Breeding for Disease Resistance in Cucurbits

Abstract

Members of the Cucurbitaceae are among the important and widespread plants that supply man's food and fiber. Cucurbits are not as important on a world basis as are cereals and legumes, but, from the tropics to the milder portions of the temperate zone, they serve as a source of carbohydrates, as dessert and salad ingredients, and as pickles. Some cucurbits are used as pot­ tery, baskets, insulation, and oil filters. The cultivated cucurbits have needed man for survival since bona fide specimens of the wild counterparts of the cultivated species have apparently never been collected. Although there are about 90 genera and 750 species in the family Cucur­ bitaceae, only 6 genera and 12 species are cultivated by man. These genera and species include watermelon (Citrullus); cucumber, muskmelon, and gherkin (Cucumis); dish-rag and sponge gourds (Luffa); white-flowered gourd (Lagenaria); squashes, marrow, pumpkin, and figleaf gourd (Cucur­ hila); and chayote (Sechium). All the species are frost-sensitive. Within each species there is a wide assortment of sizes, shapes, color variants, flesh tex­ tures, flavors, etc (62). The use of resistant varieties is a simple, effective, and economical means of controlling plant disease (45). A large number of disease resistance fac­ tors have been incorporated into cultivated cucurbits, particularly during the past 30 years. Associated with this has been the development of specific desir­ able horticultural characteristics. These two objectives are inseparable, as it is a bounteous yield of attractive, high quality fruits that is demanded by the consumer. In the present era, cucurbits are being produced commercially in areas where they could not be produced previously because of disease; vari­ eties with resistance to one disease have been replaced by varieties with resis­ tance to many diseases; disease resistance has been a major factor in develop­ ment of mechanized harvesting; the high cost of disease control has been re­ duced; disease epidemics have been curtailed; and the use of resistant culti­ vars has diminished hazards and pollution resulting from use of potentially dangerous fungicides. It is with the theme of a breakthrough this discussion is concerned.