Genetic study of cowpea (Vigna unguiculata (L.) Walp) resistance to Striga gesnerioides (Willd.) vatke in Burkina Faso.
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Date
2010
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Abstract
In Burkina Faso, the existence of different races of Striga gesnerioides (Willd.) Vatke, with
apparent variable aggressiveness on cowpea (Vigna unguiculata (L.) Walp) renders the
breeding task very complex. Therefore, a number of studies was carried out from 2006 to
2009 in field, pot and ‘’in-vitro’’ to identify new sources of resistance to three prevailing
Striga races, SR 1, SR 5 and a newly occurring Striga race named SR Kp and to
understand the genetic pattern of the underlying resistance of cowpea germplasm to Striga
races found in Burkina Faso.
To achieve these objectives, the following investigations were initiated: (i) a participatory
rural appraisal (PRA), a participatory variety selection (PVS) and grain quality survey were
implemented to identify cowpea breeding priorities for Burkina Faso Striga hot-spots; (ii) the
identification of sources of resistance in Burkina Faso germplasm, using three prevailing
Striga races of S. gesnerioides as sources of inoculum; (iii) the identification of the
mechanisms of resistance underlying the resistance to Striga in such genotypes; (iv) a
study of combining abilities of selected parents through a diallel cross; (v) a study of the
segregation patterns in crosses involving resistant and susceptible sources and a study of
the allelic relationships between different resistance sources.
The participatory studies conducted in 2007 and 2008 over three districts in Striga hotspots;
there was no effective control method against Striga at farmers’ level. These
investigations highlighted the importance of cowpea across all sites. Rain decline over time,
low input use coupled with a poor extension system were the major constraints mentioned
by farmers. Differential reactions of genotype KVx61-1 for Striga resistance suggested that
different Striga races were prevailing in different areas. Farmers’ preferred traits in cowpea
genotypes were oriented towards grain quality such as big sized grain, white seed colour
and rough texture of cowpea grain, except in Northern-Burkina Faso, where farmers
preferred brown-coloured grain for food. Cowpea was also seen as an income generating
crop.
An evaluation of 108 genotypes was done in 2007 in the field (rainy season) and in pots
(off-season) for Striga resistance assessments. The screening trials enabled the
identification of sources of resistance to S. gesnerioides. Genotypes KVx771-10, IT93K-
693-2, KVx775-33-2, Melakh and IT81D-994 are potential sources of resistance to all three
Striga races with acceptable yield. Landraces were susceptible and late-maturing whilst
most wild species were resistant but with unwanted shattering traits.
A combining ability study for Striga resistance parameters conducted in pots and a
resistance mechanism study conducted ‘’in-vitro’’ were performed using F1 populations from
a 10 x 10 diallel cross. The general combining ability (GCA) effects were significant for the
resistance parameters Striga emergence date (DSE), Striga height above soil (SH), cowpea
grain weight (CGW), hundred grain weight (HGW) for all Striga races involved and Striga
vigour (SVIG) for SR 5 and SR Kp. The pot-screening showed that, regardless of the SR
used as inoculum, the additive genes were important in conferring Striga resistance for
parameters DSE, SH, CGW and HGW. The selection of parents could therefore result in
breeding advance. Complete dominance, partial, over-dominance and non-allelic
interactions (epistasis or failure of some assumptions) were present for some parameters.
The ‘’in-vitro’’ screening showed that additive genes were important, with high narrow sense
heritability values for the resistance mechanisms Striga seed germination frequency (GR)
for SR 1 and SR Kp, the frequency of Striga radicle necrosis before the penetration in
cowpea rootlet (NBP) for SR 5, the frequency of Striga radicle necrosis after the penetration
in cowpea rootlet (NAP) for SR 1 and SR Kp and the susceptibility ‘’in-vitro’’ (SIV) for SR 5
and SR Kp. The selection of parents can be useful in accumulating the genes for Striga
resistance mechanisms in progenies.
The F2 populations derived from crosses between Striga-resistant x susceptible genotypes
were evaluated in Striga infested benches in 2008 and 2009. The segregation patterns
suggest that single dominant genes govern Striga resistance. The test for allelism showed
that two non-allelic genes were responsible for the resistance to S. gesnerioides in cowpea.
A new Striga resistance gene seems to be involved in genotype KVx771-10 resistance to S.
gesnerioides, which confers resistance to all studied Striga races. Gene 994-Rsg in
genotype IT81D-994 which confers Striga resistance to SR 1 and gene Rsg 3 also
conferring Striga resistance to SR 1 segregated differently for the resistance to SR 5
suggesting that they were different but both confer resistance to SR 5.
Description
Keywords
Cowpea--Disease and pest resistance--Genetic aspects., Cowpea--Breeding--Burkina Faso., Cowpea--Burkina Faso--Genetics., Striga., Cowpea--Varieties--Burkina Faso., Farmers--Burkina Faso., Theses--Plant breeding., Cowpea--Diseases and pests--Burkina Faso.