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Quantitative trait loci (QTLs)
for resistance to gray leaf spot and common rust diseases of
maize
Jedidah Danson*, Martin Lagat, Michael Kimani
and Alex Kuria
Kenya
Agricultural Research Institute, Biotechnology Centre, P.O.
Box 14733, Nairobi 00800.
*Corresponding author. E-mail:
j.danson@cgiar.org.
Accepted
2 June, 2008 |
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Gray leaf spot and common rust diseases can greatly reduce
grain yield of maize in susceptible genotypes by between 10
and 70% on average. Control of these diseases through
conventional measures has been quite ineffective and
difficult to sustain. The most feasible way to control them
is by breeding and deploying resistant maize genotypes. This
study was carried out to evaluate germplasm for QTLs
associated with resistance to GLS and common rust diseases
by use of microsatellite markers and artificial inoculation
with the two pathogens. A total of 41 genotypes comprising
23 recombinant inbred lines, 14 parental inbred lines and 4
hybrid checks were screened using 28 SSR markers and disease
pressure by artificial inoculation (Tables 1 and 2). Out of
the 14 parental inbred lines, only 4 were found to carry the
QTL associating positively for the two diseases, and 10 out
of the 23 recombinant inbred lines with possible lineage
from any of the 14 parents, were positively associated with
the traits and seven of the markers used (Table 3). GLS QTLs
were significant for two markers; bnlg1258 with a LOD score
of 16.0 and umc2019 with a LOD score of 17.9 from regions
2.06 and 2.08 of chromosome 2, respectively. Significant
QTLs for common rust resistance were identified in three
regions of chromosome 10, corresponding to markers phi054
with a LOD score of 14.0 at bin 10.00, umc1319 with a LOD
score of 4.0 at bin 10.02 and bnlg1451 with a LOD score of
14.3 at bin 10.03. The effects of these QTLs were different
from genotype to genotype. The disease severity scores
(scale of 1-5) of artificial inoculation ranged from 1.5 to
2.5 for gray leaf spot with a mean of 1.88 and a range of
1.5 to 3.0 with a mean of 1.74 for common rust. All the
inbred lines scored better for the two diseases than the
four hybrid checks which scored 3.5. The most resistant
genotypes showed a score of 1.5 for gray leaf spot and
common rust. All parents showed a score of less than 2.5 for
GLS and common rust. Parental genotypes MAL40, MAL9, MAL13,
MAL41, MAL11, MAL19, MAL23-2,
MAL24, and MAL19-1, carried QTLs associated with resistance
to grey leaf spot and common rust and thus were identified
as sources of resistance conferred to the inbred lines.
The selected lines are being used to make single hybrids,
double crosses, three way hybrids and synthetics resistant
to diseases. The marker data was also used to analyze the
diversity of the genotypes studied, with relevance to
immune/resistant, tolerant or susceptible to the two
diseases. Using the GLS genotypic data, 13 genotypes
clustered into 11 groups, and using the common rust data,
the 13 genotypes clustered into 12 clusters. This indicates
that almost each of these genotypes was grouped in a cluster
that contained lines that did not have positive association
of marker and trait data. These results indicated that the
putative QTLs for GLS are associated with the 13 genotypes
and two markers in chromosome 2 (bnlg1258 and umc2019),
whereas those of common rust are associated with the 13
genotypes and three markers on chromosome 10 (phi054,
umc1319, and bnlg1451).
Key
word:
GLS, CR, QTLs, resistance, SSR, maize. |
