Association of the Decline of Nashi Pears with an MLO

Abstract

Mycoplasma‐like organisms (MLOs) were constantly detected by the DAPI technique and by restriction fragment length polymorphism (RFLP) analysis of PCR‐amplified DNA in trees of Pyrus pyrifolia cvs Hosui and Kosui grafted on P. communis, seedlings rootstock with symptoms similar to the slow form of pear decline. These symptoms included upward curling of the leaves along the midrib. Leaves were abnormally thick and later turned reddish while major veins became swollen and brown. Trees with symptoms were usually 4–5 years old and were growing in the major pear areas of central Italy. The incidence of affected trees was particularly high in one orchard adjacent to a pear orchard strongly affected with the slow form of pear decline. In this case the distribution pattern of affected Nashi trees suggests that the causal agent was introduced from the adjacent pear orchard by an aerial vector. Although oriental pears are well‐known hosts of the pear‐decline agent when used as rootstocks of French cultivars, this is the first report of pear decline in P. pyrifolia varieties.