MAPPING AND VALIDATION OF SSR MARKERS ASSOCIATED WITH FOLIAR-FUNGAL DISEASE RESISTANCE QTLs AND DEVELOPMENT OF RILs IN GROUNDNUT (Arachis hypogaea L.) 2928
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Date
2019-08
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JAU, JUNAGADH
Abstract
Groundnut (Arachis hypogaea L.) is an economically important oilseed crop which
is widely cultivated in semi-arid tropic regions of Asia, Africa and America. Two
devastating foliar-fungal diseases, viz., late leaf spot (LLS, Phaseoisariopsis
personata) and rust (Puccinia arachidis), which often occurs together causes heavy
losses along with adverse effects on the quality of kernel and fodder.
The objective of the present study was to identify and map the biotic stress
relevant candidate EST-SSR markers in the major QTL regions controlling resistance
genes for LLS and rust diseases and validate the identified linked markers in diverse
groundnut genotypes. The F2 mapping population consisting of 328 lines was
developed from diverse genotypes i.e. GJG 17 and GPBD 4. In the parental
polymorphism survey, 84 out of 1311 SSR markers were found polymorphic (which
includes 900 newly developed EST-SSR at ICAR-DGR and SSRs from the previous
reports). A total of 70 out of 84 markers were mapped on 14 linkage groups (LGs)
covering a total map distance of 797.55 cM with an average inter-marker distance of
11.39 cM.
In the bulk segregant analysis (BSA) four new EST-SSR markers namely
DGR329, DGR508, DGR800 and DGR2409 were identified as putatively linked to
LLS and rust resistance genomic region. A total of seven new EST-SSR markers,
including newly identified 4 markers with BSA, were successfully mapped in the LLS
and rust fine QTL region. Among them, DGR259 was found flanked to major LLS
QTL. One common QTL for LLS and rust was identified in the map interval of 1.41
cM (between SSR_GO340445 and FRS72) on linkage group (LG-A03) which
contributed 47.45% and 70.52% PVE variation, respectively. These two markers,
SSR_GO340445 and FRS72, were tightly linked to LLS and rust resistance. Another
major QTL for LLS was found on same linkage group (LG_A03), explained 29.06%
PVE flanked by the marker DGR259 and FRS59 close to LLS and rust common QTL.
The common QTL region identified for LLS and rust resistance carries one Resistance
ABSTRACTgene (R gene) and five resistance-related genes which shown to have role in inducing
a programmed cell death or hypersensitive response (HR) to combat pathogen attack.
A total of 7 new biotic stress relevant EST-SSR markers (DGR259, DGR312,
DGR329, DGR361, DGR508, DGR800 and DGR2409) were integrated in the major
QTL hotspot region, where one of it flanking the major LLS QTL region and six
markers showed tight association with major QTL region. Most EST-SSR markers
were from the genes involved in the disease resistance.
Initial validation carried out in selected genotypes showed that these markers were
able to distinguish resistant genotypes more clearly and efficiently. Further validation
of all the 24 SSR markers saturated in LLS and rust QTL region were validated in 177
diverse Indian genotypes. Of these, only 12 genotypes resistant to both LLS and rust
carries resistant alleles of markers flanking the LLS and rust QTLs and eight more
markers present in the surrounding region of these QTLs.
Moreover, the new identified EST-SSR markers were validated in the introgression
lines. All the markers were able to distinguish resistant introgression line from
susceptible recurrent parent and susceptible genotypes. These markers could be used
to introgress this fine QTL regions to improve LLS and rust resistance in the
groundnut breeding program more efficiently by minimizing the risk of linkage drag.
Furthermore, these markers will be of great help to the groundnut breeders for the
selection of resistant genotype from the segregating population, advanced breeding
lines and varieties even in the absence of a disease nursery or epiphytotics and will be
useful in MAS under crop improvement program