Field and Greenhouse Evaluations of Stem Canker Resistance in Soybean

Abstract

Greenhouse screening using infested toothpicks was compared to field evaluation of soybean [Glycine max (L.) Merr.) breeding lines for resistance to stem canker disease, caused by southern strains ofDiaporthe phaseolorum (Cke. & E11. (Sacc.) var. caulivora Athow and Caldwell (Dpc). Field screenings are reliable indicators of resistance, but often the disease does not develop naturally in field screening nurseries. Thirty‐seven random F4:6 lines from the cross ‘Hutton’ (susceptible ) ✕ ‘Tracy M’ (resistant) were evaluated for their reaction to Dpc in the field (two locations, 2 yr) under natural infestation and infection conditions, and in the greenhouse (three experiments) with artificial inoculation using infested toothpicks. Our objectives were to compare field and greehouse screening and to determine the usefulness of greenhouse inoculation in predicting the yield and disease reaction of breeding lines when these lines were subjected to natural field infection conditions. Field screening based on symptoms and yield was highly effective in identifying resistant genotypes. Heritabilities for yield and disease ratings in the field were 87 and 92%, respectively. The toothpick inoculation procedure used in the greenhouse was effective with each of three Dpc isolates (different in geographic origin from the field location) in identifying the genotypes that showed highest levels of disease resistance in the field. Phenotypic correlations between greenhouse ratings and yield in the infested field ranged from −0.71 to −0.61. Results indicated that selection based on greenhouse screening can be an effective alternative to field screening when resistance is derived from Tracy M.

Reaction of soybean lines to stem canker

“…To discriminate genotypes with different levels of susceptibility posterior evaluations are necessary, as for example the evaluation 40 DAI. This observation is in line with the results presented by Weaver et al (1988).…”

“…assumed that cultivars with field resistance carry distinct alleles from those present in the other cultivars (Backman et al 1985, Weaver et al 1988.…”

“…Evaluations were realized 10, 20, 40, and 73 days after inoculation (DAI). Based on the last evaluation and according to the criterion proposed by Weaver et al (1988), the reaction of the genotypes was classified as: R = resistant (score = 1.0); MR = moderately resistant (score between 1.1 and 2.0); MS = moderately susceptible (score between 2.1 and 3.0); S = susceptible (score between 3.1 and 4.0); or HS = highly susceptible (score > 4.1).…”

“…In this sense, the toothpick method is recommended in the EUA for the evaluation of genotypes whose resistance source is Tracy M, while for genotypes whose resistance is derived from Centennial, the reaction should be evaluated under field conditions (Backman et RL Backes et al al. 1985, Weaver et al 1988. Our study had the following objectives: investigation of the reaction of some F 8 lines to stem canker, observation of the consistence of the visual scores throughout the evaluation periods and evaluation of the concordance between scores based on different number of plants per row.…”

Development of SCAR marker linked to stem canker resistance gene in soybean

“…The period of 30 days after inoculation was considered as a limit for the final evaluation of the plants, in agreement with Kilen et al (1985), Kilen and Hartwig (1987), Weaver et al (1988), Bowers Jr. et al (1993. In the χ 2 test the results indicated the presence of one gene with dominant action in the parentals Tracy-M and BR92-15454, governing plant resistance to stem canker (Table 1).…”