PhD

The present study on ‘Bio intensive Management of Blast Disease of Rice (Oryza sativa L.)’ was conducted at College of Agriculture, Vellayani and Regional Agricultural Research Station, Pattambi during 2008-2010. A survey conducted during kharif and rabi seasons 2008, in six panchayats from three different blocks, in Palakkad district, revealed that maximum disease incidence was in Pattithara panchayat during rabi and maximum disease severity was in Chalissery panchayat during kharif. The disease intensity and severity were high during kharif season, than rabi and in all the panchayats disease incidence occurred, 60 days after sowing.
The fungus produced symptoms on leaves and neck of panicle. Sixty isolates from leaf samples were obtained from the six panchayats which proved the Koch’s postulates. After preliminary screening, thirteen isolates out of the 60 were selected. Out of the thirteen isolates, five isolates, P2, P4, P5, P9 and P12 had high virulence and these were selected for further studies. Among the five isolates the most virulent isolates like P4, P2 and P12 were having dark black coloured colonies with good growth. The isolate from Chalissery (P4) which was highly virulent, with maximum radial growth, mycelial dry weight, conidial size, and sporulating nature was selected for further studies. The isolate was tentatively identified as Pyricularia oryzae and further confirmed at IARI, New Delhi with accession number, as ITCC-7019.
Among the media tested Potato Dextrose Agar was best followed by Oat Meal Agar. Among the liquid media, the Potato Dextrose broth supported maximum growth of Pyricularia. The optimum range of temperature for growth of Pyricularia was 25 – 30 °C, and pH value for maximum growth was 6.5.
The most potent fungal antagonist Trichoderma sp. was obtained from Kadambazhippuram panchayat and the bacterial antagonist fluorescent pseudomonad was obtained from Thrithala panchayat.
The per cent of inhibition was highest for Trichoderma sp. under in vitro conditions and hence this culture was selected as the fungal antagonist for further studies. The hyphae of the Trichoderma were found to coil around the hyphae of blast pathogen and in some areas disintegration of pathogen hyphae were also observed. Based on the morphological characteristics of the fungal antagonist the isolate was tentatively identified as Trichoderma harzianum and further confirmed at IARI, New Delhi, with accession number, as ITCC-7018.
The fluorescent pseudomonad with highest percentage of inhibition was selected as bacterial antagonist for further studies. Based on the morphological, cultural, biochemical and physiological characteristics, the bacterial antagonist has been tentatively identified as Pseudomonas fluorescens biovar - 1.
Among the plant products, the percentage of inhibition on the growth and spore germination of Pyricularia oryzae was significantly higher for the Palmarosa oil @ 0.5ml/ l) under in vitro conditions. Neemazal @ 5ml/ l was the second best plant product. The percentage reduction of spore germination was also highest for Palmarosa oil followed by Neemazal.
Carbendazim (1.5g/ l), followed by Propiconazole (1ml/ l) were the best performing fungicides under in vitro conditions and they were selected as the best two chemical fungicides for further studies. Two blasticides viz., Isoprothiolane (1.5ml/ l) and Carpropamid (1ml/ l) were also selected as additional treatments.
Salicylic acid (0.1ml/ l) and Benzoic acid (0.1ml/ l) were selected as best two resistance inducers from the pot culture experiment – I, since they reduced the disease severity significantly and increased the yield.
In pot culture experiment-II, plants treated with Palmarosa oil + Carbendazim (T23) had significantly reduced the blast disease. Next best performance was when Salicylic acid combined with Pseudomonas fluorescens or Trichoderma. The two biocontrol agents, Pseudomonas fluorescens and Trichoderma were effective when individually combined with plant products like, Palmarosa oil, or Neemazal, or resistance inducer, Salicylic acid. The biometric observations like, height of the plant, number of total and productive tillers, grain yield and straw yield were also considerably higher for the above treatments. The best nine treatments with lowest PDI and highest yield from this experiment were selected for field experiments.
Palmarosa oil and Neemazal was compatible with Trichoderma, but the systemic fungicide, Carbendazim inhibited growth of Trichoderma followed by Propiconazole. Pseudomonas fluorescens was compatible with the two plant products, Palmarosa oil and Neemazal as well as two fungicides, Carbendazim and Propiconazole. It was also found that T. harzianum and Pseudomonas fluorescens were compatible to each other.
Field Experiment-I showed that 75 DAT, T23 (Palmarosa oil + Carbendazim) had significantly lowest percentage of disease incidence and this was on par with T21 (Palmarosa oil + Salicylic acid), T36 (Trichoderma + Pseudomonas fluorescens + Salicylic acid) and T34 (Trichoderma + Pseudomonas fluorescens + Palmarosa oil). The treatment T23 (Palmarosa oil + Carbendazim) had the highest effect on reducing the PDI, 75DAT along with four treatments viz., T21, T27, T36 and T34 which were on par in their effects.
The treatment T23 (Palmarosa oil + Carbendazim), produced significantly more height, higher number of total tillers, and productive tillers. Significantly higher grain yield /ha was obtained for T23 and T34. Significantly maximum straw yield /ha was also obtained for T23
In the diseased plants there was a steady decrease in chlorophyll ‘a’, ‘b’ and total chlorophyll. But in the uninoculated healthy plants, chlorophyll content remained same throughout the observation period. The activity of defense related enzymes viz., peroxidase, poly phenyl oxidase and phenyl alanine ammonia lyase activity, was significantly higher in rice plants on 5th day after inoculation for the treatment Trichoderma + Pseudomonas fluorescens + Palmarosa oil followed by Trichoderma + Pseudomonas fluorescens + Salicylic acid. Enzyme activities were least in the un inoculated plants.
In the second experiment (kharif 2010) 75DAT, T23 (Palmarosa oil + Carbendazim) had significantly lower percentage of disease incidence. Two additional blasticides were also on par with T23 The biometric observations also followed the same trend. Significantly maximum grain yield and straw yield /ha was obtained for T23.
The pooled analysis during two succeeding years, (kharif 2009 and 2010) revealed that, T23 had the lowest PDI with highest efficiency in reducing the blast disease. Four treatments viz., T21, T27, T36 and T34 which were on par in their effects, with T23.
The B:C ratio was highest for T23 (Palmarosa oil + Carbendazim) followed by T21 (Palmarosa oil+ Salicylic acid), T27 (Neemazal + Carbendazim) (2.5), T34 (Trichoderma + Pseudomonas fluorescens + Palmarosa oil), T36 (Trichoderma + Pseudomonas fluorescens +Salicylic acid) and fungicidal check T41 (Tricyclazole). Exactly the same value of the maximum B:C ratio was obtained for Isoprothiolane.
The relationship between blast disease severity and weather factors during kharif 2010, indicated positive correlation between disease severity and maximum temperature, relative humidity, rainfall, and number of rainy days but negative correlation with minimum temperature.
The outcome of this research work which can be recommended in the rice organic farming techniques, are the following
1. Trichoderma + Pseudomonas fluorescens + Palmarosa oil
2. Trichoderma + Pseudomonas fluorescens +Salicylic acid
3. Palmarosa oil + Salicylic acid
The result of molecular diagnosis of five selected cultures of blast pathogen, based on the D1/D2 regions in PCR analysis showed 99% similarities for 4 cultures (P2, P4, P9 and P12) and 97% similarities in one culture (P5) with the Magnaporthe oryzae, which accurately proved the identity of blast pathogen.