Morphological variability in second-stage juveniles and males of Meloidogyne chitwoodi

Abstract

The morphology of Meloidogyne chitwoodi is relatively poorly characterised. In a recent study, morphological variation in adult females of M. chitwoodi was analysed. However, comparable data are lacking for adult males and second-stage juveniles (J2). Therefore, our studies of four M. chitwoodi isolates from the western USA, representing all currently known races and pathotypes, were designed to characterise intraspecific morphological variability in J2 and males and to compare it to variability found in adult females. Multivariate analysis of variance indicated statistically significant variation among isolates for both J2 and males. Moreover, for adult males, canonical discriminant analysis grouped races with their respective pathotypes. In addition, we analysed two morphological features that were previously uncharacterised for M. chitwoodi, i.e., stylet knob width and distance from secretory-excretory pore to anterior end. Both of these characters may be useful in distinguishing M. chitwoodi from closely related species. SEM clearly showed the presence of areolations along the bodies of J2, thereby separating M. chitwoodi from M. fallax and M. minor. In summary, this study indicates that M. chitwoodi J2 and adult males show substantially more intraspecific morphological variability than previously known. Consequences for diagnostics are discussed.