Surface Colonization, Penetration, and Lesion Formation on Grapes Inoculated Fresh or After Cold Storage with Single Airborne Conidia ofBotrytis cinerea

Abstract

Infection of grapes by different densities of airborne conidia of Botrytis cinerea was investigated on table grapes (cultivar Dauphine) harvested ripe (16°Brix) and inoculated fresh, or after SO2 treatment and 8-week storage at -0.5°C. Berries were detached at each inoculation and dusted with dry conidia in a settling tower. Following inoculation, the fresh berries were incubated for 24 h at high relative humidity (≥93%), or were overlaid with wet sterile paper towels. Cold-stored berries were incubated at high relative humidity. The effect of conidial density on surface colonization, penetration, and lesion formation was determined by surface sterilization, isolation, and freezing studies on fresh berries. Only symptom expression was determined on cold-stored berries. Fluorescence microscopy of skin segments showed that conidia were consistently deposited as single cells, and not in pairs or groups, on berry surfaces. Individual conidia, at all densities tested, readily infected the cold-stored berries and formed separate lesions after 2 days. Although the cold-stored berries were highly susceptible, lesion numbers were not related to conidial density at low inoculum dosages (0.67 to 2.60 conidia per mm2 berry surface). Lesion numbers tended to increase exponentially at higher dosages (3.24 to 3.88 conidia per mm2 berry surface). Individual conidia, however, did not induce any disease symptoms on fresh berries. Removal of the pathogen after 24-h incubation from the surface of fresh berries by ethanol, and subsequent incubation of excised skin segments revealed that, irrespective of the conidial density or the wetness regime, less than 2% of skin segments were penetrated. Furthermore, increasing densities of conidia did not lead to higher rates of surface colonization and skin penetration. The low incidence of disease caused on fresh berries and high disease incidence induced after prolonged cold storage indicated that infection was not governed by conidial density on berry surfaces, but by the level of host resistance.

Cold Storage and Biocontrol Agents to Extend the Storage Period of ‘BRS Isis’ Seedless Table Grapes

“…High humidity and free water conditions facilitate conidial germination and penetration through cracks or microlesions that can occur during harvest and subsequent handling. These conditions are ideal for infection because fruit tissues after harvest and during cold storage are less reactive due to the weakening of defense mechanisms [32,44]. However, high humidity can be avoided by placing moisture absorption pads at the bottom of the carton boxes.…”

Effect of Fungicide Spray Cover on Botrytis Cinerea Infection in Grape Bunches

“…Dry conidia from a virulent isolate of B. cinerea were prepared as described by Coertze and Holz (1999). Bunches were inoculated with 3 mg dry conidia, which were dispersed by air pressure into the top of an inoculation tower (Plexiglass, 3 × 1 × 1 m [height × depth × width]) according to the method of Salinas et al (1989).…”

“…The conidia were allowed 20 minutes to settle onto the bunches that were positioned on two mesh screens on the floor of the inoculation tower. By using this inoculation technique, approximately three conidia were evenly deposited as single cells on each mm 2 of bunch surface (Coertze & Holz, 1999). Petri dishes with water agar (WA) were placed next to the bunches in the inoculation tower and the percentage germination was determined 6 h after inoculation (100 conidia per Petri dish, two replicates).…”

Gray mold caused by Botrytis cinerea limits grape production in Chile

“…The highest conidial concentrations occur on warm humid days after rain (Diaz, et al, 1998;Leyronas and Nicot, 2013;Mundy et al, 2012;Rodríguez-Rajo et al, 2002Stepalska, and Wolek, 2005). The conidia are produced in multiple and very diverse substrates (Coertze and Holz, 1999;Corbaz, 1972;Holz et al, 2003;Nair and Nadtotchei, 1987;Williamson et al, 2007).…”

“…The nature of physical factors can be biotic (e.g., insects, birds, snails, other plant pathogens) and abiotic (e.g., rain, hail, frost, sunburn, rapid water intake) (Becker and Knoche, 2012a, b;Coertze and Holz, 1999;Fermaud and Le Menn, 1989;Nair, et al, 1988). These factors induce fresh wounds in the skin that are very often microscopic cracks, which prevent the action of the cuticle as a physical barrier to penetration.…”