Development of a dried Penicillium oxalicum conidial formulation for use as a biological agent against Fusarium wilt of tomato: Selection of optimal additives and storage conditions for maintaining conidial viability

The fungus, Penicillium oxalicum Thom., has been proposed as a biocontrol agent against vascular wilts caused by Verticillium spp. and Fusarium oxysporum. In this paper, we report our findings on the effects of different additives and storage conditions of varying durations, temperatures, and types on the viability and biocontrol efficacy of three different types of P. oxalicum conidial formulations. The viability of the three different P. oxalicum conidial formulations with various solvent stabilizers and moisture contents between <5% and 21% was determined after their preparation and storage with or without vacuum for as long as one year at temperatures that ranged from 4 to 50 °C. The results were compared to those obtained using a dried conidial formulation that was prepared from fresh conidia without any solvent stabilizers. After conducting a series of laboratory assays, and several glasshouse and field experiments over two growing seasons with the different types of conidial formulations, we found that a P. oxalicum conidial formulation with biocontrol efficacy and a long shelf life for controlling Fusarium tomato wilts can be a non-vacuum-packed or vacuum-packed formulation that contains 1.5% sodium alginate, 20% glycerol, 5% sucrose and 5% sorbitol and has <15% moisture content. Although the results on the efficacy of this biocontrol product are promising when the disease pressure of Fusarium wilt is moderate, this P. oxalicum formulation will still need to be improved in order to develop a commercial product that will be efficacious when the disease pressure of Fusarium wilt is high.