Population dynamics and pathogenic behaviour of Rhizoctonia solani Kühn in response to rice based cropping system of Punjab
Loading...
Date
2014
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Punjab Agricultural University
Abstract
Present investigations were undertaken to study the R. solani population dynamics and pathogenic
behaviour under different crop rotations, AG groups and the extent of genetic differentiation and host
specialization between infecting populations in different hosts. By using species specific primers the
occurrence of Rhizoctonia species was analysed and were identified as R. solani (87.8 %), 11.1% were
R. oryzae-sativae and 1.1 % R. oryzae admixed infection with R. oryzae-sativae. Rhizoctonia solani was
characterized morphologically as well as at molecular level, which showed presence of high degree of
variation among these R. solani isolates. The R. solani isolates were further grouped into anastomosis
groups (AGs) by AG subgroups specific primers and it was established that most potato isolates were
AG3 and AG2-1. Rice and maize isolates were mostly grouped into subgroup AG1-1A. R. solani rice
isolates were studied for their aggressiveness on six rice genotypes and the aggressiveness response of
these isolates were further analysed by Mahalanobis D2 analysis and two major groups were observed.
Out of all the R. solani isolates, nearly 20% were found to be highly aggressive. Cross infectivity
studies revealed that R. solani isolates were cross pathogenic to other hosts except potato and cotton
isolates which were not able to cause any disease symptoms on rice. But R. solani isolates were found to
be more virulent on their host of origin than any other host under test except in chilli isolate (Cl-40) was
found to be highly adaptive to all hosts. Three cropping patterns and 17 R. solani isolates were tested to
study the pathogenic behaviour and population dynamics of R. solani isolates under fixed sick plots. A
significant interaction was observed between the R. solani isolates and the crops grown in these three
adopted cropping systems. The least population build–up after two years of rotation was recorded in the
potato-spring maize-Basmati rice cropping system. The overall mean of rice isolates in this system was
44.7 CFU/g of soil, while it was high in the cropping pattern comprising potato –moong bean-rice and
wheat ie. 68.1 CFU/g of soil. To find out development of resistance, eighty five out of total 99 isolates
under test showed sensitive reaction to propiconazole below 50 ppm concentration in vitro. Only ten
isolates showed growth inhibition at 100 ppm and four R. solani isolates were least responsive and
showed growth inhibition at 250 ppm concentration. All the isolates were found to be sensitive in their
reaction to pencycuron when compared with Tilt 25EC. The ED90 values for most of the insensitive R.
solani isolates were found to be in the range of 14 to 26 ppm for pencycuron and 10 to 78 for
propiconazole. These preliminary studies indicated that there is development of fungicide resistance in
R. solani rice sheath blight isolates as only partial disease control at 0.1% spray concentration of Tilt
25EC was recorded. As no fungicide is recommended for seed treatment in wheat so the two fungicides
namely propiconazole and pencycuron were tried and found effective in controlling seed rot and
seedling mortality in R. solani sick pots. At the molecular level using interspecific sequence repeat
primers, a total number of 79 R. solani isolates were analysed and were divided into three major groups
(I, II, III). There was partial relationship observed between the level of aggressiveness of the isolates on
rice and phylogenetic groups generated by the ISSR markers