GENETIC ANALYSIS OF PLANT MORPHOLOGY IN
BAMBARA GROUNDNUT [Vigna subterranea (L.) Verdc.]
Abstract
Bambara groundnut (Vigna subterranea (L.) Verdc.) is an important underutilised
legume crop, grown mainly by female subsistence farmers in Africa under traditional
low input agricultural systems. Bambara groundnut is known as being of high
nutritional value, as an atmospheric nitrogen fixer and to possess high levels of
drought, pest and disease tolerance. Bambara groundnut is a predominantly selfpollinated crop and is grown as locally adapted landraces. These are expected to exist as
non-identical inbred lines and are generally low yielding. Strategies involving genetic
analysis of this species could provide important data for breeding programmes that
could enhance food security in Africa.
A set of 124 SSR primers designed from different library sources were tested to
screen a ‘narrow’ genetic cross (F3) and a ‘wide’ genetic cross (F2) . The former is a
cross between domesticated landraces (DipC and Tiga necaru) while the latter is a
cross between a domesticated landrace and a wild ancestor (DipC and VSSP11).
Residual heterozygosity in the F3 ‘narrow’ cross was confirmed to be around 25%
based on 33 polymorphic SSR primers, consistent with an F3 population. A ‘narrow’
cross linkage map was constructed for the first time in bambara groundnut using 269
polymorphic markers (236 DArT and 33 SSR). The map consisted of 238 markers in
21 linkage groups of two or more linked markers, totalling 608.1cM and covering a
predicted 54% of the bambara groundnut genome, although the high marker-marker
linkage (at 89%) suggests a more comprehensive coverage. QTL analysis was carried
out for 73 bulked lines of an F3 population and plants were evaluated for traits in a
controlled glasshouse suite and a field trial in Indonesia. Data from single plant
analysis of the F2 generation of this cross grown in a controlled environment
glasshouse was also used. Most of the QTLs detected were clustered on linkage
groups 1, 4 and 12. Major QTLs for internode length and biomass dry weight were
detected on LG4 and LG1, respectively, for the FutureCrop glasshouse and field
datasets. The highest LOD score of 9.7 was detected for peduncle length and was
located within the confidence interval for a QTL for internode length locus. Marker
locus bgPabg-596774 was detected to be associated with QTL for six traits; node
no./plant, pod no/plant, pod weight, seed no./plant, seed yield and biomass dry
weight, on LG1 within one LOD score of confidential interval, potentially suggesting
pleiotropic effects of a more limited number (or even one) gene(s).
One hundred and fifty-nine additional markers (136 DArT and 23 SSR) were used to
improve the existing partial ‘wide’ map (141 AFLP, 1 SSR) constructed in an F2
population of 98 plants. A total of 194 markers were assigned to 20 linkage groups
spanning a total of 901 cM. The linkage map derived from the ‘wide’ cross (DipC x
VSSP11) had an expected genome coverage of 79.6%. An attempt to combine both
maps through 32 common markers allowed a common QTL for days to emergence to
be detected in both populations in close association with the common DArT markers
601384 and 601748.
The main segregating traits were found to be plant spread, internode length, growth
habit, peduncle length, pod weight, seed yield and biomass dry weight. Detecting the
same QTL positions for a number of traits, suggested that common underlying genes
might be responsible. The QTL-DNA marker associations developed in this study
could be used practically for MAS in a future breeding program of this crop.