New Zealand Journal of Crop and Horticultural Science abstracts

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

KEITH R. SHARROCK

The Horticulture and Food Research
Institute of New Zealand
Ruakura Research Centre
Private Bag 3123
Hamilton, New Zealand

BRIAN T. HAWTHORNE

The Horticulture and Food Research
Institute of New Zealand
Mount Albert Research Centre
Private Bag 92 169
Auckland, New Zealand

JOHN M. YOUNG

Manaaki Whenua--Landcare Research
Mount Albert Research Centre
Private Bag 92 170
Auckland, New Zealand

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 warting 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 Micro-organisms 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.

Keywords  buttercup squash fruit; Cucurbita maxima; warty eruptions; Pseudomonas syringae pv. syringae

New Zealand Journal of Crop and Horticultural Science, 1997, Vol. 25: 203-211

0114-0671/97/2503-0203 $7.00/0 (c) The Royal Society of New Zealand 1997

PDF file of entire paper: medium quality (2493K); (scanned from paper original: notes about this process)

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