Pseudomonas syringae pv. syringae causes wart-like eruptions on fruit of buttercup squash (Cucurbita maxima)

Abstract

Fruit of buttercup squash (Cucurbita maxima D. hybrids ‘Delica’ and ‘Kurijiman') grown at Mangatawhiri, South Auckland, New Zealand, are prone to develop wart-like eruptions during the first 2–3 weeks after harvest. This disfigurement renders the fruit unacceptable for export, and was a serious problem in the 1993–94 season. Isolations from “warts” resulted in the recovery of large numbers of bacteria (>107/g) in the spongy internal tissues. Fungi were infrequently isolated from warts. Bacterial isolates were screened for pathogenicity to pumpkin cotyledons and for the capacity to reproduce symptoms on fruit. Isolates strongly pathogenic to cotyledons and which also induced a typical waiting response were all identified as Pseudomonas syringae pv. syringae on the basis of LOPAT determinative tests, syringomycin production, and pathogenicity to lilac. The same organism was consistently re-isolated from warts produced following artificial inoculation. One re-isolate was tested for wart-inducing capacity, and was found to induce typical symptoms on fruit. Other strains of P. syringae pv. syringae from other cultivars of C. maxima, obtained from the International Collection of Microorganisms from Plants (ICMP), also produced typical symptoms, whereas P. viridiflava, Xanthomonas campestris pv. cucurbitae, and P. syringae pv. syringae from melon and cucumber did not. This is the first report of P. syringae pv. syringae causing significant disease symptoms on fruit of C. maxima. © 1997 Taylor & Francis Group, LLC.