Evaluation of sorghum germplasm used in US breeding programmes for sources of sugary disease resistance

摘要

Ergot or sugary disease of sorghum has become an important constraint in North and South American countries that\udrely on F1 hybrid seeds for high productivity. The objective of this research was to determine the vulnerability of\udvarious germplasm sources and publicly bred sorghum lines to sugary disease (Claviceps africana) in the United\udStates. Flower characteristics associated with sugary disease resistance were also studied. A-/B-line pairs, R-lines,\udputative sources of resistance and their hybrid combinations with an A3 cytoplasmic male-sterile source were\udevaluated using a disease incidence, severity, and dual-ranking system. Trials were planted in a randomized complete\udblock design with three replications and repeated in at least two planting dates. Planting dates and pedigrees had\udsignificant effects on overall ranking for resistance. A-lines were most susceptible to sugary disease. R-lines were\udmore susceptible than B-lines with respect to incidence and severity of the disease. Newer releases of A- and B-lines\udwere more susceptible to sugary disease than older releases. Sugary disease reaction of A-lines was a good indicator of\uddisease reaction of B-lines. Tx2737, a popular R-line, was highly susceptible to sugary disease in spite of being a good\udpollen shedder because the stigma emerged from glumes 2±3 days before anthesis. The combination of flower\udcharacteristics associated with resistance were least exposure time of stigma to inoculum before pollination, rapid\udstigma drying after pollination, and small stigma. An Ethiopian male-fertile germplasm accession, IS 8525, had good\udlevels of resistance. Its A3 male-sterile hybrid had the highest level of resistance in the male-sterile background. IS\ud8525 should be exploited in host-plant resistance strategies.