Canonical discriminant analysis of Rotylenchulus reniformis in Alabama

The reniform nematode, Rotylenchulus reniformis, infests over 300 plant species worldwide and over the last two decades it has emerged as a major cotton pest in the southeastern United States. Nine locations in Alabama and one location in Mississippi were selected for study of R. reniformis. Thirteen morphometric measurements were made on 20 male and 20 female nematodes from each population. The sex and location interaction was significant (P < 0.005) for all traits except total body length (P = 0.29) and the derived ratio trait a (body length / maximum body width, P = 0.06). Canonical discriminant analysis effectively separated the 10 sampling locations into three distinct groups; among them, Group 1 and 3 were distinct with an intermediate group (Group 2) differentiating in the middle. Furthermore, both female and male R. reniformis based on the morphometrics measured here adhered to this metrics-based grouping. Belle Mina (Limestone County, AL), Huxford (Escambia County, AL), and Mississippi State University, MSU (Oktibbeha County, MS) locations were separated from the remaining seven locations based on the large positive CAN1 centroid means. Eight out of 13 traits had high phenotypic correlations (r > 0.80) with CAN 1 for both sexes. Anal width and length of the hyaline portion of the tail measurement accounted for a significant amount (r > 80%) of the variation in total and sex-based canonical structure. Occurrence of the three non-overlapping morphometric groups in cotton-growing fields in close proximity (250 mile radius) suggests a greater biological variation in this species than expected. Cotton cultivars with differential resistance and soil types are among the major factors to be tested for further delineating the causes of morphometric variation in R. reniformis.