Archivio Journal of Plant Pathology

Abstract:

The seasonal acquisition pattern of Grapevine leafroll-associated virus 1 (GLRaV-1) and Grapevine leafroll-associated virus 3 (GLRaV-3) by the grape mealybug, Pseudococcus maritimus (Erhorn), was determined over two consecutive years in a leafroll-diseased vineyard in the Finger Lakes region of New York. Groups of 1-15 immature mealybugs (1st, 2nd or 3rd instars), adults or eggs were collected from April to November on 20 selected vines infected with GLRaV-1 and/or GLRaV-3. Results of RT-PCR using specific primers were consistent with a preferential virus acquisition by overwintered, 1st instar nymphs in April and May (87%, 45 of 52) followed by summer generation immature mealybugs in July (82%, 28 of 34). Crawlers collected on or near ovisacs in September (100%, 12 of 12) were aviruliferous and eggs collected in June (100%, 250 of 250) as well as crawlers hatching from eggs (100%, 51 of 51) tested negative for the two target viruses in RT-PCR. Importantly, crawlers collected in the vineyard at bud swell in April transmitted GLRaV-1 to healthy grapevines in a greenhouse. These findings suggest that disease management strategies designed to mitigate leafroll spread by reducing vector populations should target overwintered crawlers and second instar crawlers at a very early grapevine development stage, i.e. from bud swell to bloom, as well as the summer generation crawlers later in mid-summer.