Abstract
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.
Highlights
Among the problems faced by the Brazilian citriculture, gummosis and root rot caused mainly by Phytophthora parasitica Dastur (= P. nicotianae Breda de Haan var. parasitica (Dastur) Waterhouse) are among the most economically important diseases in Citrus, occurring in most producing regions (Leoni & Ghini, 2006).The oomycete infects the main scaffold branches, leading to canker development and gum exudation, lesion spreads upward, affecting secondary branches, and downward, affecting the trunk and roots (Alvarez et al, 2009)
The results showed that the highest microbial populations was present in organic manure between 25 and 35 days after production, in which it was observed predominance of bacteria and Bacillus and a low total amount of fungi (Figure 1)
It is believed that the total population of microorganisms in organic manure is higher than that indicated from plated samples
Summary
The oomycete infects the main scaffold branches, leading to canker development and gum exudation, lesion spreads upward, affecting secondary branches, and downward, affecting the trunk and roots (Alvarez et al, 2009). Chemicals, such as metalaxyl (a systemic benzenoid fungicide) and fosetyl Al (aluminium ethylhydrogenphosphonate) have been successfully used to control both gummosis and root rot. They are not always desirable due to the high costs of application, potential hazards to the environment, and the development of fungicide-resistant strains. It can provide solutions to both objectives of safe waste management and sustainable agriculture by converting all the societal waste organics into nutritive organic manure which can be used by farmers to grow more food for society (Sinha et al, 2010)
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