BSc-MSc (Integrated)

Bacterial leaf blight disease caused by Xanthomonas oryzae pv. oryzae
(Xoo) is a major constraint in major rice growing areas of the world particularly
in Asia. The disease is prelevant in the kharif season and it results in a greater
yield loss. Since there is no valid chemical control measure, exploiting host
plant resistance is an efficient way to tackle this problem. Approximately 40
genes conferring resistance to BB were identified. Pyramiding of these genes
into the background of susceptible parent with good agronomical traits is the
best strategy that can be adopted to develop plant varieties durable resistance to
BB. So the present study entitled “Genome wide marker assay for the
recovery of recurrent parent genome in rice (Oryza sativa)” was undertaken in
College of Agriculture, Vellayani, Thiruvananthapuram to estimate the
reconstitution of genome of Aiswarya (RP) rice variety in the BC2F1 plants
pyramided with genes for resistance to Bacterial leaf blight through molecular
markers covering the entire genome of Aiswarya.
DNA markers closely linked to the BB resistance genes,viz.,xa13 pro
(xa13gene), pTA248 (Xa21gene), RMWR7.1 (Xa33gene) were used for
validation of the marker polymorphism in the donors for the genes. Improved
Samba Mahsuri with xa13 and Xa21, Samba Mahsuri with Xa33, were taken as
donors and Aiswarya was chosen as the recipient parent. The validation of gene
specific markers confirmed the absence of the genes in the recurrent parent used
in the study. And these markers were further used for foreground selection in
BC2F1 plants.
Also, the donor and recurrent parents used in the study were screened with
320 SSR primers in order to find the markers specific to the recurrent parent. In
this screening out of 320 markers used, 44 were found to be polymorphic and
these polymorphic markers were used in the background selection.
Foreground selection was performed initially in all the 149 BC2F1 plants to
identify the presence of these genes. In the foreground selection, a total of 149
plants were screened and 79 plants were found to have xa13 gene and 38 plants
confirmed the presence of Xa21 gene while none of the screened plants showed
the presence of Xa33 gene. 23 plants were found to possess two gene
combinations of xa13+Xa21 and these plants were subjected to background
selection to estimate the percentage introgression of the recurrent parent genome.
Background screening of the plants identified with two gene combination
using the 44 markers specific to recurrent parent revealed the number of markers
showing homozygosity and heterozygosity with the recurrent parent. With this
information percentage recovery of RPG was calculated and found that among 23
plants, the maximum recovery found was 84.09% and a total of 5 lines were
showing more than 80% recovery of recurrent parent genome.
The present study could identify BC2F1 plants identified with xa13 and
Xa21 with genome recovery of more than 80% and further screening can be done
in the BC2F2 generation to develop Essentially Derived Variety.