Potential biofumigation effects of Brassica oleracea var. caulorapa on growth of fungi

Biofumigation, as an environment-friendly alternative to methyl bromide is gaining attention in sustainable agricultural production systems. Based on the biofumigation suppression of growth of three soil-borne filamentous fungi (Fusarium sp., F. oxysporum and P. aphanidermatum), Brassica oleracea var. caulorapa was selected from eight Brassica and other plant species as a potential material for the purpose. Powdered tissues of plants were confined to individual Petri dishes without physical contact with each of the following 28 fungal isolates from 16 hosts: 13 Fusarium spp., two Verticillium dahliae, two Ceratocystis fimbriata, Bipolaris sorokiniana, Gaeumannomyces graminis, Ceratobasidium cornigerum, Rhizotonia cerealis, Phytophthora parasitica, Phytophthora capsici, Botrytis cinerea, two Rhizoctonia solani, Sclerotinia sclerotiorum and Magnaporthe grisea. The level of suppression of growth 7 days after inoculation varied. Based on growth suppression, the 28 isolates were grouped into three clusters by Fuzzy clustering: Cluster I contains F. proliferatum with 20.5% suppression, Cluster II composed of 15 isolates, Fusarium sp., two V. dahliae, two C. fimbriata, B. sorokiniana, C. cornigerum, two R. solani, R. cerealis, S. sclerotiorum, P. parasitica and M. grisea, with 75.2-100% suppression and Cluster III consisted of 12 isolates; five F. oxysporum, F. solani, F. azysporum, F. moniliforme, F. graminearum, F. verticillioides, G. graminis, P. capsici with 40.7-66.2% suppression. Ceratobasidium fimbriata and V. dahliae were more sensitive to biofumigation than S. sclerotiorum and F. culmorum when different amounts of ground powder were used. One gram of powder could suppress the growth of the former two up to 68.6% and 68.7%, but the growth suppression in the latter two by 12.7% and 24.0%, respectively. These results indicated that the amount of plant tissue to be used should be considered depending on target pathogen species. The swollen root of B. oleracea var. botrytis appeared a better material than the leaf for achieving suppression of growth in pathogenic fungi.