GENOTYPE AND PLANTING DATE EFFECTS ON THE QUALITY OF SORGHUM SEEDS INFECTED WITH ERGOT

Abstract

Ergot (Claviceps africana Frederickson, Mantle & de Milliano) is a disease that decreases sorghum (Sorghum bicolor L. Moench) seed yield. Moreover, seeds near infected flowers become contaminated with honeydew and exudates thus enhancing saprophytic fungus colonization and decreasing seed quality. Germination, viability, vigor, electrical conductivity, weight and sanitary quality of seed from two male-sterile sorghum lines were evaluated. Lines were sown in two planting dates (May and June 2006,) in Montecillo, State of México (2200 m altitude). Treated and non-treated seeds with fungicide (Thiram®), in combination with three levels of C. africana severity (0, 10 y 50 %) on panicles naturally infected under field conditions, were also compared. Eight days after harvest, genotype and sowing date showed higher effects (P ≤ 0.05) than fungicide application and C. africana severity, on the physical and physiological seed quality traits. Seed quality, germination and vigor of the line A1 were superior to the corresponding values of line A9. Seed from plots sown in May 5th had higher quality than those sown in June 10th. On the average, fungicide treated seed had 31 % less fungus colonies than non-treated seed, while seeds from healthy panicles had half of the colonies than those showing 50 % of ergot severity. In general, sanitary quality was affected by the ergot damage in the field but not by the fungicide treatment.