Phylloxera-related Root Damage in Organically and Conventionally Managed Vineyards

Don Lotter, Ph.D.

Dissertation, Graduate Group in Ecology, University of California Davis, 2000

TABLE OF CONTENTS

Chapter One:    The ecology of grape phylloxera and the dynamics of its damage

Chapter Two:    Differences in grape phylloxera-related grapevine root damage in organically and conventionally managed vineyards in California. (Hortscience 34 (6) 1108-1111. 1999) Full text

Chapter Three:   Two pathogen antagonists in organically and conventionally managed vineyard soils and their effects on phylloxera related Fusarium oxysporum infection of grapevine roots.

Chapter Four:    Induced resistance and vineyard soil suppressiveness as soil management dependent factors in reduced fungal rot of phylloxera infested grapevine roots

Chapter Five:    Tests of induced systemic resistance in grapevines

ABSTRACT

Soil-borne fungal pathogen infection of phylloxera infested grapevine roots is an important factor in damage of phylloxera-infested vine roots.  Two years of data collection in phylloxera infested northern California vineyards showed significantly lower fungal pathogen related necrosis in vine roots from organically managed vineyards (OMVs) compared to conventionally managed vineyards (CMVs) (Chapter Two).  Phylloxera populations did not differ between OMVs and CMVs.  Fusarium oxysporum was the most commonly isolated pathogen.

Three areas of disease suppressiveness were tested as possible mechanisms in reducing phylloxera-related vine root necrosis: specific microbial antagonists of pathogens (Chapter 3), general soil suppressiveness (Chapter 4), and induced systemic resistance (ISR) (Chapter 5).

Experiments and a vineyard survey of fluorescent pseudomonad bacteria and a fungus, Trichoderma, both common pathogen antagonists, were done.  Results suggested that the combination of both Trichoderma and pseudomonads tended to decrease (± 0.10) the infectivity of F. oxysporum.  The survey of vineyard soils, both rhizosphere and non-rhizosphere, did not support the hypothesis that pseudomonads are the cause of reduced necrosis in OMVs but did not rule the hypothesis out.

Soil suppressiveness was tested by valuating the ability of vineyard soils’ to suppress F. oxysporum infection of excised grapevine root pieces.  Most of the untreated soils yielded significantly lower necrosis compared to the sterilized control soils.  OMV and CMV soils did not differ in necrosis assays.  Soil percentage organic matter, total nitrogen, and nitrate nitrogen did not explain differences in necrosis.

Induced systemic resistance (ISR) as a cause of reduced necrosis was tested on greenhouse and field grown vines inoculated with F. oxysporum.  Inducing agents BTH, jasmonic acid, F. oxysporum, and phylloxera, plus two induction modifiers, compost and glyphosate, were tested.  BTH treated plants had significantly higher phylloxera reproduction than controls.  Plants subject to the combination of attack by F. oxysporum and compost had significantly lower necrosis than F. oxysporum treatment alone, supporting the hypothesis that compost “primes” ISR.  The salicylic acid and jasmonic acid ISR pathways are discussed in reference to the priming hypothesis and anti-fungal vs. anti-herbivore ISR.