MARKER ASSISTED INTROGRESSION OF BACTERIAL LEAF BLIGHT RESISTANCE GENES INTO AN ELITE RICE VARIETY, NELLORE MASHURI
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Date
2018
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Acharya N.G. Ranga Agricultural University
Abstract
Nellore Mahsuri (NLR34449) is a popular rice variety, and mostly adopted by
many of the farmers by virtue of its fine grain appearance, short duration, non-lodging
and high yielding characters. This variety is resistant to leaf blast but susceptible to
bacterial leaf blight (BLB), the second most devastating disease in rice growing areas.
The development of resistant varieties has been the most effective and economical
strategy to control this disease.
In the present investigation, an attempt was made to improve the NLR34449
for BLB resistance by introgressing three major resistant genes i.e., xa13, Xa21and
xa5 from RPBio226 (improved samba Mahsuri) using marker-assisted backcross
breeding. Phenotype screening of Nellore Mahsuri (NLR34449) and RPBio226
revealed that NLR34449 is found to be susceptible as it showed more lesion length in
comparison to the RPBio226. Similarly, the genotyping of these two varieties using
three gene specific markers namely pTA248, xa13 prom, xa5FS, linked to the BLB
resistance genes viz., Xa21, xa13 and xa5, respectively revealed that the NLR34449 is
devoid of these broad spectrum genes. Further, screening of the parents with 120
markers showed 30 polymorphic markers, which covered almost all rice
chromosomes evenly. These polymorphic markers were used for background
selection in BC1F1. The two parents were crossed to produce F1. True F1s were
confirmed using gene-specific markers xa13prom (xa13), pTA248 (Xa21), xa5FS
(xa5) and backcrossed with NLR34449 to generate 200 BC1F1. In all, 126
phenotypically superior BC1F1 plants were selected from the 200 BC1F1s plants, based
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on the plant type similar to NLR34449 and further characterized for BLB resistance
employing molecular and phenotypic studies The BC1F1 plants were screened with
BLB gene-specific markers and 30 polymorphic markers for both foreground and
background selection, respectively. Out of 126 BC1F1 plants selected, 21 were found
to be positive for xa13, 18 were positive for Xa21, 32 were positive for xa5 gene,
whereas, 16 were double positive for both Xa21 and xa13, 13 were double positive for
both Xa21 and xa5, 15 were double positive for both xa13 and xa5. Interestingly, 9
BC1F1 plants with triple positive for Xa21, xa13 and xa5 genes were identified from
foreground screening. Further 9 selected BC1F1 plants were subjected to the
recombinant selection employing the closely located targeted 3 BLB genes to
minimize the linkage drag from RPBio226 at these loci. In background selection the
selected BC1F1 (three gene pyramid) plants were screened with 30 polymorphic
markers. Recovery percentage of recurrent genome was 76.7 – 83.3 % and exhibited
high levels of resistance against BLB. The BLB introgressed progeny BC1F1- 9 had
showed significant yield increase (31.5) over NLR34449 apart from very low disease
score (0.5-lesion length). However, BC1F1- 54 (20.6g); BC1F1- 79 (22.1); and BC1F-
82 (21.7) had recorded yield levels similar to donor parent. Hence, the BC1F1 plants
that are having high yield levels along with BLB tolerance and almost all recurrent
parent traits would be used to progress further generations to use as straight variety.
In conciusion, in the present investigation NLR34449 high yielding fine grain
variety susceptible to BLB disease and has been introgressed with three BLB genes
from RPbio226.
Description
D5724
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