The southern root-knot nematode, Meloidogyne incognita race 3 (Kofoid & White) is a widespread pathogen of Upland cotton (Gossypium hirsutum
L.) in the United States. Progress in the development of productive cultivars in root-knot infested soils is dependent upon the identification of germplasm sources containing genes conferring resistance and/or tolerance this pest. The objective of this research was to screen 150 accessions from the Texas Race Stock collection previously uncharacterized for their reaction to the root-knot nematode. This was done in a sick plot nursery by rating the degree of galling present. Of the 150 accessions evaluated, 146 were rated at maturity using an indexed scoring system ranging from 0 (no galling present) to 5 (severe galling). The range of galling scores was from
1.7 – 5.0 with a mean of 3.75. The average gall score of the resistant check, Stoneville LA887, was 2.04. Twenty-four accessions had galling index scores of less than 3 with two having index scores less than the resistant check. A total of 15 percent of the accessions flowered during the traditional growing season at the Red River Research Station. Two of the flowering accessions had galling scores not significantly different from the resistant check. These are from Thailand and India, countries outside the center of diversity for Upland cotton, indicating that useful diversity can arise outside of germplasm centers.