Impact of Planting RKN-Susceptible Variety after Multi-Year Plantings of RKN-Resistant Variety in Cotton

Our studies involving recombinant inbred lines have indicated ~10-20% yield gain in the resistant lines over the susceptible lines.  However, if a grower decides to plant a susceptible variety on a field that was planted with a resistant variety for a few consecutive years then the logical question to ask is what are the implications of that decision on yield and nematode populations on that field that given year?  In this study, we try to seek answers to that question.  Yield and RKN phenotypic (early in the season & at harvest) data were collected on a susceptible variety (DP1044 B2RF) planted on resistant- variety and susceptible-variety planted blocks for four consecutive years in a high RKN pressure field (Tahoka, TX).  Results indicate 93% fewer RKN eggs collected early (54 DAP) in the season which translated into 60% yield gain in the resistant-variety planted block over the susceptible-variety planted block for the same susceptible variety.  However the soil sample data collected at harvest showed no difference in the RKN juveniles between the resistant-variety and susceptible-variety planted blocks indicating bounce back in RKN numbers in the resistant-variety planted block in just in one year of planting susceptible variety.  In conclusion, planting of a susceptible variety on a field planted with resistant variety for four consecutive previous years can provide grower a significant yield gain compared to the susceptible-variety planted field due to low RKN pressure early in the season for the resistant- variety planted field. In this study, however, it only took one season of planting a susceptible variety for the RKN populations in the resistant-variety planted field block to bounce back to the levels observed in the susceptible-variety planted field block.