IDENTIFICATION AND PATHOGENICITY OF PSEUDOMONAS SYRINGAE GENOMOSPECIES 1 PHYLOGROUP 2B CAUSING LEAF SPOTS AND FRUIT WARTS ON CUCURBITS IN WESTERN WASHINGTON, U.S.

Abstract

Pseudomonas syringae pv. lachrymans and pv. syringae have been identified as pathogenic on cucurbit crops in the United States and based on molecular data, pv. syringae (genomospecies 1) are genetically distinct from pv. lachrymans (genomospecies 2). In 2015, leaf lesions, and bull’s-eye lesions and raised warts on fruit were observed on ‘Cinnamon Girl’ pumpkins near Mount Vernon in western WA. PsAs_2015 was collected from leaf lesions and PsFt1_2015 and PsFt2_2015 were collected from fruit. The isolates were phenotypically and molecularly characterized. LOPAT results were consistent for P. syringae. Neighbor joining and Bayesian analyses of gltA and gyrB sequences clustered the three isolates within genomospecies 1 phylogroup 2b. ‘Cinnamon Girl’ seedlings inoculated with these isolates were spotted with small lesions having chlorotic borders. Seedlings and fruits of 11 pumpkin and squash cultivars were inoculated with PsAs_2015. Altogether, 100% disease incidence occurred on five cultivars 2 (Baby Bear, Baby Boo, Cinnamon Girl, Lil’ Pump Ke Mon, Spaghetti) of seedlings and six cultivars (Cinnamon Girl, Jack Be Little, Lil’ Pump Ke Mon, Honeyboat, Spaghetti, Sweet Dumpling) of fruit. gyrB sequence data of isolates recovered after inoculation were comparable to PsAs_2015 on 33 to 100% of seedlings and fruit. The clustering of PsAs_2015, PsFt1_2015, and PsFt2_2015 with other genomospecies 1 pathovars confirms that they are distinct from P. syringae pv. lachrymans and represents a first report for Washington State. Moreover, the presence of wart symptoms on pumpkin fruit represents a newly observed symptom in the United States.