Re‐evaluating strategies for pollinator‐dependent crops: How useful is parthenocarpy?

Abstract

Summary Whilst most studies reviewing the reliance of global agriculture on insect pollination advocate increasing the ‘supply’ of pollinators (wild or managed) to improve crop yields, there has been little focus on altering a crop's ‘demand’ for pollinators.Parthenocarpy (fruit set in the absence of fertilization) is a trait which can increase fruit quantity and quality from pollinator‐dependent crops by removing the need for pollination.Here we present a meta‐analysis of studies examining the extent and effectiveness of parthenocarpy‐promoting techniques (genetic modification, hormone application and selective breeding) currently being used commercially, or experimentally, on pollinator‐dependent crops in different test environments (no pollination, hand pollination, open pollination).All techniques significantly increased fruit quantity and quality in 18 pollinator‐dependent crop species (not including seed and nut crops as parthenocarpy causes seedlessness). The degree to which plants experienced pollen limitation in the different test environments could not be ascertained, so the absolute effect of parthenocarpy relative to optimal pollination could not be determined. Synthesis and applications. Parthenocarpy has the potential to lower a crop's demand for pollinators, whilst extending current geographic and climatic ranges of production. Thus, growers may wish to use parthenocarpic crop plants, in combination with other environmentally considerate practices, to improve food security and their economic prospects.

Yield benefits of additional pollination to faba bean vary with cultivar, scale, yield parameter and experimental method

“…This value is based upon estimates of the "pollinator dependence" of each crop; the proportion of harvestable yield that depends on animal mediated pollination, or how much yield is lost in absence of such pollination.Recent studies have begun to show that the pollinator dependence of a crop is not fixed and that it interacts with other biological factors (soil quality and predation by pests 4-6 ) or agronomic inputs (fertilizer, agrochemicals and water 7-11 ), see review 12 .Pollinator dependence can also vary with crop cultivar, for example in apples 13 and oilseed rape 14 . Understanding pollinator dependence on a per-cultivar basis could enable crop producers to secure production as pollination services become less predictable 15,16 following shifts in pollinator populations through time 17,18 . In the short term, producers in landscapes with low levels of semi-natural habitat and pollination service capacity 19 may benefit from use of low-dependent cultivars, though this needs to be considered alongside other agronomic attributes (e.g.…”

“…Pollinator dependence can also vary with crop cultivar, for example in apples 13 and oilseed rape 14 . Understanding pollinator dependence on a per-cultivar basis could enable crop producers to secure production as pollination services become less predictable 15,16 following shifts in pollinator populations through time 17,18 . In the short term, producers in landscapes with low levels of semi-natural habitat and pollination service capacity 19 may benefit from use of low-dependent cultivars, though this needs to be considered alongside other agronomic attributes (e.g.…”

Courgette Production: Pollination Demand, Supply, and Value

“…As Cornwall already benefits from biodiverse hedgerows and generally smaller field sizes, availability of floral resources may be strongly influencing the high pollination rates observed in this study and is a clear incentive for growers in this region to maintain and protect these habitats to ensure high and stable pollination services in the future. Growers may also benefit from using crop varieties which have been selectively bred to be fully parthenocarpic (currently not done by commercial growers of courgette), especially in combination with pollinator-supportive practices (Knapp et al 2016). …”

“…Realistic estimates of the amount of insect pollination required for optimum fruit set need to account for not only the variability in pollination deficit that might result from variable pollinator densities and environmental conditions, but also the variability in pollinator dependence between varieties of single crop species, for which there is currently little good evidence (Melathopoulos et al 2015, Knapp et al 2016, although see Garratt et al 2014). In the wider context, discussion and strategies for improving horticultural crop production need to incorporate costs and benefits associated with different methods of maximizing pollination, while remembering that factors other than pollination also contribute to fruit set.…”

“…Excluding pollinators from some cucurbits has shown that fruit set is unable to occur (Hoehn et al 2008) and that increased pollen loads can make fruit grow faster and larger (Stephenson et al 1988, Artz and. However, the dependence of a crop species on pollinators is likely to vary between varieties (Knapp et al 2016). For example, 22 out of the 33 summer squash varieties have been shown to set fruit without pollination (Robinson and Reiners 1999).…”