BSc-MSc (Int.)

Bacterial leaf blight (BLB) in rice caused by Xanthomonas oryzae pv.
oryzae(Xoo) is one of the most destructive epidemic of rice throughout the
world and widespread in Asia, especially in South East Asian countries like
India. Durable and effective resistance against BLB can be attained by
pyramiding resistance genes into the genetic background of BLB
susceptible popular rice cultivars. In the present study entitled
“Assessment of recurrent parent genome in the two/ three R genes
pyramided lines of the rice variety Aiswarya through genome wide marker
assay.” was undertaken at the Department of Seed Science and
Technology, College of Agriculture, Vellayani, Thiruvananthapuram to
estimate the recurrent parent genome recovery in BC2F4lines pyramided
with BLB resistance genes, viz., Xa21, xa13 and xa5 from the donor variety
Improved Samba Mahsuri (ISM) in to the genetic background of rice
variety ‘Aiswarya’.
DNA markers, pTA248, xa13pro and xa5FM tightly linked to the BLB
resistance genes Xa21, xa13 and xa5 respectively were used for the
selection of lines with two or three resistance gene combination in the
BC2F4 lines in foreground screening. The comparison of allele sizes of
amplicons of these markers in BC2F4 lines with that of both the parents
confirmed the presence or absence of the marker associated with respective
gene of resistance.
Foreground selection was performed initially on 50 BC2F4 plants to
identify the presence of the three R genes for BLB resistance. Xa21 gene
was shown to be fixed in all the plants. A total of five plants were found to
be homozygous for xa13 gene and another five was shown to be
heterozygous for the gene. One BC2F4 line had the three genes xa5, xa13
and Xa21 in homozygous condition.
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Background screening was done in four plants (Ai- 543- 7- 10- 11, Ai- 543- 7- 10-
16, Ai- 543- 7- 10- 18 and Ai- 543- 7- 10- 24) with the homozygous two gene
combination of Xa21 and xa13 and the one plant (Ai- 543- 7- 10- 10) with homozygous
three gene combination. 150 genome wide SSR markers specific to Aiswarya had been
identified in the previous studies. In BC2F2 generation, 140 out of 150 had been fixed in
homozygous condition. The remaining 10 markers (RM4B, RM110, RM190, RM214,
RM271, RM277, RM313, RM447, RM502 and RM517) were used in this study.
The percentage of recurrent parent genome (RPG) recovery was calculated based on
the results of background screening. The highest recurrent parent genome recovery of
96% was observed in the lines Ai-543-7-10-16 and Ai-543-7-10-24. The line Ai-543-7-
10-10 with three gene combination showed 95.67% recovery of genome as in the rest of
the lines screened (Ai-543-7-10-11 and Ai-543-7-10-18).
The present could study identify BC2F4 lines Ai-543-7-10-16 and Ai-543-7-10-24
plants with homozygous two and three R gene combination with more than 95%
recurrent parent genome recovery. These lines can be forwarded by self pollination and
with stringent screening on the morphological traits of the recurrent parent to develop
Essentially Derived Variety for Aiswarya with durable resistance to BLB.