Abstract
Thirty sorghum lines were evaluated under humid tropical conditions in Mayagüez, Puerto Rico in 1980. In order of importance, bird damage, seed molds, and rust were the major constraints to optimum yields and seed quality. Finches (Fringillidae) mostly Tiaris bicolor and black birds (Icteridae) mostly Quiscalus niger were the most common sorghum eating birds. Seed losses from birds varied from 0 to 97.3% depending on the sorghum line. The mean loss from birds over all lines was 50.7%. Only two sorghum lines, IS 7013 der (0%) and SC0414-12 (ADN 252) (3%) suffered less than 10% seed losses. Over all sorghum lines a strong positive correlation (r = 0.81**) was found between severity of bird damage and the length of the period between 50% flowering and 50% physiological maturity. A low correlation (r = 0.39*) was found between the 125-seed weight and the severity of bird attack. Twentyfive genera of fungi were found on sorghum seeds. Clean seed frequency (seeds without signs of fungi) was highly correlated with seed germination in in vitro tests (r = 0.89**). During delayed harvest, visible mold on seeds increased markedly. Significant losses in seed germination were found at 1 and 2 weeks delayed harvest. Seeds infected with Fusarium moniliforme and Curvularia lunata were 60% lower in viability than noninfected seeds. Phoma spp. and Nigrospora sp. were associated with 20 to 40% reductions in seed viability. Colletotrichum graminicola did not lower seed viability of infected seeds. Sorghum rust severity varied from 0.6 to 46.6% among lines. All but 6 lines showed rust severity of less than 15%. Over all lines there was no significant correlation between rust severity and yield. Six rust susceptible lines (15 to 46.6% rust severity) yielded 63.8% ± 22.6 g/m2, whereas 6 of the most resistant lines (rust severity of less than 3%) yielded 126.6 ± 46.4 g/m2. Based on pest resistance, rapid grain fill and yield, IS 12610 der, IS 12661 der, and SCO(414-12) (ADN 252) appear to be excellent candidates for further testing at Mayagüez. In avoiding seed pests, sorghum lines appeared to benefit from a rapid germination and emergence, a comparatively long vegetative growth period, and a short uniform grain filling period.