Isolation and characterization of extracellular polysaccharide from Colletotrichum gloeosporioides: New plant immune elicitor for plant protection.

Searching for natural products from microbial sources is an important approach in the development of green pesticides. Here, we isolated a homogenous extracellular polysaccharide CPEPS-2 from Colletotrichum gloeosporioides PHXP3 by bioassay-guided strategy. Chemical and spectroscopic analysis showed that CPEPS-2 consisted of glucose, mannose and galactose in percentages of 38.98:40.04:20.98 and its molecular weight was estimated to be 23.8 kDa. The backbone of CPEPS-2 was consisted of →2)-α-D-Manp-(1→, →6)-α-D-Manp-(1→, →4)-α-D-Glcp-(1→, →2,6)-α-D-Manp-(1→ and →4,6)-α-D-Glcp-(1→ residues, and the branches consisted of ß-D-Galf-(1→ unit. In bioactive assays, CPEPS-2 effectively induced systemic resistance of tobacco and soybean against Phytophthora capsici and P. sojae at 100 µg/mL, with inhibition rates of 60.1 % and 68.8 %, respectively. Furthermore, in greenhouse tests, 100 µg/mL CPEPS-2 displayed potent activity against P. capsici and P. sojae with protection efficacies of 75.0 % and 80.4 %. Simultaneously, CPEPS-2 promoted PR1 expression and callose accumulation in Nicotiana benthamiana. In addition, subcellular localization indicated CPEPS-2 was localized to the cell membrane or the wall of plant cells. The results suggested CPEPS-2 could act as a carbohydrate elicitor to induce plant immunity.