New Zealand Journal of Crop and Horticultural Science abstracts
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
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