Abstract
We investigated levels of pollinator dependency and pollinator visitation rates to flowers of six vegetable crops: brinjal (aubergine), tomato, chilli pepper (Solanaceae), okra (Malvaceae), bitter and snake gourds (Cucurbitaceae) in six small family farms in the Coimbatore region of southern India. We tested the null hypothesis that fruit set in these crops would be independent of pollinators. We assessed fruit set through self and cross pollination by pollen augmentation, by pollinator exclusion and open pollination. We evaluated pollen limitation by comparing percentage fruit set by hand outcrossed pollen with open pollination; pollinator dependency by differences in percentage fruit set by open pollination and autogamous pollination; and visitation rates to flowers by pollinating insects. Tomato, chilli and okra produced self-compatible hermaphrodite flowers, with higher levels of autogamous fruit set (32-76%) and significantly lower levels of pollinator dependency (0-37%), whereas andro-monoecious brinjal and monoecious gourds had significantly lower levels of fruit set through autogamy, and higher levels of pollinator dependency. Pollen limitation was not evident in any crop. Diverse pollinating insects visited the flowers, and the frequency of visits by different pollinator taxa differed with crop type. Native vegetation and uncultivated land may enhance pollinator diversity in small farms.
Highlights
In many cases the fruit set through cross pollination treatment (CP) was lower than that resulting from open pollination (OP), which could be due to damage to floral parts while emasculation, or poor quality pollen
Pollinator dependency (PD) ranged from 8-76% across all crop varieties except tomato (Tab. 2)
Our study shows that levels of pollinator dependency ranged from 0% in tomato to 76% in bitter gourd, and pollinators are required for fruit set in five of the six crops
Summary
Pollinators are critical for the reproduction of many plants, and about 94% of plant species in tropical communities and a third of global food crops are likely to rely on animal pollination (McGregor 1976; Klein et al 2007; Ollerton et al 2011). Aizen et al (2009) suggested that in the absence of pollinators, reduction in crop production would range from 3-8% (Allen-Wardell et al 1998; Kearns et al 1998; Klein et al 2007; Garibaldi et al 2013). Aizen et al (2009) suggested that in the absence of pollinators, reduction in crop production would range from 3-8% (Allen-Wardell et al 1998; Kearns et al 1998; Klein et al 2007; Garibaldi et al 2013). Tropical agriculture could be susceptible to pollinator declines since the cultivation of pollinator dependent crops, and the use of pesticides has increased (Roubik 1995; Aizen et al 2009). As proximity to forests has been shown to increase pollinator activity and enhance crop production (De Marco & Coelho 2004; Ricketts et al 2004, 2008; Blanche et al 2006), tropical deforestation could further imperil pollination services (Bradshaw et al 2009). The Indian green revolution which started in the 1960’s with the introduction of high yielding varieties and the intensive use of organophosphates, carbamates, synthetic pyrethroids
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