Evolving high yielding rice genotypes with durable resistance to bacterial leaf blight (BLB) is pertinent considering the extensive damage caused by the disease in most of the rice growing regions. Two high yielding BLB susceptible indica rice cultivars, ÔADT43Õ and ÔASD16Õ popular among farmers and consumers across South India have been introgressed with three BLB resistance genes xa5, xa13 and Xa21 from isoline IRBB60 using functional markers. The F 2 populations of 500 plants from ADT43 · IRBB60 and 806 plants from ASD16 · IRBB60 crosses were screened for the presence of all the three resistance genes. Thirty genotypes with three genes in homozygous and 55 genotypes with two genes in homozygous and one gene in heterozygous condition were identified. These pyramided genotypes with two or three resistance genes exhibited high levels of resistance against two predominant Xanthomonas oryzae isolates of South India. Among the 30 pyramided genotypes (xa5 + xa13 + Xa21), 12 were found to be significantly high yielding with desirable agronomic characteristics and the selection efficiency of the present markers was hundred percent.
The mixture of Pseudomonas fluorescens isolate Pf1 and Py15 and Bacillus subtilis isolate 16 (Bs16) was found to protect mulberry plants from root rot disease caused by Macrophomina phaseolina. Induction of defense-related proteins and chemicals by the mixture of Pf1, Py15 and Bs16 against challenge inoculation with M. phaseolina in mulberry were studied. The activity of defense enzymes peroxidase (PO), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), b-1, 3-glucanase, chitinase and defense chemical total phenols were found to be significantly higher in combined application of biocontrol agents Pf1'Py15'Bs16 followed by Pf1'Bs16, Pf1'Py15 and Py15'Bs16 treated plants when compared to individual treatments and control. The SDS-PAGE analysis of protein in biocontrol agents treated plant showed eight proteins with molecular weight of 14, 23, 30, 35, 45, 50, 60 and 98 kDa. In healthy plants only six proteins (excepting 14 and 98 kDa) appeared in biocontrol agents treated plant two additional new proteins appeared. These results suggest that induction of defense enzymes involved in phenyl propanoid pathway and accumulation of total phenols and PR-proteins might have contributed to restriction of invasion of M. phaseolina in mulberry roots.
Marker assisted selection was employed to pyramid three bacterial blight resistance genes Xa21, xa13 and xa5 into high yielding susceptible rice cultivars ADT43 and ADT47. With the assistance of PCR markers, homozygous and heterozygous genotypes were identified in F 2 generation of two crosses (ADT43 6 IRBB60 and ADT47 6 IRBB60) and goodness of fit was tested. Eighty nine plants from F 3 generation of ADT43 6 IRBB60 were also screened for resistance genes. The genotypes carrying resistance genes in different combinations were identified. The pyramided lines showed a wider spectrum and higher level of resistance against two Xoo isolates under field conditions.
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