MARKER ASSISTED SELECTION FOR BACTERIAL LEAF BLIGHT RESISTANCE IN RICE (Oryza sativa L.)
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Date
2019
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Acharya N G Ranga Agricultural University, Guntur
Abstract
Nellore Mahsuri (NLR34449) is a local popular rice variety, and is mostly adopted by many of the farmers due to its fine grain nature, short duration, non-lodging, saline resistance with high yielding nature and suitability for cultivation in any season. This variety is also resistant to one of the major diseases of rice, leaf blast but susceptible to bacterial leaf blight (BLB), another most devastating disease in rice growing areas. To combat the problem, development of varieties carrying resistant genes has been considered to be the most effective way to control the BLB disease and is economical and environmentally safe option for management of BLB.
In the present investigation an attempt was made to improve NLR34449 for BLB resistance by introgressing three major resistant genes viz. Xa21, xa13 and xa5 from RPBio226 (Improved Samba Mashuri) using marker assisted selection. When phenotypic screening of NLR34449 and RPBio226 was done with artificial inoculation of pathogen, it revealed that NLR34449 was found to be susceptible as it showed lesion length of 5.0 -7.5 cm at 7 days after inoculation when compared to RPBio226, that showed hypersensitive reaction to the pathogen. Similarly, the genotyping of these two varieties using three gene specific markers namely pTA248, xa13prom, xa5FS, linked to the BLB resistance genes viz., Xa21, xa13 and xa5, respectively revealed that the NLR34449 is lacking these broad spectrum genes.
The two parents were crossed to produce F1. True F1s were confirmed using gene specific markers xa13prom (xa13), pTA248 (Xa21), xa5FS (xa5). BLB gene positive F1s were allowed to undergo self pollination to produce F2 seed. Initially 90 F2 plants were screened phenotypically by using artificial clip inoculation method. A total of 22 plants that fell in the resistant and moderately resistant classes with lesion length of 0.6 – 4.3cm were selected and subjected for genotypic screening by employing three gene specific markers namely pTA248, xa13prom, xa5FS, linked to the BLB resistant genes viz., Xa21, xa13 and xa5, respectively. Out of 22 plants, 3 were found to be positive for xa13 and Xa21 and 4 plants were positive for xa5 gene, whereas, two plants each were double positive for the gene combinations Xa21 + xa13, xa13 + xa5 and for Xa21 + xa5. Only, one F2 plant possessed all three genes in homozygous condition i.e. of RPBio226 alleles. the plants that consisting of the combination of xa13 and Xa21, the broad spectrum genes were artificially re-inoculated with the increased dose of inoculum (10-8 cfu/ml) to confirm their resistance level to the pathogen. At higher concentration also the gene pyramided plants showed very less disease reaction i.e. ranged from hypersensitivity reaction to 2.7cm. Thus, they were confirmed as BLB resistant plants.
In conclusion, in the present investigation NLR34449 variety, which is high yielding, fine grain, and susceptible to BLB disease has been pyramided with three BLB genes from RPBio226. Hence, the potency of early generation selection method can be once again highlighted from the study in pyramiding of two or more genes at F2 generation itself which might not be possible with conventional approach alone. Hence, identification of tightly linked markers for the desirable traits needs to be hastened up for the varietal development wherein it is achievable at faster pace with the knowledge available in the sequence based databases.
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D5867
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