‘Resistance Mixtures’ Reduce Insect Herbivory in Strawberry (Fragaria vesca) Plantations

Abstract

The transition toward more sustainable plant protection with reduced pesticide use is difficult, because there is no “silver bullet” available among nonchemical tools. Integrating several plant protection approaches may thus be needed for efficient pest management. Recently, increasing the genetic diversity of plantations via cultivar mixing has been proposed as a possible method to reduce pest damage. However, previous studies have not addressed either the relative efficiency of exploiting cultivar mixing and intrinsic plant herbivore resistance or the potential utility of combining these approaches to increase cropping security. Here, using a full factorial experiment with 60 woodland strawberry plots, we tested for the relative and combined effect of cultivar mixing and intrinsic plant resistance on herbivore damage and yield. The experiment comprised two levels of diversity (“high” with 10 varieties and “low” with two varieties) and three levels of resistance (“resistant” comprising only varieties intrinsically resistant against strawberry leaf beetle Galerucella tenella; “susceptible” with susceptible varieties only; and “resistance mixtures” with 50:50 mixtures of resistant and susceptible varieties). The experiment was carried out over two growing seasons. Use of resistant varieties either alone or intermixed with susceptible varieties in “resistance mixtures” reduced insect herbivory. Interestingly, resistant varieties not only reduced the mean damage in “resistance mixtures” by themselves being less damaged, but also protected intermixed susceptible varieties via associational resistance. The effect of higher genetic diversity was less evident, reducing herbivory only at the highest level of herbivore damage. In general, herbivory was lowest in plots with high diversity that included at least some resistant varieties and highest in low diversity plots consisting only of susceptible varieties. Despite this, no significant difference in yield (fruit biomass) was found, indicating that strawberry may be relatively tolerant. Our results demonstrate that combined use of high genetic diversity and resistant varieties can help reduce pest damage and provide a useful tool for sustainable food production. “Resistance mixtures” may be particularly useful for sensitive food crops where susceptible varieties are high yielding that could not be completely replaced by resistant ones.

Bringing Fundamental Insights of Induced Resistance to Agricultural Management of Herbivore Pests

“…In particular, a diverse pollinator community will increase resilience in agricultural systems as the work of many pollinator species is complementary (Blüthgen and Klein 2011 ; Sapir et al 2017 ). By adopting more plant diversity on and surrounding agricultural fields (Balfour and Ratnieks 2022 ; Bänsch et al 2021 ; Koski et al 2021 ; Kovács-Hostyánszki et al 2017 ; Nicholls and Altieri 2013 ) and banning pesticide use, industrial agriculture can be transformed to have a more mutualistic interaction with wild pollinators and continue to benefit from their services (worth €153 billion (Gallai et al 2009 ).…”

“…Even more so, abiotic conditions such as water and nutrient availability may directly impact the vigour of inducibility of the crop, reducing crop potential to respond to herbivory. Crop mixtures and crop rotation strategies may be required to harness the resilience of a cropping system and promoting benefits of induced resistance (Koski et al 2021 ).…”

Effects of strawberry resistance and genotypic diversity on aphids and their natural enemies

“…Total yield per plot (fruit weight) was recorded for the months of May and June 2019. Ripe fruits were harvested on a weekly basis and fruits were weighed on the day of harvest (Koski et al, 2021).…”

“…New concepts such as cultivar mixing (Ninkovic et al, 2011) and resistance mixing (Koski et al, 2021) describe strategies that take advantage of intraspecific plant diversity to combat herbivory in crop plantations. However, relatively few studies have assessed the relative importance of resistance and diversity within the same plant species (Hauri et al, 2021;Weber et al, 2020;Grettenberger and Tooker, 2015).…”

“…Previous studies have shown that woodland strawberry exhibits genetic variation in its resistance to chewing herbivores (Weber et al, 2020). Both resistance and plant diversity per se help protect woodland strawberry from chewing herbivores (Koski et al, 2021). Although aphids are among the most destructive herbivores, causing serious production losses to both wild and cultivated strawberry (Valério et al, 2007), it remains unknown how herbivore resistance might affect aphids and their natural enemies -especially in combination with plant diversity.…”