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DEVELOPMENT OF RESISTANCE IN Pyricularia grisea (Sacc.) ISOLATES INDUCING RICE BLAST IN COMMONLY USED FUNGICIDES

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Title DEVELOPMENT OF RESISTANCE IN Pyricularia grisea (Sacc.) ISOLATES INDUCING RICE BLAST IN COMMONLY USED FUNGICIDES
 
Creator MOHAMMAD RAFI G
 
Contributor JAGADEESHWAR, R
 
Subject fungicides, fungi, pesticide resistance, crossing over, rice, concentrates, diseases, planting, tolerance, biological development
Pyricularia grisea (Sacc.)
 
Description Rice blast incited by Pyricularia grisea (telemorph: Magnaporthe grisea) is one of
the economically important disease of rice in Andhra Pradesh for which chemical control
by fungicides viz. carbendazim, tricyclazole, kasugamycin etc. was adopted as an integrant
measure to reduce its damage. Since the wide spread use of above systemic fungicides
began in recent past fungicide resistance in blast pathogen has become an important
problem in Southern Telangana Zone of Andhra Pradesh. keeping this in view Nine isolates
(Pg1 to Pg9) of P.grisea obtained from different rice growing areas of STZ of Andhra
Pradesh viz., Ranga Reddy, Mahabubnagar, Nalgonda were tested for in vitro for
development of resistance to carbendazim and tricyclazole.
The isolation of P. grisea was made from the infected leaf samples of rice in oat
meal agar medium by following standard tissue isolation procedure. The cultural characters
among isolates of P. grisea varied with respect to colony characters like type of growth,
colour of colony and colony margin. Colour varies with shades of grey, buff, black, greyish
black to dark jet black colour with smooth to irregular margin and medium to good growth
was observed. Pathogenecity of all the isolates of P.grisea collected was proved by
spraying spore suspension of 10-4 ml-1 on susceptible rice cv. HR-12. All the isolates
satisfied the Koch’s postulates and hence proved to be pathogenic on rice crop.
Sensitivity of P. grisea isolates to carbendazim was individually assayed in vitro at
different concentrations (0 - 2000 μg ml-1) in OMA. The test revealed that of the eight
isolates of tested Nalgonda isolate Pg9 recorded the lowest ED50 value of 2.82 μg ml-1 and
MIC value of 10 μg ml-1 which was nearly equal sensitive as reference isolate Pg2. Ranga
Reddy isolate (Pg1) recorded the highest ED50 value of 4.05 μg ml-1 and MIC of this isolate
was 10 μg ml-1. Ranga Reddy isolate Pg3 recorded the next lowest ED50 value of 2.98 μg
ml-1 with MIC of 10 μg ml-1 followed by Mahabubnagar isolates Pg4 with ED50 value of
3.32 μg ml-1 and Pg5 with ED50 value of 3.35 in the increasing order of their resistance.
The MIC values of both Mahabubnagar isolates Pg4 and Pg5 were 10 μg ml-1. Pg8 isolate
was recorded the next highest ED50 value of 3.6 μg ml-1 with MIC of 10 μg ml-1 followed
by Pg6 isolate (3.43 μg ml-1) and Pg7 isolate (3.39 μg ml-1) in the decreasing order of their
resistance. The MIC value for both Pg6 and Pg7 isolates was 10 μg ml-1. The results
indicates that the fungus is under high selection pressure leading to evolution of
carbendazim resistant population.
Sensitivity of P. grisea isolates to tricyclazole were individually assayed in vitro at
different concentrations (0 - 2000 μg ml-1) of tricyclazole in OMA. The test revealed that of
the eight isolates tested for their sensitivity to tricyclazole, Mahabubnagar isolate (Pg5)
recorded the highest ED50 value of 118.51 μg ml-1 and the MIC of isolate was 500 μg ml-1.
Ranga Reddy isolate Pg1 recorded the lowest ED50 value of 96.10 μg ml-1 and MIC value of
250 μg ml-1 which was nearly equal sensitive as reference sensitive isolate (Pg3). Pg4 isolate
collected from Mahabubnagar district recorded the next highest ED50 value of 110.41 μg
ml-1 with MIC of 250 μg ml-1 followed by Pg9 isolate (104.66 μg ml-1) and Pg8 isolate
(104.26 μg ml-1) both collected from Nalgonda district in the decreasing order of their
resistance. The MIC value for both Pg9 and Pg8 isolates was 250 μg ml-1. Isolate Pg2
recorded the next lowest ED50 value of 99.22 μg ml-1 with MIC value of 250 μg ml-1
followed by Mahabubnagar isolate Pg6 with ED50 value of 101.81 μg ml-1 and Nalgonda
isolate (Pg7) with ED50 value of 104.26 in the increasing order of their resistance. The
MIC values of both Pg6 and Pg7 were 250 μg ml-1. The results showed that the fungus is
under high selection pressure leading to evolution of tricyclazole resistant population.
Development of resistance towards carbendazim has contributed to the development
of positive cross resistance to both azoxystrobin and kresoxim-methyl whereas, its
resistance was unaltered to tricyclazole+mancozeb and pyraclostrobin+metiram. Similarly,
development of resistance towards tricyclazole had also contributed to development of
positive cross resistance towards tricyclazole+mancozeb whereas, its resistance was
unaltered to other fungicides viz., azoxystrobin, pyraclostrobin+metiram, and kresoximmethyl.
 
Date 2016-06-09T13:40:59Z
2016-06-09T13:40:59Z
2011
 
Type Thesis
 
Identifier http://krishikosh.egranth.ac.in/handle/1/67107
 
Language en
 
Relation D8873;
 
Format application/pdf
 
Publisher ACHARYA N.G. RANGA AGRICULTURAL UNIVERSITY