Resistance to Rotylenchulus reniformis and Meloidogyne incognita Race 3 in the Major Cotton Cultivars Planted Since 1950

Abstract

The southern root-knot nematode, Meloidogyne incognita race 3 (Kofoid & White) Chitwood, and the reniform nematode, Rotylenchulus reniformis Linford & Oliveira, are the most widespread and economically important nematode pests of Upland cotton (Gossypium hirsutum L.) and Pima cotton (G. barbadense L.) in the USA. Progress in the development of nematode-resistant cotton cultivars is unclear. Plant breeders often have selected for nematode tolerance by measuring cotton yield in nematode-infested fields but seldom have selected for resistance by measuring nematode reproduction. The objective of this research was to measure nematode reproduction to assess progress in the development of nematode resistance in cotton. Fiftyfive Upland and four Pima cotton cultivars, comprising the most widely planted cultivars in the USA each decade since 1950, were evaluated in growth chambers for resistance to M. incognita and R. reniformis. The cultivar Deltapine 16 served as the susceptible and the germplasm line Auburn 623 RNR as the resistant control. Reproduction by M. incognita on the cultivars ranged from 4 to 294% of that on Deltapine 16. All cultivars were highly susceptible to R. reniformis. A small increase was detected in the general level of resistance to M. incognita between 1950 and 1996, but only the recently released cultivars, Stoneville ‘LA887’, Paymaster ‘1560’, and CPCSD ‘Acala Nem-X’, showed consistently high resistance. These cultivars were developed by measuring nematode reproduction in pots or root galling in field plantings, as well as yield and related agronomic traits.