Outbreaks of Cladosporium Rot Associated with Delayed Harvest Wine Grapes in Chile.

Abstract

Severe outbreaks of Cladosporium rot have occurred on berries in clusters of late harvest wine grapes (Vitis vinifera L.) during the 2003 to 2006 growing seasons. This disease was especially prevalent on Cabernet Sauvignon (CS) vineyards in central Chile where disease incidence commonly comprised 50 to 100% of the clusters at harvest. Symptoms appeared on mature grapes (total soluble solids [TSS] >22%) and were characterized by berry dehydration, a firm decay affecting a small portion of the berry and a superficial olive-green mold. Isolations made on acidified potato dextrose agar (APDA) consistently yielded olive-green colonies after 7 days at 20°C. On the basis of colony morphology and morphological characteristics of conidiophores and conidia, Cladosporium herbarum (Pers.:Fr) Link and C. cladosporioides (Fres.) de Vries were identified (1). These species were primarily separated by the presence of rough and smooth conidial surfaces, respectively. Koch's postulates were completed by inoculating 80 wounded mature (20% TSS) CS berries and incubating them at 10, 20, and 30°C. An equal number of wounded but noninoculated berries were left as controls. Berries were surface sterilized (75% ethanol for 30 s and 0.5% sodium hypochlorite for 60 s), inoculated with 10 μl of a 106 conidial suspension per ml applied to the wounds made with a sterile hypodermic needle. Dark, necrotic lesions, 1 to 6 mm in diameter, and a dark mycelial colony appeared on the surface after 7 days in chambers with relative humidity of >95%. Disease incidence was significantly (P < 0.05) influenced by temperature, with 90, 100, and 49% of inoculated berries becoming infected when incubated at 10, 20, or 30°C, respectively. C. herbarum and C. cladosporioides appeared to be equally pathogenic, producing symptoms similar to naturally infected CS berries, and were reisolated (100%) on APDA. These same isolates were pathogenic when tested on mature (TSS >16%) Thompson Seedless (TS) berries. Fungicide sensitivity tests were performed on detached TS berries challenged by placing 10 μl of a 106 conidial suspension per ml of C. herbarum on injured berries. Boscalid (0.5 mg/ml, Cantus WG; BASF, Santiago, Chile), iprodione (0.5 mg/ml, Rovral WP; Bayer Crop Science, Santiago, Chile), pyraclostrobin (0.085 mg/ml, Comet SC; BASF), and pyraclostrobin (0.009 mg/ml) mixed with boscalid at 0.017 mg/ml (Bellis WG; BASF) provided a significant control (P < 0.05) with efficacy between 84.3 and 95.9%. Azoxystrobin (0.188 mg/ml, Quadris SC; Syngenta Crop Protection, Santiago, Chile), kresoxim methyl (0.067 mg/ml, Stroby SC; BASF), and trifloxystrobin (0.06 mg/ml, Flint WG; Bayer Crop Science) provided partial control with efficacy between 23.1 and 42.1%. Cladosporium spp. have been previously reported (2). However, severe outbreaks of Cladosporium rot occur when berries become partially senescent because of a considerable delay in harvest (3). This appears to favor the development of these pathogens.