MOLECULAR TAGGING OF GENE FOR BPH RESISTANCE IN RICE (Oryza sativa L.) cv. BM71
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Date
2011
Authors
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ACHARYA N.G. RANGA AGRICULTURAL UNIVERSITY
Abstract
Rice is cultivated in more than 100 countries around the globe and its significance as
food crop is ever increasing as the world population continues to explode. Insects are a
serious threat to cereal crops and cause significant damage to crop production annually.
Rice crop is host to a large number of insects that feed on rice. Of the six kinds of
planthoppers, brown planthopper (BPH; Nilaparvata lugens Stål) (Homoptera:
Delphacidae) is the most damaging insect pest of rice in Asia. Earlier studies documented
tremendous genetic variation for BPH resistance existing in rice germplasm. Knowledge on
the molecular markers linked to genomic regions associated with BPH resistance to enable
marker assisted selection in breeding programmes.
In this study, an attempt was made to trace BPH resistance loci from BM 71, a
derivative of MTU4569/ARC6650//Bunnan///IR64, a medium duration, high yielding
culture resistant to BPH using simple sequence repeat (SSR) markers. MTU 3626, a semi
dwarf, medium duration, high tillering, coarse grain, high yielding variety susceptible for
BPH developed from the cross IR8/MTU3 was crossed to BM71 to produce F2:3
population. A total of 170 F2:3 population were used for screening against BPH using
Standard Seed Box method. The parents, BM 71 showed moderate resistance (damage
rating of 3.3) to BPH when MTU 3626 showed complete susceptibility (damage rating of
9). The damage rating of F2:3 population ranged from 2.69 to 9.0 with an average of 6.36.
Genetics of BPH resistance in the cross MTU 3626/ BM 71 did not show Mendelian
segregation. Quantitative and transgressive nature of BPH resistance was observed in the
F2:3 segregating population.
Parental polymorphism survey was conducted between the parents MTU 3626 and
BM 71. A total 235 markers were tested, of which, 46 (19.57%) of the markers showed
polymorphism. Bulked segregant analysis using phenotypic extremes was carried out by
using 46 polymorphic SSR primer pairs in bulks (resistant and susceptible) made based on
F2:3 phenotypic extremes. Out of 46 polymorphic primer pairs, 2 primer pairs i.e., RM
19660 (chromosome 6) and RM 20037 (chromosome 6) were polymorphic in bulks. Single
marker analysis was done by using genotypic and phenotypic data of entire population and
found that the markers RM 19660 and RM 20037 were significantly associated with BPH
resistance at <0.01 probability and contributing 40.1 % and 25.7% of total phenotypic
variation. Linkage analysis of two polymorphic marker data showed significant linkage
between RM19660 and RM20037 at <0.001 probability and the distance between markers
was 28.5 cM. In simple interval mapping, the threshold LOD for BPH resistance at 0.05
and 0.01 levels are 8.28 and 11.78 respectively. Simple interval mapping has identified a
major QTL between RM 19660 and RM 20037 with a LOD value of 54.39 at a peak
position 15 cM distance. The QTL is placed at 12 cM away from left side of RM19660 and
11cM away from right side of RM20037. This QTL has explained 32% of total phenotypic
variation with additive and dominance variance of 1.33 and 1.75 respectively.
Overall results of the study suggested the possibility of a genetic locus on
chromosome 6 significantly associated with BPH resistance in the mapping population of
the cross MTU 3626/ BM 71. Fine mapping of the genomic region influencing BPH
resistance in the present study may be taken up by developing RILs for identification of
closely linked markers which can be used in Marker Assisted Breeding programmes
Description
Keywords
rice, genes, chromosomes, polymorphism, planting, genetics, dna, phenotypes, genomes, breeds (animals), Oryza sativa L.),