Effect of Organic Manure in the Induction of Resistance of Citrus to Phytophthora parasitica

Gummosis and root rot caused by Phytophthora are among the most economically important diseases in Citrus. Chemical control has been used; however, it is essential to search for new alternatives for its control. This study aimed to- (i) produce an organic compound from the anaerobic fermentation of cattle manure, (ii) determine the microbial diversity present in the compound, (iii) determine the effect of compound on mycelial growth of Phytophthora parasitica (P. nicotianae), (iv) evaluate its effect in inducing resistance to the pathogen in five Citrus rootstocks and, (v) evaluate the expression profile of some defense-related genes in resistant plants of Poncirus trifoliata and susceptible plants of Caipira sweet orange. The largest microbial population occurred between 25 and 35 days after production of organic manure with predominance of Bacillus spp. The organic manure at concentration of 20% inhibited about 80% of the mycelial growth of P. parasitica. Plants of Caipira sweet orange (susceptible to P. parasitica) when treated with organic manure at all concentrations (10, 20 and 50%), had lower disease severity when compared with the respective control. The analysis of gene expression suggested that the combination of treatment followed by inoculation with the pathogen in plants of Caipira sweet orange, the susceptible genotype, was able to increase the expression level of the genes encoding chitinase (CHI), lipoxygenase (LOX), peroxidase (POX), B-1,3-glucanase and chalcone synthase (CHS). It is believed that they should be involved with the resistance of Citrus plants to P. parasitica.