Temperature and genotype interactions in the expression of host resistance in lettuce downy mildew
1992
Judelson, H.S. | Michelmore, R.W.
The influence of temperature and genotype on infection types determined by 13 gene-for-gene interactions between lettuce and the downy mildew fungus, Bremia lactucae, was evaluated. Lettuce seedlings containing each of 13 resistance (Dm) genes were inoculated with isolates of B. lactucae expressing various combinations of the matching avirulence genes, and incubated at 5, 10, 15, or 22 degrees C. Resistance, assessed by the absence of sporulation, became less effective at lower temperatures for Dm6, Dm7, Dm11, Dm15, and Dm16. No change was observed for resistance conditioned by eight other gene-for-gene interactions. Histological examination indicated that the extent of fungal development in host tissue was dependent on the interacting genotypes and on temperature. Manipulation of interactions involving Dm7 and Dm11, using temperature-shift incubation regimes, indicated that continued and cumulative exposure to permissive temperatures was required for effective resistance and suggested that the determinants of specificity are present in most host cells and are expressed throughout fungal development.
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