Occurrence of White Top of Pea Caused by a New Strain of Pseudomonas syringae pv. pisi.

Abstract

A new bacterial disease has been observed on pea in Shizuoka prefecture, Japan, since 1981. The disease occurs in early autumn when pea plants grow vigorously. The disease is characterized by chlorosis and whitening of apical shoots, including leaflets, stipules, and young pods. Usually, these white top (WT) symptoms are associated with extensive water-soaked lesions on stems and on leaflets at the basal part of the diseased plants. Thirty-four bacterial isolates from WT plants were characterized and identified together with 16 strains of Pseudomonas syringae pv. pisi from common bacterial blight of pea. The bacteria were gram-negative rods, having one to six polar flagella. The results of LOPAT tests were + - - - +, showing that they belong to P. syringe. In stab inoculation on stems, the WT isolates produced WT symptoms with water-soaked spots 14 days after inoculation. The 16 P. syringae pv. pisi strains never induced WT symptoms and, on the contrary, caused the typical bacterial blight. WT isolates were not pathogenic on any other plants tested. Phenotypic properties differentiated WT isolates and P. syringae pv. pisi strains into two groups; one consists of WT isolates and P. syringae pv. pisi group A, the other is P. syringae pv. pisi group B. Two distinct fingerprint profiles were identified by repetitive sequence based-polymerase chain reaction. WT isolates and P. syringae pv. pisi group A belonged to the same fingerprint type in rep-PCR, whereas a distinct fingerprint was shown by strains of the P. syringae pv. pisi group B. We concluded that the WT isolates should be included in P. syringae pv. pisi as a distinct strain in symptom expression.