FINE MAPPING OF DOMINANT RICE GALL MIDGE RESISTANCE GENE, Gm4 USING MICROSATELLITE MARKERS
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Date
2004
Authors
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ACHARYA N.G. RANGA AGRICULTURAL UNIVERSITY RAJENDRANAGAR, HYDERABAD
Abstract
Rice gall midge is one of the serious insect pests of rice. Chemical control
of the pest is difficult and sometimes impossible and cultivation of varieties
possessing one or more genes conferring resistance against gall midge is the
economically feasible and ecologically viable strategy for its management. Many
varieties possessing single gene conferred resistance have become gall midge
susceptible due to emergence of virulent biotypes of the insect. Hence, many
researchers have suggested pyramiding 2-3 gall midge resistance genes in a single
genetic background for enhancing the durability of resistance. The dominant
resistance gene, Gm4 originally identified from Ptb10 is an ideal candidate for
deployment in gene pyramiding programmes. Gm4 was originally tagged with
RAPD based marker F43 and mapped to Chromosome 8 of rice using RFLP
markers by Nair et al. (1996) and Mohan et al. (1997) respectively. But none of
these markers have been validated in alternative populations nor used in any gall
midge resistance breeding programmes. The present study was designed to fine
map Gm4 with help of rice microsatellite markers specific for Chromosome 8 of
rice using the progeny tested F2 mapping population (consisting of 98 individuals)
derived from the cross TN1/Abhaya. About 15-18 F3 seedlings derived from each
F2 line were screened in a glasshouse using biotype 1 of gall midge to identify the
genotype of each F2 line. Resistant F3 seedlings were observed to show presence of
additional tiller and on dissection, they possessed necrotic brown discoloration in
the meristematic region. Susceptible F3 seedlings showed gall formation and
emergence of adult insect after 20th day of infestation. Twenty-six microsatellite
markers located on Chr. 8 were screened for molecular polymorphism between the
parental lines (TN1 and Abhaya) and six (RM547, RM25, RM337, RM152,
RM256, RM32) were observed to be parental polymorphic. These six markers
were analyzed in the F2 population for co-segregation with trait phenotype. Of the
six markers, only two, RM547 and RM25 were observed to exhibit clear cosegregation
with trait phenotype (resistance/susceptibility). Based on the cosegregation
analysis, the linkage distance between the two markers and Gm4 was
calculated to be 18.6 and 30.6 cM respectively with respect to RM547 and RM25.
The other markers did not show any clear co-segregation pattern. A linkage map of
Chr. 8 consisting of the five (excluding RM32) parental polymorphic microsatellite
markers has been constructed with a total linkage distance of about 133.1cM. The
two microsatellite markers RM547 and RM25 after further validation in a larger
sized mapping population can be used for marker-assisted selection of the gene.
Description
Keywords
FINE, MAPPING, DOMINANT, RICE, GALL, MIDGE, RESISTANCE, GENE, Gm4, MICROSATELLITE, MARKERS,