Studies on interspecific hybridization of Meloidogyne chitwoodi and M. fallax: they are two different specie
Until recently, Meloidogyne chitwoodi (EPPO A2 quarantine pest) and M. fallax were considered as a single species (M. fallax was referred to as M. chitwoodi type Baexem). But morphological, biological, molecular differences were observed and suggested that they were two different species (EPPO RS 97/001). Studies were carried out in the Netherlands to verify their reproductive isolation. In M. chitwoodi and M. fallax, reproduction is characterized by facultative meiotic parthenogenesis (amphimixis and meiotic parthenogenesis can occur). Amphimixis may result when insemination by males occurs. Two types of experiments were done: 1) controlled cross between the two species; 2) bulk mating in a 1:1 mixture of two isolates of the two species. In these studies, all isolates used had the same number of chromosomes (no data is available on crossings between isolates with different numbers of chromosomes). During the first type of experiment, successful hybridization was obtained and hybrid females (F1) were able to produce egg masses. However, the hatched F2 juveniles were small in numbers, with morphological distortions and were non viable. In the bulk mating experiment, the progeny contained parental-type females of the two isolates in equal numbers and 10% of all females were non-viable hybrids. This study supports the separate species status of M. chitwoodi and M. fallax, as the progeny of their interspecific hybrids is non-viable. The authors also noted that this is the first report of interspecific hybridization in Meloidogyne.
Sources
van der Beek, J.G.; Karssen, G. (1997) Interspecific hybridization of meiotic parthenogenetic Meloidogyne chitwoodi and M. fallax.
Phytopathology, 87(10), 1061-1066.