Evidence of sexual reproduction events in the dagger nematode Xiphinema index in grapevine resistance experiments under controlled conditions

The dagger nematode Xiphinema index has a major economic impact due to its transmission of Grapevine fanleaf virus (GFLV) to grapevines. This vector nematode, which was introduced into Western countries from the Middle East together with the domesticated grapevine, mostly reproduces by meiotic parthenogenesis, but microsatellite multilocus genotype (MLG) analysis has revealed the occurrence of rare sexual reproduction events in field conditions. In a previous six-year study under controlled conditions, we evaluated the durability of resistance (R) to X. index in accessions derived from a muscadine R source and reference accessions. In this previous study, we used an equal-proportion mixture of four lines (from Spain, Italy, Greece and Iran) representative of X. index diversity as the inoculum, and we collected random samples in three-, four-, five- and six-year-old vines. Here, we genotyped the individuals from these samples using MLG technique, and we analyzed the changes in line frequency and the occurrence of sexual reproduction events between lines over time. The nematode lines differed in aggressiveness and hybrids between lines were detected at a low, but apparently increasing rate. Hybridization events were recovered in all accessions, regardless of resistance status and propagation type. Finally, our data provide the first evidence of sexual reproduction in the nematode X. index under controlled conditions.