A study of selected factors affecting efficacy of compost tea against several fungal pathogens of potato

Aim To investigate selected factors of two non-aerated compost teas and mechanisms that influence the restriction of several fungal potato pathogens. Methods and Results Two non-aerated compost teas (NCTs, commercial compost, CCT; vineyard compost, VCT) were tested for their ability to suppress potato pathogens. The VCT was more suppressive than CCT to mycelial growth of A. solani and R. solani isolate 299, but not for R. solani isolate 422. Metagenomic studies of microbial diversity revealed that the CCT had higher fungal and bacterial diversity and richness than the VCT. Use of CCT significantly reduced lesion area of Alternaria alternata on detached leaves, however a gum adjuvant did not lead to significantly greater control. Scanning microscopy showed that the spatial distribution of microbes from the CCT was altered with gum addition, to resemble what may have been a microbial biofilm. Conclusion We confirmed that each NCT could suppress the mycelial growth of selected potato pathogens in culture, and CCT reduced A. alternata lesions on detached leaves. Factors including concentration, microbial communities and physio-chemical properties could not be consistently linked to NCT efficacy. Significance and Impact of the study This study particularly highlights the application of scanning microscopy to study the interaction between pathogens and putative NCT microbes on foliar surfaces. This adds insight to mechanisms of NCT efficacy, along with physico-chemical and microbial characterisation of the teas. This study shows the potential for the use of NCTs as a crop protection tool of low-cost which could be of particular benefit in smallholder agriculture. This article is protected by copyright. All rights reserved.