Use of phosphites in postharvest to control anthracnose of yellow passionfruit

Abstract

Brazil is the largest producer of yellow passionfruit (Passiflora edulis f. flavicarpa) and one of its production problems is the anthracnose (Colletotrichum spp.). The use of fungicides on control of postharvest diseases is a method that protects the fruits during storage. However, precautions must be taken due to fungicide toxicity. The restriction to the use of fungicides in post-harvest led a demand for alternative methods of disease control, and, the phosphite application is one of these methods. Therefore, this work aimed to evaluate the effects of fruit immersion in phosphite on postharvest control of anthracnose. Two tests were developed in vitro to assess the effect on the fungus: phosphite Mg2 (40%P₂O₅+6%Mg), Zn (40%P₂O₅+10%Zn), Ca1 (30%P₂O₅+7%Ca) and K1 (40%P₂O₅+20%K₂O). For the in vivo tests, passionfruit (Gigante Amarelo), were wounded and inoculated (50mL; 10⁶conidia mL^-1). Two tests were done with: Cu (25%P₂O₅+5%Cu), 2.5mL L^-1; Zn, 2.5mL L^-1; K1, 2.5mL L^-1; Mg1 (30%P₂O₅+4%Mg), 3mL L^-1; Ca1, 3mL L^-1; Ca2 (10%P₂O₅+6%Ca), 4mL L^-1; K2 (40%P₂O₅+20%K₂O), 1.5mL L^-1; Mg2 (40%P₂O₅+6%Mg), 1.5mL L^-1; K3 (20%P₂O₅+20%K₂O) 1.75 mL L^-1; K4 (30%P₂O₅+20%K₂O), 1.75mL L^-1. Other two tests with phosphites Mg2, Ca1, Zn and K1 were with CaCl₂ (2%) was developed. In addition, phosphites were tested at 25, 50, 100 and 200% of the dose: K2 (100%; 1.5mL L^-1) and Ca1 (100%; 3 mL L^-1). The phosphites Mg2, Ca1, K1 and Zn in vitro have reduced mycelial growth and fungus conidia production. The phosphites K1, K2, Ca1 and Zn were the ones that most reduced the size of the anthracnose lesion. There were no differences among treatments, concerning the physico-chemical fruit properties analyzed (% fresh mass loss, total soluble solids, pH and titratable acidity).