The effects of nutrient availability on the host plant resistance of gerbera to western flower thrips

Nutrition of host plants has been shown to have a direct effect on the productivity of numerous insect pests, including western flower thrips [(WFT) Frankliniella occidentalis (Pergande)] ? a major pest on both horticulture and agronomic crops. Plants use constitutive and induced chemical defenses to aid in protection against phytophagous insects. Reductions in WFT abundance in response to decreased nutrient availability has been attributed to the reduced availability of nutrients required for WFT productivity. The goals of this research were to determine the effects of fertilization on chemical defenses, and subsequent effects on WFT feeding and abundance. More importantly, the effects of fertilization and WFT feeding on plant growth, development, physiology, and quality were determined to assess the viability of optimizing fertilization in order to increase host plant resistance in gerbera. Constitutive (i.e. phenolics) and induced (i.e. jasmonic acid) chemical defenses were enhanced when fertilization was reduced. Reducing fertilization increased the total phenolics and wound- and WFT-induced jasmonic acid (JA) accumulation in gerbera. The enhanced chemical defenses in lower fertility plants resulted in reduced WFT abundance and feeding damage. These results indicate that the strategy for some plant species under nutrient stress is to increase constitutive defenses, while maintaining, or possibly increasing inducible defenses instead of growth. Similar to 0X fertility plants (only supplied with initial fertilizer charge in commercial media), 0.3X (received 30% of recommended rate) gerberas had reduced biomass and greater chemical defenses compared to 1X plants, but these plants did not appear to be nutritionally stressed?and 0.3X plants without WFT were rated as marketable. Reducing fertilization by 70% (0.3X) did not affect flower dry mass (DM) or the rate of flowering, but the flower stalks (peduncles) were taller in response to the fertilizer reduction. Hence, reducing fertilization to a moderate level in gerbera production may reduce susceptibility to WFT, while producing marketable crops.