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

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Abstract
The fusarium wilt fungus, Fusarium oxysporum Schlect f. vasinfectum [(Atk.) Synd.& Hans.], and the root‐knot nematode (RKN) [Meloidogyne incognita (Kofoid & White) Chitwood] cause a destructive disease complex in cotton (Gossypium hirsutum L.). This study was conducted to determine the range of genetic resistance to RKN in a group of 18 cotton cultivars and breeding lines, to evaluate the relationship between genes for resistance to fusarium wilt disease (FW) and the genes for RKN resistance, and to ascertain the relative importance of the two types of resistance in controlling FW. Numbers of RKN eggs produced on the cottons ranged from 148 000/plant on ‘Rowden’. One‐eighth as many and 18 times more RKN eggs/plant were produced on Auburn 623 RNR and Rowden in 40 days, respectively, than were used to inoculate them. No commercial cultivar was resistance to RKN in this study. Two cotton cultivars expressed genetic resistance that provided moderate field resistance to FW independently of RKN resistance. Differences in resistance to FW in the field among cotton cultivars and breeding lines were determined more by RKN resistance than by genetic resistance to FW. Results indicate that cotton can be developed with genetic resistance to FW independently of RKN resistance and that this genetic resistance probably would provide moderate field resistance to FW. High field resistance to the RKN‐FW complex depends on high RKN resistance, and cotton cultivars with high RKN resistance probably would have adequate field resistance to this complex even if they were genetically susceptible to FW.