Cotton Resistance to the Root Knot‐Fusarium Wilt Complex. I. Relation to Fusarium Wilt Resistance and its Implications on Breeding for Resistance1

Abstract

Fusarium wilt disease (FW) caused by Fusarium oxysporum Schlect f. vasinfectum [(Atk.)Synd. & Hans.] and root‐knot nematodes (RKN) [Meloidogyne incognita (Kofoid and White) Chitwood] cause a major disease complex affecting cotton (Gossypium hirsutum L.). The purpose of this study was to determine the efficacy of using resistance to FW in the vascular system of plants grown in a greenhouse as a criterion for selecting cotton plants that are resistant to FW in the RKN‐FW complex as it occurs in the field. Eighteen cotton cultivars and breeding lines were inoculated in a greenhouse by injecting spores of the FW fungus directly into stems. Incidence of FW ranged from 29 to 82%. The FW percentages of the 18 cotton cultivars and lines in a field infested with both the fungus and RKN ranged from 3 to 99%. Results indicated that stem vascular resistance to FW was probably independent of any mechanism of resistance that might have prevented fungal invasion of the vascular system and that differences in vascular resistance were probably genetically controlled. Vascular resistance observed in the greenhouse failed to discriminate between differences in FW resistance among several cottons when grown in the field. This and other evidence presented indicated that a low probability of success would be expected for developing cotton cultivars with high field resistance to FW in the RKN‐FW complex by either selecting for vascular resistance expressed in plants grown in a greenhouse or through field selection by present techniques. Field selection for many decades had resulted in development of moderately resistant cultivars but had not been successful in developing highly FW‐resistant cultivars. Further progress by the field selection method may be possible in the future, if genes for higher resistance, such as in breeding line Auburn 623 RNR, are used and more precise screening techniques can be developed.