SEROLOGICAL DETECTION, OCCURRENCE AND SPREAD OF ILARVIRUSES IN TEMPERATE FRUIT CROPS, HOPS AND ROSES IN TASMANIA

Prune dwarf virus (PDV) was commonly found in old declining apricot and cherry orchards, frequently with cherry-like strains of prunus necrotic ringspot virus (PNRSV-G). Trees infected with these two viruses had sparse foliage and in the case of cherries, fruit with a greatly increased incidence of cracking. Trees with one or other virus had intermediate levels of fruit cracking.

PNRSV infections present in stone fruit were not detected with an antiserum to a hop isolate (PNRSV-HP-1) from Washington and antisera to PNRSV-G-like isolates did not detect those present in hop. Isolates from hop were very closely related serologically to apple mosaic virus (ApMV) infections in young apple trees and vice versa.

Spread of PNRSV in hops in the field was often rapid, particularly in cultivars with very abrasive leaves. Plants found infected in the field always occurred clustered together in groups within rows. Similar spread of PNRSV occurred in hop plants grown close together individually in pots. This suggested that most spread of PNRSV in hops occurs through aerial rather than root contact.

Roses in Tasmania displaying bright yellow mosaics and line patterns reacted in ELISA with either ApMV, PNRSV-HP-1 antisera or PNRSV-G-like antisera. Isolates from rose did not infect young apple trees when grafted to them.

Ilarviruses infecting temperate pome and stone fruit and hops are gazetted in Australia as being of quarantine significance and it is therefore vital that appropriate suites of ilarvirus antisera are used when screening material imported from overseas by serology in order to help expedite its release for use by industry.

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