Characterizing the Brown Spot Pathosystem in Late-Harvest Table Grapes (Vitis vinifera L.) in the California Central Valley

Abstract

Brown spot, caused by Cladosporium spp., is becoming a problematic postharvest disease of late season table grape (Vitis vinifera) in the California central valley, and management is hindered by knowledge gaps in disease etiology and epidemiology. Brown spot is herein described as a pre- and postharvest dry rot typified by an external brown to black spot or black mycelium which encases the placenta. Isolates in the Cladosporium herbarum and C. cladosporioides species complexes were recovered from 85 and 5% of brown-spot affected berries, respectively. Five isolates in the C. herbarum species complex, representing three phylogenetically distinct species (C. limoniforme, C. ramotenellum, and C. tenellum), and one C. cladosporioides isolate all caused brown spot symptoms under cold-storage conditions, with and without mechanical wounding. Isolate virulence was similar (P > 0.05) based on disease incidence and severity on intact berries but severity varied on wounded berries (P < 0.001). Surface disinfestation reduced severity of cluster rot development following 2 weeks in cold storage (P = 0.027) but incidence was not affected (P = 0.17). This work provides foundational information on brown spot pathosystem etiology and biology in late-harvest table grape, which can be used to improve management.

Inferred microbial networks lack replicability: consequences for next-generation biomonitoring

“…Only two associations were common to all three replicates of the organic system. Both were negative and involved two plant pathogens -Neofusicoccum parvum (Bruez et al, 2014) and Cladosporium ramotenellum (Swett et al, 2016)and two other species known to have antagonistic effects on plant pathogens: Vishniacozyma victoriae and Aureobasidium sp (Pertot et al, 2017;Gramisci et al, 2018). These hypothetical fungus-fungus interactions appear to be relevant but require experimental validation, to demonstrate that networks do contain information about plant health-related mechanisms.…”

Brown spot in table grape Redglobe controlled in study with sulfur dioxide and temperature treatments

“…Brown spot has been attributed to several species of the Cladosporium herbarum species complex (C. ramotenellum, C. tenellum, C. limoniforme) and C. cladosporioides (Crous et al 2007;Swett et al 2016). As described by Swett et al ( fig.…”

“…The cultivar Redglobe is a variety popular for export markets, including China and Mexico, because of its flavor and long shelf life (Dokoozlian et al 1996). Brown spot can cause major postharvest fruit loss in Redglobe and other late-harvest cultivars such as Crimson Seedless and Autumn King (Swett et al 2016). No reliable control of brown spot has been found.…”

“…Redglobe clusters may be stored for 2 to 3 months before they are shipped to Asia. When symptomless berries are in cold storage conditions for long periods, brown spot disease begins to emerge and spread (Swett et al 2016). While initial infections occur…”

“…in the field, once in post-harvest, infection can also easily spread from berry to berry through epidermis contact with no wounding necessary and in temperatures as low as −2°C (Swett et al 2016). Brown spot is a major source of economic loss for grapes during long distance transport.…”