Abstract
Castor bean (Ricinus communis L.) is cultivated mainly for biodiesel production because of its oil-rich seeds; it is assumed to be an anemophylous species. But pollination deficit can lead to low productivity often attributed to other reasons. In this paper, we investigated pollination requirements, pollination mechanism, occurrence of pollination deficit, and the role of biotic pollinators in a large commercial plantation of castor bean. Our results show that R. communis bears a mixed breeding system favoring selfing by geitonogamy, although the wind promotes mostly outcrossing. We also found that the honey bee (Apis mellifera L.) foraging on castor bean can both transfer pollen from male to female flowers within the same raceme and boost the release of airborne pollen by male flowers. Both situations increase geitonogamy rates, raising significantly fruit set and seed yield. This is the first report of an animal foraging activity increasing seed yield in an anemophilous and geitonogamous crop and elucidates the role of biotic pollinators in castor bean reproduction.
Highlights
The castor bean (Ricinus communis L.) is an oil crop originated from Africa and cultivated world wide (FAOSTAT; http://faostat.fao.org/site/339/)
Due to the enormous size of the areas cultivated with castor bean and consequent distance to natural vegetation (Fig. 2a), wild floral visitors were almost nonexistent and the honey bee foraging behavior was only possible after introducing eight colonies nesting in Langstroth hives in the center of one of the 43.75 ha area within field U
All castor bean nectar was produced by extrafloral nectaries found at junctions of the plant, including on the base of each flower pedicel (Fig. 2c) making racemes the parts of the plant with greater concentration of extrafloral nectaries and the most visited by nectar collectors
Summary
The castor bean (Ricinus communis L.) is an oil crop originated from Africa and cultivated world wide (FAOSTAT; http://faostat.fao.org/site/339/). Since ancient times it has been exploited for its oil which was used as ingredient to cosmetics, shampoo, soap, hand lotion, laxative, fuel for lamps and as a high speed lubricant (Capasso et al 1994, Copley et al 2005, Morris et al 2011). Castor bean is cultivated mainly for biodiesel production because. In 2009, the average castor bean yield varied considerably from 1,307.1 and 904.7 kg seeds/hectare (ha = 100 acres) in India and China, respectively, to only 567.7 kg seeds/ha in Brazil (FAOSTAT; http:// faostat.fao.org/site/567/). Growers try to compensate low productivity enlarging the planted area at the expenses of native vegetation (Rizzardo et al 2008)
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