PLANT-AGE AND SEASONAL-VARIATIONS IN GENOTYPIC RESISTANCE OF CELERY TO BEAT ARMYWORM (LEPIDOPTERA, NOCTUIDAE)

Plant physiological growth stage and growing environment significantly interacted with celery (Apium graveolens L.) genotypes to influence the expression of genetic resistance of celery to the beet armyworm, Spodoptera exigua (Hubner). Plant vegetative growth, as measured by plastochron index, was primarily linear with physiological time and showed no major season-related variations. Insect developmental times from egg to pupa and from egg to adult showed the largest variations during this study, with significant genotype-by-season, genotype-by-plant growth stage, and season-by-stage interactions. Overall, all four celery genotypes tested, 'Tall Utah 52-70R', 'UC-08', 'UC-10', and 'UC-26', were more resistant to beet armyworm during the warm season and as plants matured. Because both plant age and growing environment proved to interact significantly with plant genotype to magnify or suppress expression of genetic plant resistance to pests, it is important to study test plant genotypes under various growing conditions and at different stages of plant growth to determine the potential genotype-by-environment and genotype-by-stage interactions before characterization and utilization of the resistance in breeding for pest resistance and integrated pest management programs.