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Differences were found in the expression of resistance of perennial ryegrass, Lolium perenne, cultivars to crown rust, Puccinia coronata Corda, when plants were incubated at either 10 degrees C or 25 degrees C. In an extreme example, all the genotypes of 'Carrick' were resistant at 10 degrees C but susceptible at 25 degrees C. The variation between cultivars was due both to a general increase in expression of susceptibility and the proportion of plants which became susceptible. A BC1 line containing a stay-green gene derived from Festuca pratensis was insensitive to temperature, while a sister line was sensitive.Peer reviewe

Improving breeding strategies for adaptation to water-deficit stress is an important challenge to increasing coffee yields.In a nine-year experiment, 18 genotypes were tested under drought-stress and non-stress conditions to select adaptable genotypes to drought stress. Efficiency of indirect selection based on agronomic traits related to drought-stress was also assessed relative to direct selection based on yield. Drought stress significantly limited fruit-set and yields by 51-75% in all 18 genotypes. Clustering the genotypes based on seven-year average yields under stress and non-stress conditions and their drought susceptibility index ( DSI) resulted in the direct selection of eight generally adaptable genotypes. These were characterized by low DSI and high yields in drought-stress and non-stress environments. These genotypes should serve as materials for breeding for drought tolerance or for direct utilization as planting material under drought-stress and non-stress conditions. The first three-year average yield was 75% as efficient as the seven-year average yield; the last four-to seven-year yields gave similar results. Indirect selection by clustering of the genotypes according to span (crown diameter) and fruit set was 75% as efficient as direct selection based on seven-year average yields. The efficiency of the first three-year yield as well as span and fruit set in selecting adaptable genotypes, coupled with the determination of these traits at the early stages of the growing cycle, further demonstrates that genotypes adaptable to water-deficit stress can be selected in the early stages of the breeding program.

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