Comparisons of Female and Egg Assays to Identify Rotylenchulus Reniformis Resistance in Cotton

Authors: Stetina, Salliana - Sally; Young, Lawrence

Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/2006
Publication Date: 9/1/2006
Citation: Stetina, S.R., Young, L.D. 2006. Comparisons of Female and Egg Assays to Identify Rotylenchulus Reniformis Resistance in Cotton. Journal of Nematology. 38:326-332

Interpretive Summary: The reniform nematode (Rotylenchulus reniformis) has become a major root pathogen of cotton in the Mid South area of the United States. Tests for resistance to this pathogen are important in cotton variety development. As the reniform nematode develops, females feed on the roots of the plant and later begin laying eggs. Because adult females must develop before eggs can be produced, a reliable test based on females would shorten the time involved and allow more plants to be evaluated for resistance to the nematode each year. In this study, it was demonstrated that assessments based on female counts generated the same results as assessments based on egg counts, indicating that the two life stages can be used interchangeably to screen for resistance to the nematode. Furthermore, it was determined that approximately 40% more plants can be assessed per year if females are counted instead of eggs. The rapid, reliable screening method based on females will be a useful tool for cotton breeders as they develop cultivars with resistance to this important pest.

Technical Abstract: More plants can be screened for reniform nematode resistance each year if the time involved can be shortened. In this study, the hypothesis that female counts are as efficient as egg counts in identifying resistant genotypes was tested. In two greenhouse experiments Gossypium genotypes which varied from resistant to susceptible to reniform nematode were compared to a susceptible control cultivar. Infested field soil served as the inoculum source for the first experiment, and vermiform stages extracted from greenhouse cultures were used to infest soil in the second experiment. Six replicates of each genotype were harvested 25 days after planting and swollen females were counted. The remaining plants were harvested 35 days after planting and eggs extracted from the roots were counted. Processing and counting times recorded in the first experiment were similar for both assessment methods, but 10 additional days were required for egg-based assessment. Contrast analyses showed that assessments based on females per gram of root were equivalent to assessments based on eggs per gram of root for the five varieties tested in the first experiment and for an expanded set of 13 genotypes tested in the second experiment. This indicates that either life stage can be used to screen for resistance.