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20152
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Subject: Plant Pathology × End date: 2015 × Start date: 2015 × Type: Thesis × Thesis Type: Ph.D ×
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    ThesisItemOpen Access
    Population dynamics and pathogenic behaviour of Rhizoctonia solani Kühn in response to rice based cropping system of Punjab
    (PAU, 2015) Kipsumbai, Pixley Kiptui; Sekhon, P.S.
    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.
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    Management of Sheath Blight of Rice Using Native Strains of Biocontrol Agents and Cloning of Antifungal Gene
    (PAU, 2015) Heflish, Ahmed Ibrahim Abdelbary Ibrahim; Singh, Narinder
    Sheath blight of rice caused by Rhizoctonia spp. is one of the most important rice diseases worldwide including India. Thirty isolates of Rhizoctonia were isolated from infected rice plants. Genetic diversity of the pathogen was determined by using 11 simple sequence repeats (SSR) molecular markers. The isolates were identified with specific primers at species level. Twenty nine isolates were identified as Rhizoctonia solani while one isolate was found to be as Rhizoctonia oryzae. Native biocontrol agents were isolated from rice rhizospheric soils. Twenty seven isolates of Trichoderma and seventeen isolates of Pseudomonas fluorescens were isolated and screened in vitro against R. solani and R. oryzae causing sheath blight of rice through dual culture technique, effect of volatile and non volatile compounds. Among all tested isolates under in vitro conditions Trichoderma T19 showed the maximum inhibition for R. solani and R. oryzae (65.80 and 74.44 % respectively). Volatile metabolites from Trichoderma T19 also caused maximum inhibition of R. solani (56.91 %) and R. oryzae (91.23%). In case of non-volatile compounds inhibition of the pathogens increased with the increase of culture filtrate concentration from 10 to 50 per cent and T19 with 50 per cent concentration showed the highest percentage of inhibition against R. solani (95.80 %) and R. oryzae (90.74%). P. fluorescens (Pf14) reduced the mycelial growth of R. solani by 60.49 per cent (inhibition zone 9.67 mm) and of R. oryzae by 74.94 per cent with 12.78 mm inhibition zone. Volatile compounds from P. fluorescens (Pf14) showed inhibition of mycelial growth of R. solani and R. oryzae (76.79 and 66.79 % respectively), while in case of non volatile the inhibition by Pf14 using 50 per cent concentration of culture filtrate against R. solani and R. oryzae was 82.47 and 93.46 per cent respectively. Biochemical tests for estimation of cell wall degrading enzymes showed the ability of T19 and Pf14 to produce high level of chitinase (22.1 and 17.5 unit/ml respectively) and β-1,3-glucanase (1.92 and 1.76 unit/ml respectively). Pf14 also presented high activity of siderophore production (20.5 mm halo zone). Fingerprinting of the most effective seven isolates of Trichoderma and of P. fluorescens using SSR marker showed variation between the isolates at molecular level. Efficacy of talc based bioformulations of Trichoderma T19 and P. fluorescens Pf14 applied individually as well as in combination under greenhouse and field conditions was seen against sheath blight of rice. Trichoderma T19 when applied as seed + soil + foliar spray showed the maximum reduction of disease incidence (67.49 %) and disease severity (82.92 %). It also acted as plant growth promoter and increased the number of tillers/hill (12.20), plant height (72.71 cm) and finally the yield of the crop (71.3 q/ha). Molecular identification of Trichoderma T19 using ITS1 and ITS4 universal primers showed 100 per cent similarity with T. asperellum. Cloning of endochitinase42 gene from T. asperellum T19 (potent strain) and Trichoderma T5 (mild strain) showed no difference in the gene sequence between the two Trichoderma isolates, while the difference in the antagonistic activity may be was due to the difference in the promoter region of the gene. Study of shelf life of bioformulations revealed that antagonists T. asperellum T19 and P. fluorescens Pf14 can remain potent for 6 months when stored at room temperature, while at low temperature storage (4oC) these can remain potent up to one year. For mass multiplication sugarcane pressmud and rice leaves supported rapid, maximum growth and sporulation of T. asperellum T19.