Inhibition of in vitro mycelial growth of Sclerotinia sclerotiorum by Brassica juncea ‘Caliente 199’ at different growth stages and plant moisture levels

Abstract

Sclerotinia sclerotiorum causes severe yield losses in horticultural crops worldwide. The use of Brassica spp. as a biofumigant has been shown to have potential to control plant pathogenic fungi including S. sclerotiorum. The Brassica spp. active compounds that exert the inhibitory effect on fungi are isothiocyanates (ITCs) that are released upon the hydrolysis of glucosinolate compounds (GSLs) by the myrosinase enzyme in plant tissues. The accumulation of GSLs in brassica tissues changes with the growth and development of the plants and since ITCs are produced via the hydrolysis of GSLs, moisture level is an important factor for the production of ITCs. The present study investigated the effect of B. juncea (‘Caliente 199’) growth stages under different plant moisture levels, on the inhibition of mycelial growth of S. sclerotiorum. A sandwich plate assay was set up with a Petri plate containing macerated ‘Caliente 199’ tissues sandwiched to a Potato Dextrose Agar inoculated with a mycelial colonised disc of one of four S. sclerotiorum isolates. The treatments included 5 g of macerated fresh whole plant tissues of ‘Caliente 199’ harvested at three different growth stages, vegetative stage, 50% and 100% flowering, adjusted to three different plant moisture levels (80%, 100% and 120% total moisture based on weight). Eight replicates were set up for each treatment combination, including untreated isolate controls, in a randomized complete block design. The S. sclerotiorum colony diameter was measured until the mycelial growth in the controls reached the edge of the Petri plate. The inhibitory efficiency (IE%) of each treatment was calculated by comparing to the mycelial growth in the respective isolate control. There was a significant effect of the flowering stage, moisture content and isolate (P<0.001) on IE% of mycelial growth of S. sclerotiorum. ‘Caliente 199’ at 100% flowering stage showed the highest IE% irrespective of the plant moisture level (94.7%-96.1%). Similarly, 50% flowering stage at 100% plant moisture also had IE% of 94.5%. Further studies will be carried out to test the effect of ‘Caliente 199’ plant growth stages on the viability and subsequent mycelial growth of sclerotia of S. sclerotiorum.