Reproduction and pathogenicity of native isolates of Rotylenchulus reniformis, from Louisiana on soybean

The reniform nematode (Rotylenchulus reniformis) is one of the major pests on both soybean and cotton in the south. Although there are resistant soybean cultivars available, this resistance may not be consistent with different geographical isolates of the pathogen. Experiments were conducted to evaluate soybean responses to indigenous isolates of the reniform nematode in Louisiana on commercial cultivars and resistant germplasm lines. Microplot and greenhouse experiments were conducted during 2016 and 2017 to evaluate the comparative reproduction and pathogenicity of isolates of R. reniformis isolated from West Carrol (WC), Rapides (RAP), Tensas (TEN) and Morehouse (MOR) parishes of Louisiana. Prior to the experiments single egg-mass populations of each geographic isolate were increased on tomato under greenhouse condition. Data from full-season microplot studies, averaged over 2 trials, showed significant differences of the nematode in both reproduction and pathogenicity with the commercial cultivars REV 56R63, Pioneer P54T94R, and Dyna-Gro 39RY57. There was a significantly lower population density with the isolate from MOR representing a 46% reduction in numbers compared to the isolate from the WC parish. The MOR isolate was also the most pathogenic and resulted in soybean plant and pod weights 30 and 44% lower, respectively compared to the noninoculated. Data from 60 day greenhouse experiments averaged over two trials reflected a similar trend to that of the microplot trials. In these trials the susceptible cultivar Progeny P4930LL and the resistant germplasm lines PI 90763 and PI 548316 were tested together with the same cultivars used in the microplot trials. Similar to the microplot trials, the MOR isolate had the lowest level of reproduction with a 33% reduction in life stages in soil compared to that of WC, the isolate with the greatest level of reproduction. This trend in reduction was more evident when determining the numbers of eggs per root system with a 50% reduction from MOR compared with WC. In microplot and greenhouse trials, the soybean cultivar REV 56R63 had a significant reduction in reniform numbers in soil compared to cultivars Pioneer P54T94R, and Dyna-Gro 39RY57 by contributing to a 45% and 70% reductions in soil density respectively. In the greenhouse trials REV 56R63 showed a pronounced resistant against all nematode isolates when compared to the moderately resistant germplasm line PI 548316. The resistant germplasm line PI 90763 was able to hold its resistance compared to tested cultivars and germplasm lines against all isolates of the reniform nematode. Data from these experiments add further evidence to the contention that there are virulence phenotypes of R. reniformis