Characterization of variability in Cercospora sojina K. Hara causing frogeye leaf spot and identification of resistant sources in soybean
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Date
2023-01-18
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CSK HPKV, Palampur
Abstract
The present investigation entitled “Characterization of variability in Cercospora sojina Hara causing frogeye leaf
spot and identification of resistant sources in soybean” was undertaken during Kharif season to study pathogen
isolation and culture production techniques, development of differential set, pathogen variability (morpho-cultural,
pathogenic and molecular), mating type distribution, evaluation of resistant sources, inheritance of resistance, and
biochemical basis of resistance against Cercospora sojina. Frogeye leaf spot of soybean (Glycine max (L) Merill)
caused by Cercospora sojina Hara emerged as most destructive disease in Himachal Pradesh as PDI recorded was
ranged between 0.00 to 95.56 per cent. Thirty isolates of C. sojina were collected from different locations of five
districts (Kangra, Mandi, Solan, Hamirpur and Bilaspur) representing 3 agro-climatic zones of Himachal Pradesh.
Isolations were done by using three different methods viz; inoculation by bits, inoculation by using moist-chamber
technique and inoculation by using toothpick method. Out of these, moist chamber technique was the most reliable as
most of the isolates were recovered by using this technique. Thirty isolates were identified as Cercospora sojina
based on symptomatology, morphological characters and confirmed with molecular characterization. Culture
technique for C. sojina was also standardized as the fungus was slow growing in nature. Among nine tested media,
PCDA (Potato Cellulose Dextrose Agar) was found best with 4g concentration of cellulose whereas FRCA (Flat Rice
Cellulose Agar) media (4g cellulose) was found best at 25 ± 1ºC to produce long conidia. The pathogen was found
variable on the basis of morpho-cultural variability. A differential set was finalized to study the virulence structure of
C. sojina. Initially sixty soybean lines were selected from 200 genotypes and tested against six isolates, out of which
25 soybean lines were selected as pre-differential set which was tested against all the 30 isolates of C. sojina and
finally a differential set of 10 lines was developed. On the basis of disease reaction on differential set C. sojina
isolates were grouped into 10 pathotypes. Virulence analysis of the pathotypes (PCS 1 – PCS 10) revealed that PCS 1
and PCS 2 were highly virulent whereas PCS 3, PCS 8 and PCS 10 were least virulent. Variability studies on
morpho-cultural, pathogenic and molecular characters categorized 30 isolates of C. sojina into 11, 10 and 6 groups,
respectively. There is no or less correlation among the three types of variability studies. Molecular variability was
also studied and analyzed with POPGENE analysis software which revealed that thirty isolates were divided into 2
populations on the basis of geography (Latitude and longitude) and there is substantial gene flow among the two
populations. There was occurrence of maximum variability within the population i.e.>90 per cent as PhiPT value
ranged between 0.004 - 0.127. Mating type distribution of 30 isolates of C. sojina was studied using MAT1-1 and
MAT1-2 primers which revealed the presence of both the idiomorph (MAT1-1 & MAT1-2) found in CSH09 isolate
revealed that population in Himachal Pradesh probably undergoing sexual reproduction. Out of a total two hundred
lines evaluated under field conditions 30 lines found resistant which were screened against diverse pathotypes (PCS1-
PCS-10) and four resistant lines viz.; Harder, JSM 285, CAT 195 and GP465 were identified as highly resistant
against all pathotypes. Biochemical basis of resistance was also studied in a resistant line ‘Himso 1685’ and a
susceptible line ‘Shivalik’ revealed that the tested enzymes i.e., Phenols, PPO and PO had no or less role in defence
as there may be other enzymes which can affect the defence mechanism upon infection in soybean against C. sojina.
Inheritance of resistance for C. sojina studied and results revealed that the inheritance was controlled by single dominant gene.