LONREN UPLAND COTTON GERMPLASM RESPONSE TO ROTYLENCHULUS RENIFORMIS INOCULUM LEVEL

Sikkens, R. B., D. B. Weaver, K. S. Lawrence, S. R. Moore and E. van Santen. 2011. LONREN Upland Cotton Germplasm Response to Rotylenchulus reniformis inoculum level. Nematropica 41: 68-74. Rotylenchulus reniformis (reniform nematode) can be a yield-limiting factor for upland cotton. Resistance to this nematode was discovered in a wild cotton relative, transferred to an upland background and released as the germplasm LONREN. The LONREN source of resistance to reniform nematode in upland cotton was evaluated for reaction to increasing levels of inoculum on root and shoot growth and nematode reproduction compared to susceptible genotypes. Genotypes tested were LONREN-1 and LONREN-2 (resistant); Fibermax 966 and Deltapine 555BR (susceptible); and one susceptible and one resistant F2:4 line from the cross LONREN-1 × Fibermax 966. Inoculum levels of 0, 500, 1000, 5000, 10,000, or 50,000 juveniles and vermiform of R. reniformis were used. Plant height and vigor ratings were collected weekly. Root and shoot fresh and dry mass, and nematode numbers were collected 60 days after inoculation. Based on inoculation rate, a reproduction factor (Rf) was calculated as the ratio Pf/Pi, where Pf = final nematode population and Pi = initial inoculum level. Root dry mass of genotypes with the LONREN resistance source was reduced at high inoculation density compared to low inoculum levels. An opposite trend was observed for root dry mass of reniform nematode susceptible genotypes, where root dry mass increased at higher inoculum levels. Shoot dry mass for all genotypes was largely unaffected except at the highest inoculum level. Shoot to root dry mass ratios for the LONREN resistance source genotypes were found to trend higher with increased inoculum levels, whereas the same ratios decreased in case of the susceptible genotypes. Examination of the roots of LONREN resistant source genotypes showed signs of necrosis. We conclude that the LONREN resistance source exhibits a type of hypersensitive response to reniform nematode. This reaction, while inhibiting reniform nematode reproduction, appears to be a factor in seedling stunting at higher nematode density levels. Sikkens, R. B., D. B. Weaver, K. S. Lawrence, S. R. Moore and E. van Santen. 2011. LONREN Upland Cotton Germplasm Response to Rotylenchulus reniformis inoculum level. Nematropica 41: 68-74. Rotylenchulus reniformis (nematodo reniforme) puede ser un factor limitante en la produccion de algodon. Se descubrio resistencia a este nematodo en parientes silvestres del agodon y se transfirio dicha resistencia al algodon cultivado para crear el germoplasma LONREN. En este trabajo, evaluamos la reaccion del germoplasma a diferentes niveles de inoculo de nematodo reniforme. La reaccion se midio en terminos de crecimiento de raices y brotes y reproduccion del nematodo. Se evaluaron los genotipos LONREN-1 y LONREN-2 (resistentes); Fibermax 966 y Deltapine 555BR (susceptibles); y una linea F2:4 susceptible y otra resistente del cruce LONREN-1 × Fibermax 966. Se usaron niveles de inoculo de 0, 500, 1000, 5000, 10,000 o 50,000 juveniles y vermiformes de R. reniformis. Se midio la altura y el vigor de las plantas cada semana. El peso seco y fresco de raices y brotes se midio 60 dias despues de la inoculacion. El factor de reproduccion (Rf) se calculo usando Pf/Pi, en donde Pf = poblacion final del nematodo y Pi = nivel de inoculo inicial. Se observo una reduccion en la masa seca de raices de los genotipos con resistencia LONREN con los niveles de inoculo mas altos. En los genotipos susceptibles, se observo la tendencia contraria, con un incremento de la masa de raices con los niveles de inoculo mas altos. No se observo efecto sobre la masa seca de los brotes, excepto con los niveles de inoculo mas altos. Se encontro que la relacion masa seca de brotes sobre masa seca de raices aumento con el nivel de inoculo para los genotipos LONREN, mientras que esta relacion disminuyo en el caso de los genotipos susceptibles. Se encontro necrosis en las raices de los materiales LONREN. Concluimos que la fuente de resistencia LONREN muestra un tipo de resistencia hipersensible al nematodo reniforme. Esta reaccion inhibe la reproduccion del nematodo reniforme, pero tambien parece ser un factor en el pobre desarrollo de las plantulas a altos niveles de inoculo.