Cluster Rots and Wine Quality Linda F. Bisson Department of Viticulture and Enology University of California, Davis, CA Outline of Presentation u Introduction to Types of Rot u Factors Impacting Rot Incidence u The Fungal Rot Agents u Impact of Rot on Wine Quality Rot Mythology Saccharomyces and other native must yeast flora increase in numbers in rot conditions therefore a little bit of rot gives you a boost in native flora Rot Mythology Saccharomyces and other native must yeast flora increase in numbers in rot conditions therefore a little bit of rot gives you a boost in native flora TRUE, BUT: Spoilage organisms also increase and to much, much higher levels and make it difficult for the good natives to compete Rot Mythology The total number of microbes only increase 10 to 100 fold in damaged clusters Rot Mythology The total number of microbes only increase 10 to 100 fold in damaged clusters TRUE, BUT: The organisms present are completely different genera than the normal native berry flora – Basidiomycetes become ascomycetes – Bacilli become acetic acid bacteria Rot Mythology Disease stress leads to production of desirable grape components because there are more phenolic compounds and more hydrolytic enzymes are present that release bound aroma compounds Rot Mythology Disease stress leads to production of desirable grape components because there are more phenolic compounds and more hydrolytic enzymes are present that release bound aroma compounds TRUE, BUT: Off-characters are also produced, mycotoxins may be formed, aroma of fruit is often suppressed by mold and bacterial metabolites INTRODUCTION TO TYPES OF ROT Types of Cluster Rots u Fungal Invasive Diseases u Fungal (Summer) Sour Rots – “Aerobic” rot u “True” Sour Rots (yeast and bacteria) – “Anaerobic” rot Types of Fungal Attack u Invasive versus opportunistic – Invasives penetrate berry – Opportunists require pre-existing damage u Pre- versus post-harvest rot – Some molds only grow on fruit post-harvest – Some opportunists not found post-harvest »? inhibited by other microbes Fungal Invasive Diseases u Directly invasive of berry tissue – Produce penetrating structures – Produce degradative enzymes – Excrete substances impacting berry surface integrity u Invade plant elsewhere and use vascular system to access berry Impacts of Grape Fungi on Fruit Quality u Enzymatic destruction of berry tissues u Impede ripening u Off-flavor production u Flavor masking u Production of mycotoxins u Stimulation of spoilage bacteria and yeast u Stimulation of phenolic/pathogen responses of plant FACTORS IMPACTING ROT INCIDENCE Factors Impacting Rot Vineyard Environmental ROT Management Conditions Varietal Factors Factors Impacting Rot Vineyard Environmental ROT Management Conditions •Canopy management •Humidity/rainfall •UV exposure •Latitude •Trellis system Varietal Factors •Insect pressure •Soil management •Fungal reservoirs •Insect management •Hail/physical damage •Cluster architecture •Berry/cluster temperatures •Physical/spray damage •Seepage from berry •Cluster drop practices •Bird/animal damage •Varietal composition •Wind •Invasion resistance •Underlying pathology Varietal Factors Impacting Incidence of Rot u Cluster architecture: density and self- imposed damage u Leakiness of berry cells to surface u Skin thickness/ease of penetration u Antifungal response mechanisms u Underlying pathologies: waterberry, berry shrivel, raisining Pre-Veraison Shrivel Damage Tyree Vineyard, UCD “Yellow Berry” Very likely a plastid mutation Tyree Vineyard, UCD Sap on Leaves and Stems Tyree Vineyard, UCD Disease Elsewhere on Vine Fungal attack of stems Tyree Vineyard, UCD Environmental Factors Impacting Rot u Rainfall and relative humidity u Sunlight exposure and berry temperatures u Disease pressure – For entire vine – Presence of reservoirs u Insect presence and damage u Animal presence and damage u Wind Fungal Reservoirs Near Vineyard Powdery mildew on leaves on adjacent foliage – Tyree Vineyard Insect Pressure u Insects that attack or feed on berries u Insects that attack other parts of the plant such as phloem feeders u Insects that are just passing through – Leave sugary secretions behind – Leave microbial hitch-hikers behind “Leaf Bump” Erinose mites (Bud Mites) Tyree Vineyard, UCD Spider Infestations Will impact berry microflora Tyree Vineyard, UCD Secondary Damage to Clusters Caused by Insects Larval feeding resulting in damage to clusters Insect Feeding on Fruit Thrips oviposition punctures Vineyard Practices u Cluster exposure: reduces humidity and “standing water” on berry surface – Leaf removal – Trellis system u Insect management u Soil treatments as many beneficials are soil microbes u Removal of infected plant materials u Control of neighboring reservoirs Spray Damage, Tyree Vineyard, UCD Decayed Clusters Are Reservoirs Mixed Pathologies Possible mite damage, sunburn and/or spray damage and measles Tyree Vineyard, UCD THE FUNGAL ROT AGENTS Pre-Harvest Invasive and Opportunistic Fungi Invasive Opportunistic u Erysiphe necator u Penicillium expansum u Botrytis cinerea u Aspergillus spp. u Guignardia bidwellii u Coniella petrakii u Phaeoacremonium u Rhizopus stolonifer u Alternaria alternata u Trichothecium roseum u Plasmopara viticola Post-Harvest Fungal Infections u Cladosporium herbarum u Mucor spp. u Pre-harvest fungi – Rhizopus – Penicillium Invasive Fungi Causing Rot u Erysiphe necator (powdery mildew) – Can split berry skins u Botrytis cinerea: (noble rot) – Produces antimicrobials – Associated with acetic acid bacteria (sour rot) – Produces laccase – Produces gluconic acid – Under dry conditions infection may be positive under wet conditions get decay of fruit Powdery Mildew Tyree Vineyard Botrytis Rot Photo: UC IPM on line http://www.ipm.ucdavis.edu/PMG/r 302100111.html Invasive Fungi Causing Rot u Guignardia bidwellii: black rot – Brownish red lesions on berry that become black pustules – Leads to drying and mummification of fruit – High rainfall/water demands for growth – Overwinters in mummified clusters – Found in abandoned vineyards u Phaeoacremonium: black measles (esca) Guignarida rot Vidal blanc Esca (Phaeoacremonium) Black measles Tyree Vineyard, UCD Invasive Fungi Causing Rot u Alternaria alternata (Alternaria rot) – Causes berries to leak – Forms a characteristic black smut – Confers a moldy taste to the wine – Requires rainfall late in season and high humidity u Plasmopara viticola (downy mildew) – Can be an agent of immature berry rot, older berries are more resistant Downy mildew Downy mildew Ohio State University Grape downy mildew Midwest Grape Production Guide Plant Pathology, Cornell Bulletin 919-05 http://ohioline.osu.edu/b919/0010.html Invasive Fungi Causing Rot u Phomopsis viticola – Disease of grape vine – Can enter berries via pedicel – Can lead to sour rot Opportunistic Fungi Causing Rot u Require physical damage to fruit – Hail – Insect damage – Bird/animal damage u Require high humidity u Generally found in warmer regions Agents of Opportunistic Sour Rot u Aspergillus spp. (black rot) u Penicillium spp. (green/white rot) u Rhizopus spp. (brown/black rot) u Coniella petrakii (white rot) u Trichothecium roseum (pink rot) Penicillium Sour Rot Penicillium bunch rot: white and green IMPACT OF ROT ON WINE QUALITY Rot and Wine Quality u 5-10%: noticeable reduction in quality u 20-40%: marked reduction in quality u >80%: commercially unaceptable Loinger, C. et al 1977 Am. J. Enol. Vit. 28:196-199 Impact of Rot on Wine Quality u Direct chemical and metabolic effects of mold growth u Effects on plant metabolism and berry composition: plant pathogen response u Encouragement of consortia of spoilage u Indirect effects on yeast fermentation performance Direct Chemical and Metabolic Effects u Moldy taints u Bitterness u Hydrolytic enzymes u Oxidases Effects on plant metabolism and berry composition u Plant response to invasion – Pathogen resistance proteins: cause haze issues – Phenolic array of compounds altered – Peroxide generation systems of plant amplified u Loss of nutrients u Leakage of berry components u Shut-off of plant vascular system to fruit Encouragement of Consortia of Spoilage u Bacteria are responsible for the “sour” in sour rot (acetic acid bacteria bloom, not so much lactics) u Fermentative yeasts bloom (acid tolerant ones, not necessarily the ones you want) Rot Impact on Bacterial Species u Lactic Acid Bacteria – See an increase in Lactobacilli such as Lb. kunkeei and Lb. Lindneri – See slight increases in all lactics that are probably not significant with respect to wine quality u Bacilli and Pseudomonads – See a decrease in the aerobic bacteria that normally colonize plant surfaces Rot Impact on Bacterial Species u Acetic Acid Bacteria – Dramatic increase in numbers »Acetobacter aceti »Acetobacter pasteurianus »Gluconobacter oxydans – Dominate flora of rot u Filamentous Bacteria – Some studies report increases in Streptomyces with rot Rot Impact on Yeast Species u Aerobic (oxidative) basidiomycetes decrease in number u Fermentative ascomycetes bloom – to 106 - 107 cfu/ml – Hanseiaspora uvarum Ethyl acetate producers – Candida krusei – Issatchenkia orientalis – Candida vanderwaltii – Zygoascus hellenicus – Zygosaccharomyces bailii and Z. bisporus Rot Impact on Yeast Species u Select for acid tolerant species u Direct competition with Saccharomyces for nutrients u Saccharomyces has limited acid tolerance Indirect Effects on Yeast Fermentation Performance u Stress imposed by high acid levels u Stress from antimicrobial fungal metabolites: