PRO/PL> Phytophthora blight, vine crops - USA

[Brian Edmonds]

PHYTOPHTHORA BLIGHT, VINE CROPS - USA
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Date: 23 Apr 2004
From: ProMED-mail <promed at promedmail.org>
Source: Eurek Alert [edited]
<http://www.eurekalert.org/pub_releases/2004-04/aps-dtc042304.php>

Disease threatens cucumbers, pumpkins, and other vine crops
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US plant pathologists are reporting a significant increase in the 
occurrence of Phytophthora blight [Pb] of vine crops, including cucumbers, 
pumpkins, and squash, in many vegetable-growing regions of the United 
States. This devastating disease, caused by the soilborne fungus 
_Phytophthora capsici_ [Pc], often results in nearly total yield loss.

According to Mohammad Babadoost, a plant pathology professor at the 
University of Illinois, Pb has become one of the most serious threats to 
production of vine crops, or cucurbits, in the US and worldwide. Recent 
outbreaks of Pb have threatened pumpkin and other cucurbit industries 
especially in Illinois, which produces about 90 per cent of processing 
pumpkins grown in the US. According to Babadoost, heavy crop losses often 
force growers to abandon their own farms, and move into different areas, 
sometimes traveling more than 50 miles, to find fields free of Pc.

Pb can strike cucurbit plants at any stage of growth. Infection usually 
appears first in low areas of fields where the soil remains wet for longer 
periods of time. The pathogen infects seedlings, vines, leaves, and fruit. 
The disease is usually associated with heavy rainfall, excessive 
irrigation, or poorly drained soil. Frequent irrigation increases disease 
incidence.

Currently, there are no cucurbit cultivars with measurable resistance to 
Pb. Plant pathologists are working to find new methods of controlling the 
disease. Babadoost says that in addition to exploring cultural management 
strategies, plant pathologists are assessing the possibilities of 
biocontrol agents, fungicides for control of the pathogen in cucurbits and 
other crops as well as using induced resistance in plants.

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[A comment is required regarding the phenomenon of induced resistance in 
plants. For example, lower leaves of a plant, when inoculated with a 
necrotizing pathogen, will express typical symptoms in leaves of 
susceptible plants. At a later time (a few days) when newly developed upper 
leaves are inoculated with the same or a related pathogen, fewer lesions 
and/or reduced lesion size are observed, relative to control plants not 
previously inoculated. This phenomenon is described as systemic acquired 
resistance (SAR), and the inducing agent is considered to be salicylic acid 
[SA]. SAR is associated with systemic expression of pathogenesis-related 
proteins (PR proteins) in infected plants. Moreover, application of 
exogenous SA induces both PR proteins and resistance to attack by pathogens.

SAR is a hot topic in plant pathology and plant molecular biology, and I 
have provided a number of references for those who wish to delve further. 
You may also wish to contact Amy Steigman <asteigman at scisoc.org> for more 
information.

Some useful references:
<http://www.apsnet.org/online/feature/cucurbit>
<http://pr-ir2004.risoe.dk/AbstractBook.pdf>
<http://www.aber.ac.uk/plantpathol/sar.html>
- Mod.DH]

[see also:
2003
---
Phytophthora capsici, tomato - South Africa       20031130.2971
Phytophthora capsici, tomato - Mexico (Michoacan) 20030711.1708
2002
---
Phytophthora capsici, cucurbits - Spain (Granada) 20020608.4440]

.....................mpp/dh/pg/sh

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