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Gene flow
between cultivated and wild cowpea in Kenya
R.S. Pasquet,
A. Ochieng & K. Thoen
The wild progenitor of cultivated cowpea (Vigna
unguiculata ssp. unguiculata var. spontanea) is encountered in all
humid lowland ecologies of Kenya, including the areas surrounding Lake
Victoria, between 1000 and 1500 m in Central Kenya, and in the coastal
plains. In the coastal plains, a second wild cowpea subspecies (V.
unguiculata ssp. pubescens) is also encountered but hybridization
between this subspecies and cultivated cowpea is not common. In all
these areas, wild cowpea shows a weedy behavior and is much more present
in disturbed areas, often in the vicinity of cultivated cowpea.
Genetic structure of representative populations as well as
outcrossing rates (in natural conditions) are assessed using isozyme
markers. Results suggest that gene flow between populations is low.
Within populations, isozyme polymorphism is lower than expected (since
some populations have an outcrossing breeding system) and may be too low
to accurately really assess gene flow events.
Floral biology data, i.e. floral scent, nectar secretion, number
of pollen grains and ovules, anthesis time, stigma receptivity, the
anthers and stigma relative position of, and seed set are presented.
Breeding systems range from total outcross (few wild populations) to
inbred (in cultivated plants). Pollinators
are identified as carpenter bees and several Megachiles. They collect
nectar and are normally visit each flower twice (at sunrise and once
after the nectar is refilled). They do not exhibit flower color
preferences or species prefences (when V.
reticulata flowers are close to V.
unguiculata flowers). They fly short distances while foraging and up
to now, attempts to prove gene flow between plants beyond 50 m have
failed. Fitness of hybrids
is assessed. F1 hybrids are obiously more fit than their parents,
especially when one mother plant is a cultivated plants. They produce
many seeds. However, these seeds are not dormant which may explain the
low amount of hybrid plants found in natural populations.
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