Antifungal activity of essential oils in Colletotrichum lindemuthianum and alternative control of bean anthracnose

The major disease of the common bean, anthracnose, is caused by the hemibiotrophic fungus Colletotrichum lindemuthianum and results in significant economic losses. In the present study, we evaluated: (i) the antifungal activity of 26 essential oils (EOs) in the germination and mycelial growth of two isolates of C. lindemuthianum, one of race 65 (LV 136) and the other of race 73 (LV 99), (ii) ultrastructural changes of Cymbopogon citratus, Eugenia caryophyllata and Cymbopogon martini EOs in fungal conidia, (iii) the effect of these EOs on anthracnose control, applied before and after inoculation, and (iv) the effect of C. citratus EOs on the activity of defense enzymes Chitinase (CHI), Polyphenol oxidase (PPO), Guaiacol peroxidase (POX) and Phenylalanine ammonia-lyase (PAL) on bean plants. Of the 26 EOs, 95% of the conidial germination was inhibited by C. citratus, C. martini, Cinnamomum sp., T. vulgaris, E. caryophyllata, and M. recutita at concentrations lower than 0.1%. Mycelial growth was completely inhibited by C. citratus, E. caryophyllata and C. martini at 0.1% for both races. There was little mycelial growth in the fungicide treatment 4 day after infection, DAI. Transmission electron microscopy (TEM) ultrastructure showed that C. citratus, C. martini and E. caryophyllata had direct antifungal action against C. lindemuthianum. These EOs damaged the conidia's ultrastructure by causing vacuolization, cytoplasmic leakage, and plasma membrane invagination. The activity of plant defense enzymes increased in the treatment with C. citratus. Moreover, Cymbopogon citratus and E. caryophyllata decreased anthracnose severity in both the preventive and the curative experiment by 29% and 21%, respectively. Essential oils demonstrated potential for the management of anthracnose in bean crops caused by C. lindemuthianum.