Abstract: Four species of postharvest pathogens from ‘Xiangyan 15’ hot peppers were isolated and identified as Fusarium oxysporum, Colletotrichum nigrum, Colletotrichum gloeosporioides and Rhizopus spp.. The inhibitory effect of alcoholic extracts from nine plants including clove (Syzygium aromaticum), cinnamon (Cinnamomum cassia) and prickly ash (Zanthoxylunm bungeanum) on these pathogens was evaluated by growth rate method. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were measured by plate gradient dilution method. Furthermore, composite guar gum-pullulan coating incorporated with clove and cinnamon extracts was assessed for its ability to induce resistance to Rhizopus spp. in hot peppers by determination of lesion diameter, disease incidence, total phenolic and total flavonoid contents, and the activities of phenylalanine ammonia lyase (PAL), peroxldase (POD) and polyphenol oxidase (PPO). The results showed that all four pathogens were 100% inhibited by clove and cinnamon extracts. Both plant extracts had an equal MIC of 1.25, 2.50, 2.50 and 5.00 mg/mL; and an equal MBC of 2.50, 5.00, 5.00 and 10.00 mg/mL against Fusarium oxysporum, Colletotrichum nigrum, Colletotrichum gloeosporioides, Rhizopus spp., respectively. The disease incidence and lesion diameter in hot peppers caused by Rhizopus spp. were effectively inhibited by the composite coating, which were decreases by 6.67% (P > 0.05) and 30.35% (P < 0.05), respectively after 8 d storage, compared with CK2 (wounded and inoculated with conidial suspension of Rhizopus spp.). Compared with CK1 (wounded and inoculated with sterile water) and CK2, the composite coating enhanced PAL activity by 45.91% and 24.54% (P < 0.05), POD activity by 22.15% (P < 0.05) and 12.54% (P > 0.05), and PPO activity by 80.00% and 28.57% (P < 0.05); and increased total phenolic content by 60.00% and 43.74% (P < 0.05), and total flavonoid content by 82.05% and 61.36% (P < 0.05), respectively. These results suggested that the composite coating containing clove and cinnamon extracts can induce resistance to Rhizopus spp. in hot peppers. Our data provide experimental support for the development of efficient, stable and safe preservatives for hot peppers.

Key words: pathogens, plant extracts, hot pepper, postharvest preservation