Status of alfalfa witches’ broom phytoplasma disease in Iran

Abstract

Alfalfa witches’ broom (AWB) is one of the most important and destructive diseases of alfalfa in Iran. Based on characteristic disease symptoms and direct and nested polymerase chain reactions, the status of AWB disease was evaluated in different growing areas of Iran. Restriction fragment length polymorphism was used to identify AWB disease associated phytoplasmas. Furthermore, infection rate, disease severity, death rate of infected plant in the summer and winter and overwintering of disease vector were assessed. Based on the results, AWB disease was reported on different alfalfa cultivars in Yazd, Fars, Sistan-Va-Baluchestan, Kerman, Hormozgan, Bushehr, Esfahan, Chaharmahal-Va-Bakthiari, South Khorasan and Khuzestan provinces of Iran. Phytoplasmas associated with AWB in these areas were identified as ‘Candidatus Phytoplasma aurantifolia’, belonging to peanut witches’ broom (16SrII) group. In Abarkooh and Ashkezar (Yazd province) and Bondarooz (Bushehr province) the recorded disease incidence was up to 100%. The highest disease severity was found in Rezvan Shahr (Ashkezar, Yazd province) in 3 years old alfalfa fields. The highest death rate of infected plants in summer and winter were recorded as 26% and 13% in Ashkezar and Abarkooh in Yazd province, respectively. Different nymph stages of the insect vector, Orosius albicinctus, were identified on tamarisk (Tamarix aphylla) and saxaul (Haloxylon persicum and H. aphyllum) in the winter. The highest population of O. albicinctus, observed on tamarisk plants adjacent to the infected alfalfa fields in Milleshbar (Ardakan, Yazd province), suggested this as a possible source of natural spread of AWB.