Effectiveness of chlorine dioxide as influenced by concentration, pH, and exposure time on spore germination of Botrytis cinerea, Penicillium expansum and Rhizopus stolonifer.

Abstract

Chlorine dioxide (ClO2) is an alternative to hypochlorites (NaOCl, Ca(OCl)2) for fruit and vegetable sanitization to reduce postharvest decays caused, among other fungi, by Botrytis cinerea, Penicillium expansum and Rhizopus stolonifer. Due to economical reasons and because of its explosiveness, the use of chlorine dioxide has been relatively limited. However, the development of stabilized commercial formulations has allowed to reintroduce it. In this study, the efficacy of a new stabilized chlorine dioxide formulation (Tecsa®Clor, Protecsa S.A., Santiago,Chile) to inhibit conidial germination of B. cinerea and P. expansum, and sporangiospore germination of R. stolonifer was demonstrated. The efficacy was dependent primarily on concentration and exposure time but it was also affected by pH. Conidia germination of B. cinerea was inhibited over 98% at concentrations higher than 75 or at 25 mg·mL-1 after 1 or 30 min of contact, respectively. Similarly, over 90% inhibition of conidial germination of P. expansum was achieved with 100 and 25 m·mL-1 after 1 and 30 min, respectively. Sporangiospores of R. stolonifer were inhibited by 90% at 100 mg·mL-1 for 30 min. The pH of the solution increased as chlorine dioxide concentration increased, and the biological activity decreased considerably at pH higher than 8, after 5 and 15 min of contact. No phytotoxic effects were obtained on pear cv. Packham’s Triumph even at 1000 mg·mL-1 after 20-day-exposure at 20 oC. Therefore the stabilized commercial formulation of chlorine dioxide is an alternative to chlorinate water to treat fruits by immersion in order to control B. cinerea, P. expansum and R. stolonifer during postharvest. For a complete control, concentrations higher than 75 mg·mL-1 should be used at pH between 7 and 8. El dioxido de cloro (ClO2) es una alternativa al uso de hipocloritos (NaOCl, Ca(OCl)2) util para la sanitizacion de la fruta en poscosecha y reducir el riesgo de pudriciones causadas entre otros por Botrytis cinerea, Penicillium expansum o Rhizopus stolonifer. Razones economicas y la explosividad de este gas al mantenerlo bajo presion han limitado su uso. Sin embargo, el desarrollo de formulaciones comerciales, estabilizadas, ha permitido reintroducir el dioxido de cloro con estos propositos. En este trabajo se demostro la eficacia de este compuesto, formulado y estabilizado (Tecsa®Clor, Protecsa S.A., Santiago,Chile), en el control de la germinacion de conidias de B. cinerea y P. expansum y esporangiosporas de R. stolonifer. Sin embargo, la efectividad de este producto dependio primeramente de la concentracion y del tiempo de exposicion, pero tambien tuvo importancia en la mortalidad de las esporas el pH de la solucion. Una concentracion de dioxido de cloro > 75 o 25 mg·mL-1 1 o 30 min de exposicion, respectivamente, inhibio en mas de 98% la germinacion de conidias de B. cinerea. En forma similar, se obtuvo sobre un 90% de inhibicion de la germinacion de conidias de P. expansum con 100 y 25 mg·mL-1 por 1 y 30 min, respectivamente. La germinacion de esporangiosporas de R. stolonifer se inhibio por sobre un 90% unicamente con 100 mg·mL-1 por 30 min. El pH de la solucion acuosa de dioxido de cloro aumento considerablemente con la concentracion, disminuyendo la efectividad con pH superior a 8, tanto luego de 5 como 15 min de exposicion. No hubo efectos fitotoxicos en peras cv. Packham’s Triumph aun expuestas a concentracion de 1000 mg·mL-1, luego de 20 dias a 20 oC. Por lo tanto, el dioxido de cloro formulado comercialmente es una alternativa para el control de B. cinerea, P. expansum y R. stolonifer en poscosecha. Sin embargo, se recomienda corregir la dosis en funcion de los patogenos predominantes y verificar el pH de la solucion de modo que esta permanezca entre 7 y 8.