Control of rice sheath blight by solid and liquid-based spore formulations of a Sri Lankan isolate of Aspergillus niger

Abstract

Sheath blight caused by Rhizoctnia solani Kuhn is a major biotic constraint of rice production worldwide. Our previous investigations have identified Aspergillus niger, a fungus dwelling on the sheath of local rice varieties. as an effective biological control agent in controlling sheath blight in vitro. Moreover, phosphorus solubilization ability of A niger has been reported by previous workers. The present study was conducted to determine the effectiveness of different solid and liquid based formulations of A niger in controlling rice sheath blight together with their effects on increasing phosphorus content in plant tissues and soil. Nine different treatrnents involving three different formulations (i.e. spore suspension, talc-based and straw-based) of the antagonist and the presence or absence of the pathoqen. along with positive and negative controls, were applied on rice (variety BW 361) using a completely randomised design with four replicates. ERASER 5 EC (hexaconazole 50 g/L EC), a recommended fungicide for sheath blight was sprayed on the sheath as one of the treatments at the recommended dosage to compare the effectiveness of the formulations of A niger. Rice plants were established in 5 L pots at five hills per pot. R. solani was inoculated to the soil (one sclerotium/tiller) 45 days after transplanting (OAT). Plants were treated with different treatments three times, namely 60, 68 and 75 OAT. Disease incidence and disease severity (i.e.. % area of lesion development on sheath) were quantified over a period of 32 days after inoculation of R. solani and phosphorus content in rice sheaths and soil was quantified three weeks after the final application of treatments. Treatment effects were highly significant (p<0.0001) on disease incidence and disease severity. According to the findings, out of the three formulations of A niger, the straw-based formulation showed the highest sheath blight control both in terms of disease incidence and severity. All the tested formulations of A niger had similar levels of disease control as the fungicide treatment recommended for controlling sheath blight. Phosphorus content in rice sheath differed significantly (P<O.01) between treatments. Plants treated witn straw-based formulations containing A niger had higher sheath phosphorus contents than plants treated with straw without A niger. The soil phosphorus content did not differ signficantly between treatments. Based on the findings, it can be concluded that the bioloqlcal control agent, A niger, in solid and liquid-based formulations has the potential to replace fungicide applications, either partially or completely, to control rice sheath blight. An additional advantage of A niger was its ability to increase the availability of phosphorus to the plant, when applied as a solid-based formulation with straw.