Almond witches'-broom phytoplasma: a potential threat to almond, peach, and nectarine

A lethal phytoplasma disease of almond, almond witches'-broom (AlmWB), spread rapidly in Lebanon, killing about a hundred thousand trees within 10 years. This phytoplasma was the first member of the pigeon pea group reported to infect stone fruits. Preliminary results of grafting experiments proved that AlmWB could be transmitted by grafting to almond, peach, and nectarine but not to apricot, plum, and cherry. The occurrence of this disease at altitudes ranging from sea level to about 1000 m makes it a major potential threat to almond, nectarine, and peach in the major stone fruit production areas. Using universal primers, nested polymerase chain reaction is normally required for detection; however, the new primers described here allow efficient detection from the first run of polymerase chain reaction.Key words: phytoplasma, almond witche's-broom, almond, stone fruits, Prunus spp., PCR detection.