Residue levels and storage decay control in Cv. Star Ruby grapefruit after dip treatments with azoxystrobin

摘要

Cv. Star Ruby grapefruit (Citrus paradisi Macf.) were subjected to a 3-min dip in water at room temperature (20 degreesC) or at 50 degreesC with or without 25, 50, or 100 mg/L azoxystrobin (AZX). Then, the fruits were subjected to cold quarantine at 2 degreesC and 90-95% relative humidity (RH) for 3 weeks and then stored for 5 weeks at 8 degreesC and similar to85% RH and for another 2 weeks at 20 degreesC and 80% RH to simulate a 2-week marketing period (SMP). No AZX residues were detected in the albedo and pulp following treatments at 20 or 50 degreesC, the total amount of residues being recovered from the flavedo tissue. There was a relationship between the AZX uptake in fruit and the amount of fungicide employed at 20 or 50 degreesC. When AZX was applied to the fruit at 25 mg/L at 20 degreesC, the residue level averaged 0.11 mg/kg (active ingredient, whole fruit basis). This residue concentration increased by 50 and 75% when the application rate increased from 25 to 50 or 100 mg/L, respectively. A similar pattern of accumulation was detected in fruit subjected to treatments at 50 degreesC. However, treatments at 50 degreesC produced residue levels higher than the treatments at 20 degreesC, with increases ranging from 63 to 84%, for the same concentration. Storage conditions did not affect the amount of AZX residues in the fruit. Treatment at 50 or 100 mg/L at 20 degreesC reduced the incidence of moderate to severe chilling injury (Cl). Water dips at 50 degreesC reduced the incidence and severity of Cl to a very low extent, with no additional advantages when hot water was used in combination with AZX. Treatments with 50 or 100 mg/L of AZX at 20 degreesC produced beneficial effects in decay control similar to those of 25 mg/L AZX at 50 OC or hot water alone. Better results were achieved with 50 or 100 AZX at 50 degreesC, providing complete control of decay during cold storage and with negligible decay after SMP. It was concluded that when AZX was applied at 50 degreesC, low doses of fungicide and minimal residue levels in fruit were required to control the postharvest decay of grapefruit. This treatment does not impair fruit quality and offers very interesting prospects for large scale application, due to the reduced potential toxicity of AZX to nontarget organisms and to the environment.