Summary
The inheritance of field resistance to downy mildew in lettuce derived from cv. Grand Rapids was studied in F2, F3 and F4 progeny from a cross with the more susceptible cv. Lobjoits Green Cos. The results for 32 randomly produced F3 families and the F2 population corresponded closely although the absolute level of resistance varied from season to season according to disease pressure and environmental conditions. The field resistance character showed a quantitative pattern of inheritance but the rapid response to selection at F3 implied that only a few genes may be involved. F4 families raised from families selected from the two extremes of the F3 distribution fell into distinct categories with resistance levels corresponding to that of their F3 parents. An association between resistance and morphological features of the resistant parent was present at F2 but not in subsequent generations when individuals and families which were as resistant as cv. Grand Rapids and yet bore little morphological resemblance to this cultivar were readily recovered.
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Norwood, J.M., Crute, I.R., Johnson, A.G. et al. A demonstration of the inheritance of field resistance to lettuce downy mildew (Bremia lactucae Regel.) in progeny derived from cv. Grand Rapids. Euphytica 32, 161–170 (1983). https://doi.org/10.1007/BF00036876
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DOI: https://doi.org/10.1007/BF00036876