STUDY CASE 05
Economic value of cashew (Anacardium occidentale L.) to Brazil and its need for pollination
Breno Magalhães Freitas
Cashew (Anacardium occidentale L.) is a andromonoecious tree native to NE Brazil. It is of considerable economic importance to the region for its nut, oil and cashew apple production. An estimate economic value of cashew to Brazil per year shows the following figures:
However, crop yields are disappointingly low from commercial orchards and studies suggest that inadequate pollination could be the major cause to cashew low productivity. Cashew's flower form and presentation suggest that it is pollinated by insects, especially bees. Although wind and numerous insects that visit cashew flowers, namely wasps, butterflies and ants, have been cited as pollinators they fail to set fruits in most cases, showing clearly that flower visitor and pollinator are not synonymous. Only bees visit and set cashew flowers regularly in NE Brazil. Two bee species are particularly efficient in pollinating cashew flowers: the solitary indigenous bee Centris tarsata and the exotic honey bee (Apis mellifera).
But there are two sides to the shortfall of adequate pollination of commercially grown cashew in NE Brazil. On the one side, there are few or no visits to orchard-grown cashew flowers. Apis mellifera does not readily visit cashew flowers even when brought into orchards in large numbers because of competing weeds in bloom. The other suitable pollinator, C. tarsata, is rare in commercial cashew orchards due to habitat disturbance and the lack of rearing techniques to breed them in large numbers. A second side to this shortfall is undoubtedly related to horticultural practices in which a partially self-sterile clonal strain is grown over large areas without thought being given to the need for compatible sources of pollen. This problem is exacerbated as more and more cultivated areas are being planted or replanted with dwarf clones. One obvious solution is to intercalate trees producing compatible pollen within main cropping strains. Hand-pollination experiments carried out in Australia and Brazil have identified types or strains of cashew, crossing among which produced higher yields. However, it will still be necessary to consider management of bees within commercial cashew orchards because they will be needed as the vectors of compatible pollen.
One can conclude that to improve cashew crop yields in NE Brazil, serious consideration needs to be given to both conservation and management of its recognised, efficacious pollinators (C. tarsata and possibly A. mellifera) and also the design of orchards with appropriate mixes of compatible cashew strains.
Edited from Freitas, B.M.; Paxton, R.J.; Holanda-Neto, J.P. (2002) Identifying pollinators among an array of flower visitors, and the case of inadequate cashew pollination in NE Brazil. In: Kevan, P. & Imperatriz-Fonseca, V. L. (2002) Pollinating bees: the conservation link between agriculture and nature. Ministry of Environment, Brasília, Brazil. p. 229 - 244.