1318 Utilization of Resistance and Tolerance to Root-Knot Nematode in Cotton

The southern root-knot nematode, Meloidogyne incognita, is the most damaging pathogen of cotton in the USA. Host-plant resistance to root-knot nematodes is an effective means of reducing crop losses and reducing nematode population levels in a field. Resistance to plantparasitic nematodes refers to the suppressive effect of the plant on the nematode’s ability to reproduce; tolerance describes the degree of damage caused by the nematode to the plant. Resistance to root-knot nematodes in cotton is correlated with tolerance, so crop loss decreases as the level of resistance increases. Cotton genotypes with the highest yield in the absence of nematode damage tend to have greater percentage losses when damaged by nematodes because nematodes prevent the plant from fully exploiting favorable growing conditions. Consequently, effective nematode management is increasingly important and beneficial in genotypes with the highest yield potentials. When either moderately resistant or highly-resistant cotton is grown, for one or more years, root galling and nematode population densities in the soil are significantly lower compared to a susceptible standard. Development of host-plant resistance to M. incognita in cotton using traditional breeding techniques has been difficult because it is very labor intensive and involves multiple resistance genes. Recent advances in identification of DNA markers for nematode resistance genes shows great promise, and should lead to the rapid development of resistant genotypes. Limited sources of resistance genes may increase selection pressure on nematode populations and lead to loss of efficacy of resistance genes.