Geographic isolates of reniform nematode differ in their reproduction and virulence

Management of the reniform nematode (Rotylenchulus reniformis Linford and Oliveira) in upland cotton (Gossypium hirsutum L.) continues to be a challenge primarily due to inconsistent performance of resistant genotypes. We hypothesize that diversity in reproduction and virulence in R. reniformis has contributed to the inconsistent performance of resistant cotton genotypes. Rotylenchulus reniformis isolates from Tennessee (TN), Alabama (AL), Mississippi (MS), Texas (TX), Louisiana (LA), Arkansas (AR), Florida (FL), South Carolina (SC) and Georgia (GA) were assessed for their reproduction and virulence on a resistant cultivar DP 2141NR B3XF and a susceptible cultivar DP 2317 B3TXF. The AR isolate had the greatest reproduction factor (Rf) of 19.7, while the AL isolate had the least Rf of 3.3. Rfs of other isolates were intermediate. Up to 85% of reproductions were suppressed by the resistant cultivar relative to the susceptible cultivar. While plants inoculated with nematodes had lower root biomass than the non-inoculated control, the degree of root biomass reduction varied by isolate, suggesting differing levels of virulence among R. reniformis isolates. The AR isolate reproduced the most and was the most virulent. The AL isolate reproduced the least and was less virulent. The AR, MS, TN and LA isolates were the top four reproducing isolates, probably indicating a greater suitability of the Delta region for nematode reproduction. The correlation analysis indicated that up to 85% variation in plant biomasses was explained by nematode reproduction. These results suggest that resistance breeding programs in cotton must consider the diversity in R. reniformis.