Etiology of almond shriveled kernel disease

In a commercial orchard, mature trees of the almond (Prunus dulcis (Mil.) D . Webb) cultivar 'Butte' propagated on peach (P. persica (L.) Batsch) seedl ings exhibited delayed budbreak in spring, sparse foliage, poor shoot growt h, and produced shriveled kernels. Extracts of leaf petioles from diseased, but not healthy, 'Butte' trees were positive by dot-blot hybridisation ass ays for the presence of a phytoplasma. In addition, diseased almond buds we re graft-inoculated onto the 'Peerless' almond propagated on 'Marianna 2624 ' plum rootstock and induced brown line and pitting at the rootstock/cultiv ar union, a condition associated with peach yellow leaf roll phytoplasma (P YLR-phytoplasma) infection in this indicator host. Furthermore, buds of pea ch infected with PYLR-phytoplasma induced similar canopy and kernel symptom s when bud-inoculated onto previously healthy trees of the almond cultivars 'Peerless' and 'Nonpareil' propagated on peach seedlings. However, a 'Peer less' tree infected with X-disease phytoplasma appeared unaffected. Ilarvir us and dsRNA analyses of diseased 'Butte' trees were negative. Diseased tre es treated with oxytetracycline caused remission of symptoms. These results indicate that infections by a phytoplasma, specifically PYLR-phytoplasma, are responsible for kernel shrivel symptoms in almond trees grown on peach seedlings.