Reniform Nematode Resistance in Upland Cotton Germplasm

Cotton (Gossypium spp.) is attacked by parasitic nematodes including the reniform nematode (Rotylenchulus reniformis Linford and Oliveira). Options for management of reniform nematode are limited. No cultivars of upland cotton (G. hirsutum L.) have genetic resistance. Our objectives were to evaluate the USDA G. hirsutum collection for reaction to parasitism by R. reniformis, and determine the value of measurement of eggs (reproduction) or vermiform stages (nematode survival) as an indicator of nematode resistance. In groups of 50, accessions were evaluated in the greenhouse, using single plants in four replicates. Accessions were planted in sterile soil and inoclated with a mixture of R. reniformis isolates. After 60 d, soil populations of vermiform nematodes were determined, and eggs were extracted from the root system and counted. Paymaster 'PM 1218' was included as a check in every experiment. Out of 1973 accessions with at least one replication, none showed high levels of resistance. Seven accessions had lower population development than PM 1218 after repeated evaluations. Results indicated egg counts and vermiform counts were correlated, but not closely. Egg counts were higher and more variable than vermiform counts. While some accessions showed levels of resistance that might be useful in cotton improvement, evaluation remains difficult and introgression of genes for reniform nematode resistance remains a long-term breeding objective.