Susceptibility to ergot in Zimbabwe of sorghums tbat 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 F| 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 daylengtb 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 sorghutns 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

Pathogenic Variation in Rhynchosporium secalis on Barley in Ethiopia

This paper presents the first detailed study on pathogenic variability in Rhynchosporium secalis in Ethiopia. Twenty four isolates of R. secalis, collected from Arsi, Bale and Shoa, major barley growing locations in Ethiopia, were tested on ten differential host cultivars, with known genes for resistance to the disease. The most frequent pathotypes were those inducing susceptible reactions on cvs Steudelli and Kitchen and the least complex pathotype identified was able to induce a susceptible reaction on these two cultivars only. Pathotypes 16 and 7 were the most complex and were able to induce susceptible reactions on 10 and 9 of the differential host cultivars respectively. These pathotypes were collected from research stations and were isolated from improved barley cultivars belonging to the malting barley type. The most frequent pathotype was pathotype 6 which was represented by four isolates from different locations in Arsi, Bale and Shoa. Pathogenic variation was detected amongst spores collected from the same field and from the same geographical location. The most effective resistance genes were those possessed by Turk, La-Mesita, Bey, Nigrinudum, Jet and Forrajera

Pathogenic Variation in Rhynchosporium secalis on Barley in Ethiopia

This paper presents the first detailed study on pathogenic variability in Rhynchosporium secalis in Ethiopia. Twenty four isolates of R. secalis, collected from Arsi, Bale and Shoa, major barley growing locations in Ethiopia, were tested on ten differential host cultivars, with known genes for resistance to the disease. The most frequent pathotypes were those inducing susceptible reactions on cvs Steudelli and Kitchen and the least complex pathotype identified was able to induce a susceptible reaction on these two cultivars only. Pathotypes 16 and 7 were the most complex and were able to induce susceptible reactions on 10 and 9 of the differential host cultivars respectively. These pathotypes were collected from research stations and were isolated from improved barley cultivars belonging to the malting barley type. The most frequent pathotype was pathotype 6 which was represented by four isolates from different locations in Arsi, Bale and Shoa. Pathogenic variation was detected amongst spores collected from the same field and from the same geographical location. The most effective resistance genes were those possessed by Turk, La-Mesita, Bey, Nigrinudum, Jet and Forrajera.