Susceptibility to ergot in Zimbabwe of sorghums that remained uninfected in their native climates in Ethiopia and Rwanda

Forty‐four local Ethiopian and Rwandan sorghums (Sorghum bicolor) were observed to remain free of ergot, or had only low incidence, in their natural equatorial latitudes and were potentially of interest, in the design of male‐sterile lines for F1 hybrid breeding, if they possessed a physiologically based resistance mechanism. These sorghums were therefore also investigated under natural and artificial disease pressures in Zimbabwe where unadapted development and inappropriate long daylength prevented flowering in 18 accessions. Of the remaining 16 Ethiopian and 10 Rwandan accessions which flowered, only one from each country remained free of ergot. The susceptibility expressed was ascribed to observed asynchrony of stigma exsertion with anthesis. In the Rwandan accession that persistently remained free of ergot in Zimbabwe, histology of ovules showed pollination before floret gaping, so that a general principle of disease escape due to efficient pollination is proposed for the Ethiopian and Rwandan sorghums in their native climates. The findings emphasize that cleistogamy is a desirable character for avoiding ergot infection in self‐fertile sorghums and suggest that the Ethiopian and Rwandan sorghums may not generally be useful for breeding ergot‐resistant male‐sterile female lines. However, a few accessions deserve more detailed study as a potential genetic resource, before a firm conclusion that all apparent resistance is disease escape owing to efficient pollination.