Effect of Soil Temperature on Reproduction of Root-knot Nematodes in Flue-cured Tobacco with Homozygous and/or Resistance Genes.

Most commercial flue-cured tobacco cultivars contain the resistance gene, which provides resistance to races 1 and 3 of and race 1 of . A number of cultivars now possess a second root-knot resistance gene, . High soil temperatures have been associated with a breakdown of root-knot resistance genes in a number of crops. Three greenhouse trials were performed from 2014 to 2015 investigate the effect of high soil temperature on the efficacy of and/or genes in reducing parasitism by a population of race 3. Trials were arranged in randomized complete block design in open-top growth chambers set at 25°, 30°, and 35°C. Plants were inoculated with 3,000 eggs and data were collected 35 days post-inoculation. Galling, numbers of egg masses and eggs, and reproductive index were compared across cultivar entries. Nematode reproduction was reduced at 25°C and 30°C on entries possessing and compared to the susceptible entry and the entry possessing only . However, there were often no significant differences in reproduction at 35°C between entries with and/or compared to the susceptible control, indicating an increase of root-knot nematode parasitism on resistant entries at higher temperatures. Although seasonal differences in nematode reproduction were observed among experiments, relative differences among tobacco genotypes remained generally consistent.