Never-Ending Battle between Defense Metabolites of Indian Oilseed Mustard and the Necrotrophic Fungal Pathogen

Oilseed Brassicas stand first in the edible oil production of India¹ however, are under constant threats from environmental challenges like the white mold disease caused by the necrotrophic phytopathogen Sclerotinia sclerotiorum². Indeed, in case of oilseed mustard Brassica juncea, a dominant oilseed crop of the Indian subcontinent, white mold has become a major limiting factor both during pre and the post-harvest stages with >92% yield losses reported³. Brassica species produce a group of unique defense metabolites called glucosinolates, which along with their hydrolysis products are reported for toxicity against Sclerotinia both under in-vitro and in-vivo conditions^4,5. Nevertheless, pathogens like Sclerotinia, are able to infect, colonize and cause significant yield losses on glucosinolate producing plants. In this context, we initially assessed the disease dynamics of S. sclerotiorum-B. juncea pathosystem at different time points and analyzed changes in the in-planta levels of different glucosinolates (C3, C4 and C5 fractions) during Sclerotinia infection. Our results suggest that, Sclerotinia infection activates the glucosinolate-myrosinase system by modulating changes in total and component glucosinolates of B. juncea plants throughout the time course of infection. We also assessed the toxicity of allyl-ITC (degradation product of sinigrin, an abundant glucosinolate in B. juncea cultivars) on the growth of Sclerotinia in-vitro and observed that this C3-aliphatic glucosinolate derived product, has proven to be one of the most toxic to Sclerotinia. In addition, we performed HPLC analysis to determine the glucosinolate content and types across 250 diverse germplasm accessions of B. juncea that span a range of variation in the glucosinolate metabolite trait, which shall be useful for identification of resistance to Sclerotinia in the mustard crop. Overall, this research work will be useful to understand the disease mechanism and enable selective manipulation of defense metabolites to prevent white mold disease losses in polyploid crop species.

REFERENCES:

1. Jat, R.S., Singh, V.V., Sharma, P. and Rai, P.K., 2019. Oilseed Brassica in India: Demand, supply, policy perspective and future potential. Oilseeds & Fats Crops and Lipids, 26, pp.8.
2. Del Rio, L.E., Bradley, C.A., Henson, R.A., Endres, G.J., Hanson, B.K., McKay, K., Halvorson, M., Porter, P.M., Le Gare, D.G. and Lamey, H.A., 2007. Impact of Sclerotinia stem rot on yield of canola. Plant Disease, 91(2), pp.191-194.
3. Shukla, A.K., 2005. Estimation of yield losses to Indian mustard (Brassica juncea) due to Sclerotinia stem rot. Journal of Phytological Research, 18(2), pp.267-268.
4. Sotelo, T., Lema, M., Soengas, P., Cartea, M.E. and Velasco, P., 2015. In vitro activity of glucosinolates and their degradation products against Brassica-pathogenic bacteria and fungi. Applied and Environmental Microbiology, 81(1), pp.432-440.
5. Stotz, H.U., Sawada, Y., Shimada, Y., Hirai, M.Y., Sasaki, E., Krischke, M., Brown, P.D., Saito, K. and Kamiya, Y., 2011. Role of camalexin, indole glucosinolates, and side chain modification of glucosinolate‐derived isothiocyanates in defense of Arabidopsis against Sclerotinia sclerotiorum. The Plant Journal, 67(1), pp.81-93.