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ASPARAGUS VIRUS 2: A CONTRIBUTING FACTOR IN ASPARAGUS DECLINE
The yield data from AV2-infected and AV2-free clonal plants were analyzed by ANOVA. AV2 infection caused mean marketable spear yields to be reduced by 14%, 28%, 20%, 48% and 57% and reject yields to be increased by 93%, 105%, 207%, 352% and 167%, during harvest years 1–5 respectively.
Marketable yields from AV2-free plants increased annually over the life of the trial, but marketable yields from AV2-infected plants increased to the third year of harvest and decreased thereafter.
AV2-infected plants produced smaller fern stalks and thinner spears overall.
A second asparagus field trial was established to determine whether spread of AV2 in asparagus crops was caused by movement of AV2-infected sap on knives during spear harvest.
Each row in the trial had two AV2-infected plants in the middle and eight AV2-free plants on either side.
During 1992–1995 spears were hand-harvested, each row in one direction only over the life of the trial.
Spread of AV2 was predominantly in the direction of cutting, with AV2 incidence in plants cut after the AV2 source plants reaching 96% by 1995. In areas cut prior to the AV2 source plants there was some spread of the virus, mainly into female plants and into plants downwind of the source plants, indicating the possibility of wind-assisted pollen transmission.
Similarities between asparagus decline and effects of AV2 infection, in type and timespan of spear and fern symptoms, suggest that AV2 is a contributing factor in decline.
In addition, spread of AV2 on cutting knives may result in increasing numbers of AV2-infected plants, contributing to the overall decline of an asparagus planting.