Insect mediated outcrossing and geneflow in cowpea (Vigna unguiculata (L.) Walp): Implication for seed production and provision of containment structures for genetically transformed cowpea

  • JAN Asiwe
Keywords: Cowpea varieties, geneflow, insect pollinators, out-crossing.

Abstract

Insect mediated out-crossing poses a lot of problems in plant breeding and seed production by creating unwanted genotypes or off-types in the field including mixtures in seed lots. Removal of off-types in the
field or seed lots increases costs of production. Information on level of out-crossing in cowpea and its insect pollinators as well as associated pollen movement would be useful in developing strategies to reduce outcrossing related problems. The objectives of this paper were to identify insect pollinators of cowpea, determine the level of outcrossing in the crop, and its implications in the deployment of genetically transformed cowpeas. Two experiments were conducted in Nigeria (IITA Ibadan and Mokwa) and Benin Republic (Cotonou) to assess geneflow frequency in cowpea under different planting arrangements. The first experiment was to quantify level of insect mediated out-crossing when three cowpea varieties (IT95K-1491, Sanzi, and IT86D-719) were respectively planted in alternate rows (one
metre apart) with IT95K-1093-5. The second was to assess the level of insect mediated outcrossing when IT95K-1491, a breeding line with morphological marker (anthocyanin pigment), was planted in 3 -
4 concentric inner rows of 1 m apart while IT95K-1093-5 was planted in outer concentric rows up to 16 m from the epicenter. Incidence of insects visiting the plots was taken during the flowering stage of the
crop. During harvesting, pods of IT95K-1093-5 were harvested from every plant within 3 - 4 m length along north, south, west and east axes of each concentric circle. In the case of alternate row planting,
pods from single plants were harvested from rows of IT95K-1093-5 of each pair. Seeds derived from these plants (IT95K-1093-5) were planted in the field in order to assess the level of outcrossing that
resulted from the movement of pollens from IT95K-1491, Sanzi, and IT86D-719 onto IT95K-1093-5 in the case of alternate row planting and IT95K-1491 onto IT95K-1093-5 for the concentric planting. Percentage of hybrids bearing the morphological trait of the marker parent was determined. Results obtained showed that level of out crossing was higher (0.5 to 0.85%) when cowpea was planted in alternate rows than in concentric rows (0.01 to 0.13%). Outcrossing was found to have occurred in a random fashion beyond 13 m. Among the insects observed, only honey and bumble bees were found with cowpea pollen dusts on their legs and abdomens, and were responsible for the observed level of outcrossing.
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eISSN: 1684-5315