PATHOGENICITY AND REPRODUCTION OF ISOLATES OF RENIFORM NEMATODE, ROTYLENCHULUS RENIFORMIS, FROM LOUISIANA ON SOYBEAN
The reniform nematode (Rotylenchulus reniformis) is one of the major pests on both soybean and cotton in the southern United States. Although resistant soybean cultivars are available, this resistance may not be uniform across geographical isolates of the pathogen. Experiments were conducted to evaluate responses of indigenous isolates of reniform nematode in Louisiana on commercial soybean cultivars and resistant germplasm lines. Experiments in greenhouse and microplot environments were conducted during 2016 and 2017 to evaluate the comparative reproduction and pathogenicity of populations of R. reniformis isolated from West Carroll (WC), Rapides (RAP), Tensas (TEN), and Morehouse (MOR) parishes of Louisiana. Data from full-season microplot studies, averaged over 2 trials, showed differences in reproduction and pathogenicity of the nematode on REV 56R63, Pioneer P54T94R, and Dyna-Gro 39RY57 soybean cultivars (P<0.01). Reproduction by the MOR isolate was 46.8% lower than that by the WC isolate. However, the MOR isolate was the most pathogenic isolate with 20.8% lower plant and 44.6% lower pod weight compared to the non-inoculated control. Data from 60-day duration greenhouse experiments reflected a similar trend. In greenhouse trials, the susceptible cultivar Progeny P4930LL and the resistant PI lines 90763 and 548316 were included with the cultivars employed in the microplots. Reproduction by the MOR isolate was 33% less than that by WC isolate. Reduced reproduction by the MOR isolate relative to the WC isolate was accounted for by a 50% reduction in the numbers of eggs per root system. In both microplot and greenhouse environments, REV 56R63 was a significantly less suitable host for reniform nematode than was Pioneer P54T94R, Dyna-Gro 39RY57, and PI 548316.