Study on the epidemic evolution of leaf spot symptoms caused byP. syringaepv.actinidiaeon kiwifruit

Abstract

The aim of the study was to observe the occurrence and development of the leaf spot symptoms caused by Pseudomonas syringae pv. actinidiae (Psa) on kiwifruit during the growing season in order to determine both the climatic predisposing factors and plant susceptibility. The observation was carried out over the years 2013 and 2014 in naturally infected kiwi fruit orchards. Two kiwi fruit orchards of the ‘Hayward’, and three of the ‘Hayward’, ‘Erika Bo’, ‘Jin Tao’ were observed in 2013 and 2014 respectively. 15-20 shoots of 6 untreated plants were randomly chosen, marked and weekly observed from bud break until leaf fall, scoring the number of new leaves and the number of spots per leaf. In this way it was possible to know the age of the leaf at the onset of the first symptoms and the evolution of the symptoms on the leaves during the season. Weather data were also recorded so as determine the period in which the infection presumably took place. Results showed that, under the climatic conditions of Emilia Romagna, foliar symptoms seem to occur only in springtime and that from the first two weeks of June even newly formed leaves do not show new symptoms of the disease. Finally, the leaves with spots born in spring were randomly collected before their fall and analyzed. From such leaves PSA was always isolated. Therefore, bacterial leaf spots formed in spring remain active until autumn.