understanding of resistance to white mold in common bean.

QTL Conferring Resistance and Avoidance to White Mold in Common Bean

QTL Conferring Resistance and Avoidance to White Mold in Common Bean

Agronomic Traits Affecting Resistance to White Mold in Common Bean

Resistance to white mold [caused by Sclerotinia sclerotiorum (Lib.) de Bary] in common bean (Phaseolus vulgaris L.) is complexly inherited, and highly influenced by environmental factors. The identification of agronomically desirable avoidance mechanisms in advanced or elite lines and segregating populations is essential. The objectives of this study were to determine the relationship between nine agronomic traits (growth habit, days to flower, canopy height and width, branching pattern, lodging, days to maturity, seed size, and yield) and resistance to white mold in the field, corresponding heritabilities of resistance and agronomic traits, and the effect of the agronomic traits on disease and seed yield. A group of elite lines, and two recombinant populations derived from crosses between two resistant navy bean cultivars, Bunsi and Huron, to a susceptible cultivar, Newport, were evaluated for disease severity index (DSI) and agronomic traits in multiple field seasons. Heritability estimates for DSI were moderate (0.47) in the Bunsi/Newport population and high (0.82) in the Huron/Newport population. All agronomic traits displayed moderate to high heritability estimates. The agronomic traits that associated significantly with DSI in the three populations differed greatly. The most important agronomic trait that reduced DSI and contributed to yield was indeterminate growth habit. Increased canopy height, width, and lodging were generally associated with an increase in DSI, whereas traits such as days to flower and maturity varied in relation to DSI and yield across environments and populations. The complexity of the relationship of agronomic traits to DSI and yield highlights the difficulties bean breeders face in selecting among elite lines and within segregating populations for resistance to white mold in the field.

Agronomic Traits Affecting Resistance to White Mold in Common Bean

Resistance to white mold [caused by Sclerotinia sclerotiorum (Lib.) de Bary] in common bean (Phaseolus vulgaris L.) is complexly inherited, and highly influenced by environmental factors. The identification of agronomically desirable avoidance mechanisms in advanced or elite lines and segregating populations is essential. The objectives of this study were to determine the relationship between nine agronomic traits (growth habit, days to flower, canopy height and width, branching pattern, lodging, days to maturity, seed size, and yield) and resistance to white mold in the field, corresponding heritabilities of resistance and agronomic traits, and the effect of the agronomic traits on disease and seed yield. A group of elite lines, and two recombinant populations derived from crosses between two resistant navy bean cultivars, Bunsi and Huron, to a susceptible cultivar, Newport, were evaluated for disease severity index (DSI) and agronomic traits in multiple field seasons. Heritability estimates for DSI were moderate (0.47) in the Bunsi/Newport population and high (0.82) in the Huron/Newport population. All agronomic traits displayed moderate to high heritability estimates. The agronomic traits that associated significantly with DSI in the three populations differed greatly. The most important agronomic trait that reduced DSI and contributed to yield was indeterminate growth habit. Increased canopy height, width, and lodging were generally associated with an increase in DSI, whereas traits such as days to flower and maturity varied in relation to DSI and yield across environments and populations. The complexity of the relationship of agronomic traits to DSI and yield highlights the difficulties bean breeders face in selecting among elite lines and within segregating populations for resistance to white mold in the field.

An indirect test using oxalate to determine physiological resistance to white mold in common bean

In common bean (Phaseolus vulgaris L.), the detection of physiological resistance to white mold [Sclerotinia sclerotiorum (Lib.) de Bary] in the field is confounded by environmental factors and plant avoidance mechanisms. Development of a reliable screening procedure is needed to identify resistant bean germplasm and to develop resistant cultivars. The objective of this study was to determine if oxalate, a primary pathogenicity factor of S. sclerotiorum, could be used to indirectly screen for physiological resistance to white mold in common bean. Cut bean seedlings were placed in a 20 mM oxalate solution in the greenhouse. Genotypes were rated based on differences in wilting response to oxalate. Oxalate ratings of the 27 genotypes were correlated with field ratings of a white mold disease severity index and incidence , and negatively correlated with yield . The oxalate test is an efficient method to indirectly test for physiological resistance to white mold in common bean.

Using a Subsample of the Core Collection to Identify New Sources of Resistance to White Mold in Common Bean

Few sources of physiological resistance to the fungal pathogen Sclerotinia sclerotiorum (Lib.) de Bary, causal organism of white mold disease in common bean (Phaseolus vulgris L.), have been found and exploited by breeders. Our objective was to screen a subsample of the core collection of P. vulgris accessions representing the active USDA National Plant Germplasm System collection of 1698 accessions from Central and South America for reaction to white mold using a greenhouse straw test. White mold reactions were rated for 89 accessions from 1 = no disease symptoms to 9 = total plant collapse. Eleven core accessions, Pis (plant introductions) 152311, 207136, 207154, 290990, 290995, 293353,313850, 415886, 415906, 415913, and 415936, with scores <5 were identified as having putative physiological resistance to white mold. An expanded screening among 35 accessions from the active collection which had similar passport data to the resistant core Pis 207136, 290990, and 313850 revealed 20 resistant accessions with disease scores <5. A similar expanded screening of 18 accessions with similar passport data to core Pis 310674, 313608, and 415954 that had scores >6, revealed only four accessions with scores <5. These results indicated that a subsample of the core collection was useful for identifying ranges of accessions within the active Phaseolus collection that possessed a high incidence of putative physiological resistance to white mold.