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Population structure of Xanthomonas oryzae pv. oryzae, the pathogen of bacterial blight of rice, from major rice growing areas of U.S. Nagar( Uttarakhand)

KrishiKosh

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Title Population structure of Xanthomonas oryzae pv. oryzae, the pathogen of bacterial blight of rice, from major rice growing areas of U.S. Nagar( Uttarakhand)
 
Creator Pandey, Shailesh
 
Contributor Kumar, J.
 
Subject population dynamics, Xanthomonas oryzae pv. oryzae, plant pathogens, bacterial diseases, blight, rice, tarai, Uttarakhand
 
Description Thesis-PhD
Bacterial leaf blight (BLB) of rice caused by Xanthomonas oryzae pv. oryzae (Xoo) is a major constraint for rice production in India, Nepal, Philippines, Bangladesh, Japan and other rice growing countries in Asia. The disease may incur over 65 to 95% yield reductions in the severely infected rice fields. Breeding and deployment of resistant cultivars carrying major resistance (R) genes has been the most effective approach to control BLB. However, to achieve successful deployment of resistant genes knowledge of the pathogen-population structure is a prerequisite. The present study was, therefore, designed to decipher the extent of genetic diversity and pathogenic variability of the population of Xoo prevalent in district Udham Singh Nagar (U.S. Nagar) by using PCR-based DNA fingerprinting and virulence grouping of the pathogen strains on the basis of their interaction with near-isogenic rice lines. Several sudden outbreaks in different rice growing areas of U.S. Nagar in the recent past necessitated such a study so as to have a guided and sustained management of this disease.
A total of 606 strains were generated from infected leaf samples collected from 15 locations during two years of disease surveys, i.e. 2007-2008 and 2008-2009. Both the PCR analyses detected approximately equal numbers of haplotypes and a strong correlation was found between the dendograms generated by both the PCR techniques. The phylogenetic relationship was better explained by IS primers (especially JEL1 and JEL2). A total of 46 molecular haplotypes grouped into seven lineages were detected indicating that the Xoo population prevalent in this area is genetically heterogeneous. One hundred fifty strains collected from a severely blighted field (location Haldi) were differentiated into seven haplotypes. Of these four haplotypes were grouped into lineage1. Eight haplotypes were detected among strains collected from Gadarpur which were grouped into two robust clusters, indicating the presence of clonal lineages. Lineage1 also dominated in Gadarpur. Haplotype 3 (lineage1) was found in majority of the areas suggesting migration. Haplotypes of other lineages viz., 2,3,4,5,6 were detected during both the years. Lineage 7 was detected only in Pratappur during 2008-2009. Varietal differences exerted strong influence on the Xoo population as indicated by the presence of different lineages on different varieties. Diversity value of Xoo population from improved and traditional cultivars was the same indicating that host diversity did not affect pathogen diversity. Genetic diversity estimates of both the years were greater than 0.90 indicating high diversity in Xoo population. These high values suggest the need to deploy rice varieties with diverse sources of resistance.
Virulence typing of 48 Xoo strains representing 24 distinct banding patterns on IRRI near-isogenic lines detected 11 pathotypes. Pathotype 1 defeated all the single major resistant genes except Xa21. A strong qualitative complementation effect was clearly identified at a digenic level i.e xa5+Xa21. Near-isogenic line-strain interaction was highly significant (P≤ 0.01), confirming the pathogenic specialization of Xoo population prevalent in U. S. Nagar. The molecular polymorphism observed among Xoo strains was largely independent of virulence polymorphism (r=0.21962). Pathogenicity association analysis showed zero VAC value with Xa21. Xa21 alone and two gene pyramids possessing Xa21 as one of the member showed values (VAC=0,VF=0 and PAC=1), suggesting the incompatibility of Xa21 and gene pyramids towards all the strains tested. Xoo strains are prevalent that can overcome resistance offered by Xa21 in many regions in India. Further, quantitative complementation effect was identified after measuring the lesion length on NILs with Xa21 alone and in combination with xa5 after 30 days of inoculation. High HTvalues suggest the need to deploy rice varieties with different sources of broad resistance, because breakdown of resistance involving highly diverse pathogen would be predicted to occur at a faster rate. Keeping aforesaid facts in mind, deployment of a pyramid of resistance genes Xa21+ xa5 or Xa21+xa13 appears to be the right strategy for management of bacterial leaf blight in U.S. Nagar.
 
Date 2016-08-01T15:26:16Z
2016-08-01T15:26:16Z
2010-08
 
Type Thesis
 
Identifier http://krishikosh.egranth.ac.in/handle/1/70417
 
Language en
 
Format application/pdf
 
Publisher G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)