Parry's disease of pear is the same as pear decline
"Parry's disease", a British disease of pears thought to be indigenous to the UK, has been investigated in order to study possible similarities to pear decline MLO (EPPO A2 organism).
Scientists of Horticulture Research International found mycoplasma like organisms (MLO's) in the tissue of pear cultivars and pear seedlings which were growing under different conditions and which were associated with Parry's disease. Also, an experimental transmission of the MLO's to pear seedlings using Cacopsylla pyricola, vector of pear decline MLO, proved to be successful as well as MLO's were graft transmissible.
The authors suggested, therefore, that "Parry's disease" is caused by pear decline MLO.
Sources
Davies, D.L.; Guise, C.M.; Clark, M.F.; Adams, A.N. (1992) Parry’s disease of pears is similar to pear decline and is associated with mycoplasma-like organisms transmitted by Cacopsylla pyricola.
Plant Pathology 41, 195-203.