Phytormones in kiwifruit plants affected by elephantisis.

Since 2001 an unusual disease, named elephantiasis, was observed in the kiwifruit cultivar ‘Hayward’ in orchards of Northern Italy. The symptom typical of elephantiasis in kiwifruit is trunk hypertrophy, at which a marked brown discoloration of the annual rings is associated. Fungi isolated from necrotic sections of plants are belonging to different fungal genera such as Fusarium spp. - mainly F. solani, Cylindrocarpon spp. and Phialophora-like, that include Phaeoacremonium, Cadophora, Lecythophora. The kiwifruit plant tissue colonization capacity of P. aleophilum, Cadophora melinii and F. solani was verified, while pathogenicity trials using these fungi are in progress in an experimental field. To explain the trunk hypertrophy, trunks of diseased and asymptomatic plants coming from the same orchard were analyzed for the presence of hormones by HPLC-ESi-MS/MS. The hormones analyzed were abscisic acid (ABA), iasmonic acid (JA), salicylic acids (SA), indolacetic acid (IAA) and Gibberellins (GA1, GA3, GA4, GA34). The presence of these hormones showed a similar trend in the majority of the samples either from diseased and asymptomatic plants, except GA34 that it was present exclusively in diseased plants. Gibberellins (GAs) are a large family of hormones that can regulate germination, elongation growth and sex determination. GAs products by fungi are known to induce abnormal tissue growth. These results induce us to further investigate the possible direct production of Gibberellins by the fungi associated to this unusual disease and their involvement in the trunk hypertrophy.