Formulations for delivering Trichoderma spp. spores as seed coatings, effects of temperature and relative humidity on storage stability

Aims: This study aimed to evaluate different formulations for their ability to adhere Trichoderma spores to wheat seeds, and promote survival during storage at a range of temperatures and relative humidities (RH). Methods and Results: We tested a range of formulations, previously used to adhere microorganisms to seeds for their ability to adhere Trichoderma spores to wheat seeds. Treated seeds were stored for six months at a range of temperatures and RH, and formulations were compared for their ability to sustain spore viability. Over the entire experiment there were no consistent significant differences in spore survival among the formulations, but there were significant interactions between the formulations and temperature, RH and time or spore survival. Most notably, under optimum conditions (low temperatures and RH) best spore survival was recorded with a xanthan-gum based formulation. Conversely under suboptimum conditions (high temperatures and RH), survival of spores was best in a waxy-starch formulation, but very poor in the xanthan-gum formulation. Conclusions: These results indicate that Trichoderma spores can be effectively delivered on to seeds and that a xanthan-gum formulation is promising when optimal storage conditions can be maintained. Significance and Impact of Study: Most published formulation papers/patents only report survival of organisms over time at a single or limited number of temperatures, and very few studies have investigated the effects of RH on survival. For the first time, this study shows how different formulations are better suited to certain temperature and RH combinations.