Trends in the proportion of female white-tip nematode Aphelenchoides besseyi during rice growth stages

Summary Adults of Aphelenchoides besseyi , a rice-infecting parasite, are characterised by a high female-to-male ratio and it is thought that the high concentration of females among the seeds makes it advantageous for mating. However, the relationship between A. besseyi density within the glume of rice plants and changes in the proportion of females has yet to be determined. This study examines the annual variation in the proportion of adult females that invade the glume according to the stage of rice growth. Field observations performed to assess annual and growth stage-related variations in female nematode proportions and population densities at different rice growth stages revealed no significant differences in the proportions of live, dead or total female nematodes during the period between 2003 and 2020. However, total nematode counts per seed increased in the following order: heading stage < dough-ripe stage < yellow ripe stage < maturing stage. Furthermore, the proportion of females was found to be higher during the dough-ripe stage than during the yellow ripe stage, and in seeds containing only female nematodes, the proportion of females with sperm in the spermatheca was similarly higher during the heading stage and the dough-ripe stage than during the yellow ripe stage and the maturing stage. The findings of this study indicate that mated adult females of A. besseyi containing sperm in their spermatheca invade rice spikelets during the heading stage. In addition, the population of adult males increases as rice matures, thereby maintaining a female to male ratio of approximately 0.8.