MSc

Sheath blight of rice is a major threat to rice cultivation causing huge yield loss. Realizing the practical importance, an investigation entitled “Integrated management of sheath blight disease of rice” was carried out during 2013-2014 with the objective of developing an integrated management strategy for sheath blight using liquid organic formulations, vermicompost and selected new generation fungicides.
A series of surveys were conducted in ten locations of Thrissur district during virippu season of 2013 to study the occurrence of sheath blight in two farmer preferred popular varieties namely Uma (MO-16) and Jyothi (PTB-39). Per cent Disease Severity (PDS) was found to be maximum in paddy fields of Adat (85.53) and Chalakudy (84.30) followed by Pudurkara, Irinjalakuda and Mannuthy. Per cent Disease Incidence (PDI) and Per cent Disease Severity (PDS) of sheath blight in ten rice growing locations of Thrissur district ranged from 24.53 to 51.95 and 44.76 to 85.53 respectively.
Characterization of ten isolates of the pathogen (Rhizoctonia solani) was done on four different solid media viz., Potato Dextrose Agar (PDA), Rose Bengal Agar (RBA), Czepck's Dox Agar (CDA) and Richard’s Agar (RA). Colony characters, sclerotial characters and growth rate of the ten isolates showed high diversity in different solid media. Based on these characters, cluster analysis was done by using the Unweighed Pair Group Average Method (UPGMA) isolates were grouped into two clusters A and B based on cultural characters. In cluster A, highest similarity coefficient of 0.69 was recorded. Cluster A was further divided in to two sub clusters A1 and A2. In sub cluster A1, the highest similarity coefficient of 0.78 was recorded. Cluster B had no sub clusters and it showed the similarity index of 0.67.
Enumeration of microbial load from three liquid organic formulations at different storage period revealed that microbial profile of bacteria, and Pseudomonas spp. in all the three liquid formulations ranged from 93.66 - 95.0 and 88.0 –89.66 × 105 cfu/ml respectively upto 120 days. At 210 days of storage, a slight decrease of bacterial population and increase in the number of fungal population from 34.0 to 42.0 × 104 cfu/ml was noticed. So, these liquid organic formulations can safely be stored up to 120 days without loosing its viability.
In vitro studies of various liquid organic formulations revealed that Jeevamrutha at 10 per cent concentration showed maximum inhibition of 85.18 per cent which was on par with Jeevamrutha 20% (79.62). Among the different new generation fungicides tested in vitro, Flusilazole 40 EC (0.15 %) and (Iprodione 25 WP + Carbendazim 25 WP) (0.15 %) showed 100 per cent inhibition against R. solani.
Based on the in vitro studies, field experiment were carried out and have come out with an encouraging new array of management practices for combating sheath blight of rice. The promising treatments to manage the disease were: (T10) Panchagavya 3% at 45 DAT + Flusilazole 40 EC (0.15%) at 60 DAT (T1) Panchagavya 3% at 45 & 60 DAT (T13) Jeevamrutha 20% at 45 DAT + (Iprodione25WP + Carbendazim 25WP) (0.15%) at 60 DAT (T7) Vermicompost @ 2.5 t/ha as basal +Jeevamrutha 20% at 45 & 60 DAT (T11) Panchagavya 3% at 45 DAT + (Iprodione 25 WP + Carbendazim 25 WP) (0.15%) at 60 DAT. These treatments gave high yield and net returns as evidence by the B:C ratios.