QTL DISCOVERY AND MAPPING HOST-PLANT RESISTANCE FOR DOWNY MILDEW PATHOGEN IN PEARL MILLET (Pennisetum glaucum [L.] R. Br.)
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Date
2014
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ACHARYA N. G. RANGA AGRICULTURAL UNIVERSITY. RAJENDRANAGAR, HYDERABAD
Abstract
The present study was undertaken at ICRISAT-Patancheru to construct a skeleton
genetic linkage map for a pearl millet mapping population of 295 RILs of cross, 81B-P13
and AIMP 92901-deriv-P03, to identify and map QTLs controlling downy mildew
resistance (DMR) for new virulent downy mildew isolates from Gujarat, Rajasthan and
Haryana.
Pearl millet downy mildew, caused by Sclerospora graminicola, is the most
devastating disease of pearl millet causing huge grain and straw production losses in India.
The allogamous and highly variable natures of both the host and pathogen are great
hindrances to breeding for host plant resistance to this disease. Effective and economic
control of this disease can be achieved by growing disease resistant varieties and hybrids.
In order to develop disease resistant cultivars, it is important to have DMR QTLs mapped.
The available 20 pairs of mapping population parental lines were screened along
with control entries 7042(S), 843B, 843-22B, ICMP 451 and IP 18292 against three isolates
of DM pathogen population from Gujarat (Sg445), Haryana (Sg519) and Rajasthan
(Sg526). 81B-P13 × AIMP 92901-S1-15-1-2-B-P03 RIL mapping population was selected
for mapping of DMR QTLs on basis of high contrast for downy mildew resistance and
susceptibility.
Mapping population of 295 RILs were used to isolate nuclear DNA that was
genotyped for 80 polymorphic SSR, EST-SSR and STS marker loci. About 34% of
polymorphic marker loci showed Mendelian segregation ratio of 1:1, while 66% of
polymorphic marker loci showed segregation distortion.
A skeleton linkage map of seven linkage groups with a total map length of 536.8cM
(Haldane units) was constructed using data from 39 marker loci for 295 RILs using
MapMaker/Exp version 3.0b at LOD threshold value of 3.0 and map was drawn using Map
Chart 2.2. Among all the linkage groups of the present study, linkage group1 has the
highest map length (146.6cM) followed by linkage group 2 (98.3cM). The linkage group 3
(6.6cM) has been recorded as the shortest among all seven linkage pearl millet groups in
this study.
For QTL mapping, Composite interval mapping as implemented in QTL
Cartographer version 2.5 at threshold likelihood ratio of 3.0 for declaration of QTL
significance was employed. A total of four different major isolate specific resistant QTLs
were identified from three screens of the F7 RIL mapping population against pathogen
populations from India. Two QTLs were identified on Linkage Group1 (LG1) against
Sg445 and Sg526, one QTL on LG3 against Sg445 and another QTL on LG4 against
Sg519. The inheritance of these QTLs showed AIMP 92901-deriv-P03 providing the
resistance alleles. The highest LOD score for the QTL identified on LG4 was 41.0 with
largest amount of observed phenotypic variation was contributed by the QTL on LG4 was
75.59.
At least one DMR QTL was detected and mapped for each of the three DM isolates.
After validation, marker-assisted selection (MAS) can now be used for improving DMR of
elite pearl millet hybrid parental lines using polymorphic flanking markers from donor
parent AIMP 92901-deriv-P03.
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Keywords
QTL, DISCOVERY, MAPPING, HOST-PLANT, RESISTANCE, DOWNY, MILDEW, PATHOGEN, PEARL MILLET