Abstract
Various resistance-inducing chemicals were assessed in the interaction between mango (Mangifera indica L.) and the anthracnose pathogen Colletotrichum gloeosporioides. These were salicylic acid, isonicotinic acid, benzo (1,2,3) thiadiazole-7-carbothionic acid S-methyl ester (Actigard®)7, and other chemical compounds structurally similar, such as nicotinic acid, nicotinic acid adenine dinucleotide, isonicotinic acid ethyl ester, N-oxide isonicotinic acid, benzoic acid and sodium benzoate. No significant differences (P > 0.05) in C. gloeosporioidescolony growth were detected on culture media amended with the different resistance-inducing chemicals evaluated. At laboratory conditions, these compounds were sprayed to runoff on mango leaves and fruit pieces prior to inoculation. Lesion size was significantly reduced (P > 0.10) by concentrations ranging from 10-12 M to 10-6 M of salicylic acid (SA), 10-18 M and 10-14 M of isonicotinic acid (INA), 10-17 M to 10-2 M of Actigard®, and 10-10 M benzoic acid (BA). Salicylic acid, INA and BA caused toxicity on leaves at concentrations ranging from 10-1 to 10-3 M. Chemical compounds that induced resistance at laboratory conditions were further evaluated on six-month-old mango seedlings in a shade house. None of the chemicals tested significantly (P > 0.05) reduced lesion size caused by C. gloeosporioides. Other resistance-inducing chemicals not tested during these studies, such as probenazole, cyclopropane carboxylic acid derivatives, non-protein amino acids [β-aminobutyric acid (BABA) and Ï’-aminobutyric acid (GABA)] and Phytoguard®, should be evaluated individually and in combinations to clarify this lack of induced resistance in mango tissues.