Ergot or sugary disease of sorghum has become an important constraint in North and South American countries that rely on F 1 hybrid seeds for high productivity. The objective of this research was to determine the vulnerability of various germplasm sources and publicly bred sorghum lines to sugary disease (Claviceps africana) in the United States. Flower characteristics associated with sugary disease resistance were also studied. A-/B-line pairs, R-lines, putative sources of resistance and their hybrid combinations with an A 3 cytoplasmic male-sterile source were evaluated using a disease incidence, severity, and dual-ranking system. Trials were planted in a randomized complete block design with three replications and repeated in at least two planting dates. Planting dates and pedigrees had significant effects on overall ranking for resistance. A-lines were most susceptible to sugary disease. R-lines were more susceptible than B-lines with respect to incidence and severity of the disease. Newer releases of A-and B-lines were more susceptible to sugary disease than older releases. Sugary disease reaction of A-lines was a good indicator of disease reaction of B-lines. Tx2737, a popular R-line, was highly susceptible to sugary disease in spite of being a good pollen shedder because the stigma emerged from glumes 2±3 days before anthesis. The combination of flower characteristics associated with resistance were least exposure time of stigma to inoculum before pollination, rapid stigma drying after pollination, and small stigma. An Ethiopian male-fertile germplasm accession, IS 8525, had good levels of resistance. Its A 3 male-sterile hybrid had the highest level of resistance in the male-sterile background. IS 8525 should be exploited in host-plant resistance strategies.
Preharvest desiccants are needed to reduce moisture content of grain sorghum [Sorghum bicolor (L.) Moench) for earlier harvest to preserve seed quality and quantity. Objectives of this study were (i) to examine the desiccant activity of glufosinate [2-amino-4-(hydroxymethylphosphinyl)butanoic acid] applied at several rates to grain sorghum at different seed moisture levels in contrasting environments and (ii) to determine the effect of glufosinate on germination and seedling growth of the treated crop. The soil at College Station (eastcentral Texas), was a Ships clay (very-fine, mixed, active, thermic, Chromic Hapludert); at Mayagiiez, PR, a Coto clay (very-fine, kaolinitic, isohyperthermic Typic Hapludox). Glufosinate was evaluated because of its contact herbicidal properties and limited systemic activity. In both Texas and Puerto Rico, glufosinate was applied at 0, 0.56, 1.1, or 2.2 kg ha-• to grain sorghum. Leaves and seed were sampled at 0, 1, 2, and 3 wk after treatment (W AT) for grain and leaf moisture. Seed was collected at 2 and 3 W AT for germination and growth studies. Glufosinate at all three treatment rates dried seed of the grain sorghum hybrid ATx638ffx2783 in Texas from >350 g kg-• grain moisture at application to a storable moisture of <120 g kg-• at 2 WAT, at which time untreated grain moisture was 150 g kg-•. Glufosinate rate did not affect grain moisture except at the high glufosinate rate at 1 W AT. Leaf moisture reduction was glufosinate rate-dependent, but all treatments significantly reduced leaf moisture content at 1 W AT. Germination and seedling growth were not affected by glufosinate treatment. Grain desiccation rate under a tropical en vi· ronment (Puerto Rico) was slightly slower than in Texas, but leaf moisture reduction was rapid and reached <300 g kg-• by 1 W AT from initial leaf moisture contents of 500 or 770 g kg-•. Germination was not adversely affected by glufosinate.
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