REACTION OF STONE FRUIT CULTIVARS TO ALMOND WITCHES' BROOM PHYTOPLASMA *

Almond witches' broom (AlmWB) is an economically important disease in Iran and Lebanon. It is caused by Candidatus Phytoplasma phoenicium, a pigeon pea related (16SrIX) phytoplasma. Graft inoculation was used to study the reaction of stone fruit cultivars  to AlmWB phytoplasma. Two years after inoculation, apricot (cultivars Asefi and Talkh), nectarine (cultivar Red), peach (cultivars Zaferani , Elberta and Shaftalou), plum (cultivars Santa Roza and Shiro), prune (cultivars Sadi and Barghan) and sour cherry (cultivar Schattenmorele) showed  little leaf, internode shortening, leaf rolling, yellowing,  witches' broom and stunting. Incubation period in plants varied from five months in nectarine and peach to nine months in apricot. Growth expression of infected  scions on stone fruit cultivars showed direct relationship with disease severity and inverse relationship with incubation period. Nested-PCR using P1/P7 followed by R16F2n/R16R2 primer pairs confirmed phytoplasmal infection of  all symptomatic  cultivars.   Nested-PCR  also showed that Meshki  cultivar of sweet cherry and Holandi cultivar of prune (asymptomatic cultivars) were infected with  AlmWB phytoplasma. Restriction fragment length polymorphism analysis  of  nested-PCR product (1.2 kbp) using AluI, HinfI and RsaI enzymes showed that phytoplasmas detected in almond and other stone fruits are identical. This is the first report of apricot, cherry, sweet cherry, Shaftalou, plum and prune as experimental hosts of Ca. Phytoplasma phoenicium in Iran. Transmission of this phytoplasma to peach and nectarine was previously  reported.