Simulation of early season herbivory via mechanical damage affects flower production in pumpkin (Cucurbita pepo ssp. pepo)

Abstract

Background: Damage from insect herbivores can elicit a wide range of plant responses, including reduced or compensatory growth, altered volatile profiles, or increased production of defence compounds. Specifically, herbivory can alter floral development as plants reallocate resources towards defence and regrowth functions. For pollinator-dependent species, floral quantity and quality are critical for attracting floral visitors; thus, herbivore-induced developmental effects that alter either floral abundance or attractiveness may have critical implications for plant reproductive success. Based on past work on resource trade-offs, we hypothesize that herbivore damage-induced effects are stronger in structural floral traits that require significant resource investment (e.g. flower quantity), as plants reallocate resources towards defence and regrowth, and weaker in secondary floral traits that require less structural investment (e.g. nectar rewards).

Methods: In this study, we simulated early-season herbivore mechanical damage in the domesticated jack-o-lantern pumpkin Cucurbita pepo ssp. pepo and measured a diverse suite of floral traits over a 60-d greenhouse experiment.

Key results: We found that mechanical damage delayed the onset of male anthesis and reduced the total quantity of flowers produced. Additionally, permutational multivariate analysis of variance (PERMANOVA) indicated that mechanical damage significantly impacts overall floral volatile profile, though not output of sesquiterpenoids, a class of compounds known to recruit specialized cucumber beetle herbivores and squash bee pollinators.

Conclusions: We show that C. pepo spp. pepo reduces investment in male flower production following mechanical damage, and that floral volatiles do exhibit shifts in production, indicative of damage-induced trait plasticity. Such reductions in male flower production could reduce the relative attractiveness of damaged plants to foraging pollinators in this globally relevant cultivated species.

Keywords: Cucurbita pepo ssp. pepo; Cucurbitaceae; energetic trade-offs; floral traits; greenhouse experiment; phenology; simulated herbivory.

Graphical Abstract

Fig. 1.

Mean day of first male flower produced by C. pepo ssp. pepo plants subjected to control (0 %), moderate (15 %) and extreme (50 %) levels of mechanical damage by leaf area removal in simulated herbivory treatments. Error bars represent standard error of the mean. Letters above error bars indicate significant differences between treatments (α = 0.05).

Fig. 2.

Cumulative number of male flowers produced by C. pepo ssp. pepo plants subjected to control (blue, 0 %), moderate (yellow, 15 %) and extreme (red, 50 %) levels of leaf area removal mechanical damage in simulated herbivory treatments. Error bars represent standard error of the mean of each 5-d interval. Asterisks above error bars indicate significant differences between treatments tested at each interval (α = 0.05).