Occurrence of Apical Shoot Chlorosis and Whitening of Pea Caused by Strains 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 characterised by chlorosis and whitening of apical shoot including leaflets, stipules and young pods. Usually, the Apical Shoot Chlorosis and Whitening (ASCW) symptoms are associated with extensive water soaking lesions on stems and on leaflets at the basal part of the diseased plants. The latter are the common symptoms of bacterial blight caused by Pseudomonas syringae pv. pisi. Fifty-one bacterial isolates, including 35 strains from ASCW and 16 from common bacterial blight of pea, were characterised and identified as P. s. pv. pisi. The bacteria were Gram-negative rods, having 1 to 3 polar flagella. The results of LOPAT tests were + − − − +, showing that they belong to P. syringae. In stab inoculation, the isolates from ASCW reproduced ASCW symptoms with water soaking spots 14 days after inoculation. P. s. pv. pisi strains never induced ASCW symptoms and, on the contrary, caused the typical bacterial blight ones. ASCW strains were not pathogenic on any other plants tested. P. s. pv. pisi strains were divided into 2 groups (A and B) according to their phenotypic properties. These were identical among ASCW strains and P. s. pv. pisi group A. Two distinct fingerprint profiles were identified by rep-PCR. ASCW strains and P. s. pv. pisi group A belonged to the same fingerprint type in rep-PCR, whereas a distinct fingerprint was shown by strains of the P. s. pv. pisi group B. We concluded that the ASCW strains should be included in P. s. pv. pisi as a distinct variant group distinguishable for symptom expression.