SUSCEPTIBILITY OF GRAIN SORGHUM CULTIVARS TO MELOIDOGYNE INCOGNITA IN LOUISIANA, USA

Greenhouse studies were conducted to evaluate the host suitability of cultivars of sorghum currently grown in Louisiana to Meloidogyne incognita. A total of 29 cultivars of grain sorghum were evaluated. Nematode reproduction was highly variable among the cultivars of sorghum tested and ranged from 1,239 to 30,440 eggs/g of root and from 1,440 to 25,208 J2/500 cm(3) soil on REV RV9782 and DeKalb DKS 53-67 cultivars, respectively. A second study was conducted to determine the influence of 10 populations of M. incognita from Louisiana on Dekalb DKS 53-67, REV RV9924, and REV RV9782 sorghum, rated as being susceptible, moderately susceptible, and moderately resistant, respectively. Sorghum cultivar and root-knot nematode population significantly affected nematode reproduction in a greenhouse environment. As previously determined, DEKALB DKS 53-67 was the most susceptible and REV RV9782 the least susceptible across the 10 populations of M. incognita. Across the three cultivars of sorghum, there was significantly greater reproduction by the M. incognita population from St. Landry (LARK19) than the other 9 populations. There was a significant sorghum cultivar by nematode population interaction, which influenced the number of eggs/g of root. There were significant differences in egg production among the different populations of M. incognita on the cultivars DEKALB DKS 53-67 and REV RV9924. Despite the great variability in reproduction and broad geographical distribution of the nematode populations, no intraspecific variation of 18S and 28S ribosomal DNA was observed among them. Egg production on the resistant cultivar REV RV9782 was similar across all populations of M. incognita. This research highlights the need to evaluate sorghum cultivars within a geographical location for susceptibility to M. incognita.