Rice blast

Rice blast, caused by Pyricularia oryzae Cav. (Magnaporthe grisea Sacc.), is an important and serious disease and a major constraint to rice production worldwide 1. The pathogen, a holomorph of a complex of heterothallic Ascomycetes, is able to infect more than 50 different grass species and is one of the most damaging of rice diseases 2. It is estimated that rice blast is responsible for approximately 30% losses of rice production which is equivalent of feeding 60 million people globally 3 thus major threat to global food security 4. In India, rice blast is a major production constraint in irrigated ecosystem 5 and under severe epiphytic conditions may result a loss of 70–90% 6.In central India the blast diseases causes significant loss in yield in traditional as well as improved varieties. The scented rice Basmati with a wide popularity among the growers has even no resistance to diseases 7 and shows high level of susceptibility under conducive weather conditions 8. The management of blast disease using chemicals is common as, the risk of the disease highly influence grain yield and requires a judicious use of fungicides 9. However the use of chemicals resulted in environmental pollution and ill health to biotic community as a whole, and this necessitates developing natural product as alternative to synthetic fungicides to control the disease 10. The botanicals that are target-specific, biodegradable and relatively safe to non-target organisms should be a best alternatives. Moreover, they are more compatible with components of the environment than the chemical owing primarily due to their susceptibility to degradation by heat, light and microorganisms 11 and worth as they are economical and feasible 12.The management of rice blast using botanicals has been reported to be significantly effective 13,14,15. The objective of this research is to evaluate the efficacy of botanicals for leaf blast management and enhancing the yield traits of rice under irrigated ecosystem.
MATERIALS AND METHODS
The field trials were laid out in a randomized block design (RBD) with three replications in each. The experiment was conducted at Agricultural land, Rewa (24’18 and 25’12 north latitudes and 81’2 and 82’18 east longitudes), Madhya Pradesh, India during rainy season 2012 and 2013. Blast susceptible variety “Basmati” was transplanted in a plot of 5m x 3m size at 15cm x 15cm spacing. Fertilizers were applied @ 80:60:40 kg ha-1 of N, P2O5 and K2O respectively. Seven commercially derived botanicals with azadiractin as active ingredients viz. Achook 5ml l-1(Azadirachtin 0.15% a.i) , Biotos 2.5ml l-1(Plant activator-Monoterpenes a.i.), Neem Azal T/S 3.5ml l-1 (Azadirachtin a.i), Neem gold 5ml l-1(Azadirachtin 0.15% a.i), Spictaf 4.5ml l-1 (Azadirachtin a.i), Tricure 5ml l-1 (Azadirachtin 0.03% a.i) and Wanis 5ml l-1(Plant activator-Monoterpenes a.i.), along with two standard fungicides Bavistin 1g l-1 (Carbendazim 50% WP a.i.) and Hinosan1g l-1 (Ediphenphos 50% EC a.i.) were evaluated, over control. Three sprays of plant-derived commercial products were carried out at ten days interval, starting with the incidence of the disease. Disease incidence was recorded firstly at initial stage before spraying the products, secondly after one week and finally at harvest. Five plants from each plot were randomly selected and from each selected plants, three leaves were selected for recording disease index. The disease incidence was recorded by using 0-9 scale 16 at weekly interval and percent disease index (PDI) was calculated using the formula.

The observations of yield contributing characters viz. Plant height, tiller numbers, number of spikelet and panicle length were determined at harvest.
Percent increase in yield (PIY) was calculated by the following formula

Percent increase in seed weight was determined by the formula
(Seed weight in treatment-seed weight in control)/(seed weight in control) x100
Statistical analysis
All data in tables are shown as means of three replicates. Two -way ANOVA was used for statistical analysis and Fisher’s test was adopted to detect the significant difference between the means of different treatments. All statistical analyses were done using the Excel 2007.
RESULTS
The efficacy of botanicals along with standard fungicides on the incidence of leaf blast was assessed (Table- 1). The pooled mean value of both the years shows significant variation in yield attribute, grain-yield and 100 seed-weights. It was observed that different yield trait responded differently in all the treatments. From the foregoing result it was observed that the botanicals with azadiractin as active ingredients were proved promising however less conspicuous than standard fungicides in reducing disease severity and improving the yield attribute. In the year 2011 the disease index were found in the range of 14.8 to 26.8%.

The suppression in disease severity in the plots sprayed with the botanicals gave promising results. Among the botanicals, Achook was found significantly effective in managing the leaf blast (20.2%) closely followed by Neem Azal T/S (20.4%) and Neem gold. Similarly, in the year 2012 the disease control mechanism using fungicides and botanicals follows the previous year patterns. Though the disease index was comparatively more than previous year, the rate of disease suppressions was statistically effective. A promising disease reduction was observed in plot treated with Achook. The product Neem Azal T/S and Neem gold were found statistically at par with each other against the blast pathogen. The other botanical products also show a better performance in reducing leaf blast severity. It was noticed that the standard fungicide shows maximum suppression of the disease during both the experimental year.