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Inheritance of Downy Mildew Resistance in Alfalfa 1
Author(s) -
Pedersen M. W.,
Barnes D. K.
Publication year - 1965
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1965.0011183x000500010002x
Subject(s) - downy mildew , agricultural experiment station , geneticist , library science , inheritance (genetic algorithm) , resistance (ecology) , mildew , agriculture , genealogy , history , biology , horticulture , computer science , agronomy , archaeology , genetics , gene
DOWNY mildew (caused by Peronospora trifoliorum DBy) is widely distributed on alfalfa (Medicago sativa L.) throughout temperature areas of the world. While seldom a serious disease in northern United States, downy mildew is usually present and may cause significant leaf drop and s,.~edling damage during cold, wet weather. Damage is usually confined to the first hay cutting. Most Utah fields have only a trace of infection, but occasional fields with severe foliage damage occur. Crall (1) included downy mildew as one of the serious diseases of alfalfa in Iowa and. Fenne et al. (2) observed many infected fields in Virginia. According to Jones and Smith (4) the pathogen probably overwinters in alfalfa crown-buds, which serve as the primary source of infection the following spring. Oospores are found in the leaves, but germination of these has not been observed. Infected leaves turn pale green on the upper surface, then yellow, and drop prematurely. Sporulation occt~rs on the underside of the leaf where a profusion of mycelia develop. No biological races of the fungus have been distinguished on alfalfa. Smith (5) studied seedlings from 17 strains and 4 varieties of alfalfa fi)r downy mildew resistance. Infected plants ranged from 4.5 to 32.1%. The percentage of infected plants in the 4 varieties was: ’Grimm’, 9.6; ’Ladak’, .13.6; ’Buffalo’, 15.0; ~tnd ’Ranger’, 15.2’%. Jones and Smith (4) suggested that susceptibilit~ behaved as a dominant character and that approximately one-fourth of the plants from common varieties are susceptible to the disease. However, the senior author of this paper has observed certain strains of ’Hairy Peruvian’ alfalfa that are almost completely susceptible. Stanford (6) introduced dow~y mildew resistance into California Common alfalfa in the third backcross for bacterial wilt resistance. This was followed by one additional generation of backcrossing and one of selfing. In an artificial inoculation, test, 89% of California Common plants and 6.5’% of the new variety ’Caliverde’ became infected. The present ~,;tudy reports segregations for downy mildew resistance that were observed in the S~., F~, Fe, and backcross generations of a cross between resistant and susceptible parents. A hypothesis for the inheritance of downy mildew resistance in alfalfa is presented.