Floral traits, ergot resistance and grain yield relationships in infected male-sterile sorghum A-lines.

摘要

Ergot (Claviceps africana) is a disease that affects non-fertilized ovaries in sorghum male-sterile plants and infects commercial hybrids grown under weather conditions that favours pollen sterility. In order to analyze the relationships among floral traits, stigma receptivity, and seed yield in plants inoculated with ergot, six pairs of A/B sorghum (Sorghum bicolor L. Moench) isogenic lines adapted to the Mexican Highlands (2200 m altitude) were sown under field conditions. The percentage of viable pollen was measured in B- lines, while days to flower, flowering period, stigma and panicle lengths, florets per panicle, floral density, rate of florets opening and flowering progress, were recorded in A-lines. In handmade A x B crosses, a 1x106 conidia mL-1 suspension was sprayed immediately after pollination, and 18 h later in vivo pollen grains adhered and germinated in the stigma, and fertilized pistils were counted. At harvest, number and percentage of diseased florets, seed yield, and yield components per panicle, were evaluated. The early flowering A-lines, with a shorter flowering period and a faster rate of florets opening showed less infected florets than the late flowering lines or than those with longer flowering period, but the healthiest lines were those that produced more florets per panicle, so both the total number of florets and the percentage of infected florets should be considered as complementary criteria for evaluating pathogen severity. The fungus caused decreases in stigma receptivity and seed yield. Averaged over crosses, the decrease in seed yield (40%) was larger than the disease severity (11%), thus pointing out the importance to link agronomic indexes to plant pathological criteria, when evaluating pathogen resistance.