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Insect mediated
outcrossing and geneflow in cowpea (Vigna unguiculata
(L.) Walp): Implication for seed production and provision of
containment structures for genetically transformed cowpea
Asiwe, J. A. N.
Agricultural Research Council (ARC), Grain Crops Institute,
Private Bag X1251, Potchefstroom 2520, South Africa. E-mail:
AsiweJ@arc.agric.za.
Fax: +27 18 294 7146.
Accepted
28 November, 2008 |
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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.
Key
words:
Cowpea varieties, geneflow, insect pollinators,
out-crossing. |
