Optimisation of talcum powder formulation based on Nocardiopsis albirubida strain NA2 spores for biocontrol of Bipolaris sorokiniana root rot in durum wheat seedlings

Abstract

ABSTRACT Bipolaris sorokiniana root-rot of wheat seedlings remains a serious worldwide problem. Spores of Nocardiopsis albirubida strain NA2 were bioformulated as talcum wettable powder (TWP) and clay-alginate pellets (CP) biofungicides before screening for their biocontrol effect. Based on their promising biocontrol results, the talcum powder biofungicide was selected to optimise the bioformulation parameters using the response surface methodology (RSM). The biofungicides TWP and CP significantly (P < 0.05) and respectively reduced the disease severity index (DSI) to 25.6% and 58.2% compared to a positive control (84.0%). Furthermore, the talcum powder biofungicide showed no significant differences compared to a marketed chemical control agent (Difenoconazole®). The TWP biofungicide was selected and a Placket-Burman screening design was explored to evaluate the composition for an optimised biofungicide. Two variables: washed spore density and talcum powder quantity, respectively, showed an important in planta biocontrol effect on B. sorokiniana. The RSM optimisation for the two influencing variables allowed a very notable reduction of the DSI, passing from 25.6% (standard formulation process) to 5.1% (optimised talcum powder biofungicide) by using 25 ml of washed spore suspension (≈107spores ml−1) and 125 g of autoclaved talcum powder. The coefficient of determination R 2 = 0.950 indicated that 95.0% of the response variability can be simulated with the suggested mathematical equation. The spore viability and the biocontrol efficacy have been demonstrated after 12 months storage. The TWP biofungicide based on washed NA2 spores open up promising applications for the biocontrol of B. sorokiniana root rot.