Effects of the protective, curative, and eradicative applications of chitosan against Penicillium expansum in apples

Abstract Apple is one of the most important temperate fruit to Brazil economy, and the use of synthetic chemicals has been the main method for reducing postharvest diseases, such as the blue mold, caused by Penicillium expansum. This work intends to evaluate the practical utilization of chitosan for blue mold control. For this purpose, fruits were treated in a preventive and curative way, immersing the fruits in chitosan solution (5 or 10 mg mL-1), or adding a single drop of this solution (10 mg mL-1) directly into the injuries. The eradicative effect of the polysaccharide was also evaluated in vitro and in vivo. Chitosan did not show a curative effect against the blue mold, and its eradicative effect was only evidenced on the higher concentration (10 mg mL-1). On the other hand, preventively, without the addition of adjuvants, chitosan reduced blue mold incidence in fruits by 24% and 93%, through the immersion or the single drop methods, respectively. Thus, it was found that, for long scale utilization, some improvements in the physico-chemical properties of the chitosan are needed, since it was only capable to prevent the infection by P. expansum when directly added on the fruit injury.

Controle do bolor azul em frutos de maçã imersos em solução de ácido salicílico / Control of blue mold on apple fruit immersed in a solution of salicylic acid

O bolor azul, causado por Penicillium expansum, é responsável por grandes perdas nos frutos de maçã armazenados. Buscando medidas alternativas aos tratamentos convencionais, avaliou-se o efeito de ácidos fenólicos (cinâmico, ferúlico, gálico, salicílico e vanílico) sobre Penicillium expansum e sobre a podridão ocasionada nos frutos. Em lâminas de microscopia escavadas, foram avaliados a porcentagem de germinação e o comprimento do tubo germinativo do fungo, empregando-se os fenólicos a 1, 2,5 e 5 mM. In vivo, avaliou-se a intensidade da podridão de Penicillium a partir da imersão dos frutos em soluções fenólicas a 2,5, 5 e 10 mM. Em todos os experimentos, o delineamento utilizado foi o inteiramente casualizado com 4 repetições, sendo a parcela experimental representada por uma gota em lâmina escavada (bioensaios in vitro) ou 4 frutos no interior de uma bandeja plástica (bioensaios in vivo). Dentre os fenólicos, os ácidos cinâmico e salicílico inibiram completamente a germinação do fungo a 2,5 mM, mas somente o ácido salicílico controlou a doença causada por Penicillium expansum quando misturado à suspensão de esporos, reduzindo a incidência do bolor azul em 80%. Desta forma o ácido salicílico apresenta potencial para o tratamento fitossanitário de frutos de maçã em pós-colheita.

The blue mold, caused by Penicillium expansum, is responsible for great losses in stored apple fruit. Searching alternatives measures to conventional treatment, the effect of phenolic acids (cinnamic, ferulic, gallic, vanillic and salicylic acid) on Penicillium expansum and on blue mold intensity were evaluated. In vitro, the percentage of germination and the germ tube length of the fungus were assessed, using the phenolics at 1, 2,5 and 5 mM. In vivo, we evaluated the severity of Penicillium decay in fruits immersed on phenolic solutions at 2,5, 5 and 10 mM. In all experiments, the experimental design was completely randomized with four replications, and the experimental plot was represented by a drop on a microscope slide cavity or by 4 fruits inside a plastic tray. Cinnamic and salicylic acids completely inhibited the germination of the fungus at 2,5 mM, but only salicylic acid controlled the disease caused by Penicillium expansum when it was mixed with a spore suspension, reducing the incidence of blue mold by 80%. Thus salicylic acid has potential to control post-harvest decays.