Management of brown spot disease of rice using fungal root Endophyte Piriformospora indica and new generation fungicides

Abstract

A study entitled ‘Management of brown spot disease of rice using fungal root endophyte Piriformospora indica and new generation fungicides’ was conducted during 2017-19 at Department of Plant Pathology, College of Agriculture, Vellayani with the objectives to evaluate the effect of root endophyte Piriformospora indica against brown spot disease of rice caused by Helminthosporium oryzae and evaluation of new generation fungicides viz., strobilurins, azoles and their combinationsfor the management of brown spot disease of rice. A survey was conducted in rice fields of six KAU stations during 20182019 to collect the infected leaf samples and to assess the disease incidence (DI) and severity (Percent Disease Intensity (PDI)). Among the surveyed locations, maximum DI (76%) and PDI (64.6%) were recorded from IFSRS Karamana whereas the disease was absent in RARS Kumarakom due to the complete crop failure. H. oryzae was isolated from the collected specimens; a total of five pure cultures of H. oryzae (Isolate 1 to Isolate 5) were obtained and Koch’s postulates were proved for all the isolates in rice var. Uma. All the H. oryzae isolates were screened for its virulence and pathogenicity in rice var. Uma. The isolate 5, from IFSRS Karamana, produced the symptom within 24 h of inoculation. On 5th day of leaf inoculation, isolate 5 recorded maximum PDI of 62.22 per cent with a maximum lesion size of 2.94 cm; and thus concluded as the most virulent isolate. Dual culture assay of P. indica and H. oryzae in potato dextrose agar (PDA) medium indicated that the beneficial root endophytic fungus significantly inhibited the growth of the pathogen through multiple antagonistic properties viz., lysis / inhibition zone (0.65 cm) and antibiosis (0.37 cm). Maximum growth inhibition of H. oryzae (54.44 %) by P. indica was observed on 7th day of dual culturing. P. indica-primed rice seedlings and plants (var. Uma) could significantly delay the symptoms of H. oryzae up to eight days after inoculation (DAI) of the pathogen. The primed seedlings and plants recorded the lowest lesion size (67.87 and 63.6% over control respectively) at seven DAI and the highest disease suppression (87.6 and 80.3 % over control respectively) at 15 DAI. P. indica-root colonization in rice seedlings resulted in enhanced growth with increased root and shoot biomass. P. indica-colonized roots had more number of secondary and tertiary roots with profuse root hairs. There was two-fold increase in shoot and root fresh weight and three-fold increase in shoot dry weight and 2.3 fold increase in root dry weight. The above experiments were done in CRD with five replications. In vitro evaluation of selected new generation fungicides viz., tebuconazole 25.9 EC, difenoconazole 25 EC, azoxystrobin 23 EC, pyraclostrobin 20 WG, pyraclostrobin 20 WG + tebuconazole 18.3 SC, azoxystrobin (11%) + tebuconazole (18.3%) SC at 10, 50,100 and 250 ppm against H. oryzae in PDA by poisoned food technique revealed that all the selected fungicides significantly reduced the growth of H. oryzae. Combination fungicides were more effective in inhibiting the growth of H. oryzae. The highest inhibition was observed in pyraclostrobin 20 WG + tebuconazole 18.3 SC at different concentrations tested; and at 100 and 250 ppm, there was complete inhibition of mycelial growth of the pathogen followed by azoxystrobin (11%) + tebuconazole (18.3%) SC. Based on the results of in vitro evaluation, a pot culture experiment was conducted with rice var. Uma to evaluate the efficacy of the best azole fungicide (tebuconazole 25.9 EC), best strobilurin fungicide (pyraclostrobin 20 WG) and their combinations (pyraclostrobin 20 WG + tebuconazole 18.3 SC and azoxystrobin (11%) + tebuconazole (18.3%) SC at 0.05 and 0.1 per cent against brown spot disease of rice in CRD with three replications. All the tested fungicides significantly reduced the lesion formation and development in leaves. Minimum lesion size of 0.84 cm and 1.17 cm was recorded in azoxystrobin (11%) + tebuconazole (18.3%) SC and pyraclostrobin 20 WG + tebuconazole 18.3 SC respectively. Similarly, the maximum disease suppression of 81.30 per cent and 77.50 per cent over control was recorded with azoxystrobin 11 + tebuconazole 18.3 SC at 0.1% and pyraclostrobin 20 WG + tebuconazole 18.3 SC at 0.05% respectively. The results clearly indicated the curative action of azole, strobilurin and its combination fungicides. Thus, the present study revealed that brown spot of rice could be effectively managed by root colonization of rice seedlings with the beneficial root endophytic fungus, P. indica or foliar spraying of azoxystrobin 11% + tebuconazole 18.3% at 0.1% or pyraclostrobin 20 WG + tebuconazole 18.3 SC at 0.05%. The results may be subjected to multi-location and multi-seasonal field trials before recommendation. The compatibility of P. indica with new generation fungicides and the residue of fungicides in grains may further be studied.