Cantaloupe (Cucumis melo var. reticulatus) is one of the most popular cucurbits grown. Its fruit are shipped all over the world, enabling year-around consumption of this summer vine crop. As with any fleshy fruit or vegetable that is stored more than a few days, cantaloupe fruit are susceptible to many diseases. Many diseases originate from rough handling and improper storage while others begin in the field and develop during storage and transit. Accurate identification of these diseases is important because it will indicate the source of the problem and potential solutions. Accurate identification of postharvest diseases can also lead to proper prioritization of research goals aimed at reducing such losses.
Fruit diseases and postharvest diseases. While all postharvest diseases of cantaloupe are diseases of fruit, most fruit diseases will be culled at harvest. Consequently, postharvest diseases are a subset of fruit diseases; those diseases most likely to escape detection at harvest and become more conspicuous during storage and transit. Granted, some fruit diseases will go undetected at harvest simply because they were poorly graded or inconspicuous. Other fruit diseases will be inconspicuous at harvest and remain so after harvest but will be detected due to increased scrutiny at the point of receipt. This makes it difficult to make clear distinctions between fruit diseases and postharvest diseases. However, it’s important to note that while certain diseases may be common fruit diseases, they may be rare as a postharvest disease. Meanwhile, other diseases increase in importance postharvest because they develop principally during storage and transit and are difficult to detect at harvest.
This important distinction between fruit diseases and postharvest diseases was impossible to address in the key because it does not allow the assignment of probability to each disease (a problem that will hopefully be addressed in future versions of the software). Thus, we have tried to make these distinctions in the fact sheets. This is of great practical important to users of the key. Generally, there will be more than one possible diagnosis after the user has assigned all the attributes s/he can to the disease under investigation. One of the best ways to narrow the choices is to read the “Occurrence & geographic distribution” section of each fact sheet to find out how commonly the disease occurs postharvest.
Key features.
This key is the first of its kind in many respects. “Diagnosing
Postharvest Diseases of Cantaloupe” is the first Lucid key developed
in the U.S. for a set of plant diseases and one of the first plant disease
identification keys ever developed in Lucid. It also is the first published
key to any set of cucurbit diseases.
Another unique feature of this key lies in the content of the Fact Sheets.
Any plant disease diagnostician knows that diagnostic procedures for
specific diseases are either non-existent or difficult to find. Published
disease descriptions typically list symptoms, but the reader is left
to wonder which of the symptoms is particularly diagnostic, which is
common and which is rare. It takes years of experience to become familiar
enough with a set of diseases to be able to put symptoms in the context
of what a reliable diagnosis consists of. Not only is this problem addressed
in the key, but it is also addressed in the Fact Sheet section titled
“Diagnostic methods.” This section is further divided into
methods useful “In the field” and methods appropriate “In
the lab” or diagnostic clinic where more specialized equipment
is available. Many diseases can be accurately identified in the field
because certain symptoms are very diagnostic. Others can be accurately
identified using a handlens and a trained eye to see specific fungal
structures, while others may require overnight incubation to allow development
of fungal structures visible to the naked eye. Relatively few diseases
(e.g., bacterial diseases) require the use of additional diagnostic
methods such as isolation on appropriate media and biochemical assays.
The key is designed for USDA port inspectors, but should be equally
useful to anyone who works with cantaloupe pre- and post-harvest. The
terminology is supported by a glossary
and numerous color photos by the author and T.A. Zitter of Cornell University.
The key covers 24 postharvest diseases using 9 key “features”
and 56 “states” (features and states are Lucid terms for
the characters and subcharacters used for identification). For each
disease there is a corresponding fact sheet, most of which include color
photographs of the disease. Future editions will fill the photo gaps
for diseases and their causal agents. Future editions will also include
common disorders such as sunburn and chilling injury.
There are relatively few texts on diseases of cucurbits and fewer still
that address postharvest diseases of cantaloupe. I have relied on three
texts in particular: Snowdon’s Color Atlas of Post-harvest Diseases
and Disorders of Fruits and Vegetables Vol 2, Blancard at al.’s
Colour Atlas of Cucurbit Diseases and Zitter et al.’s Compendium
of Cucurbit Diseases (see references).
These resources combined with personal experience and that of a few
colleagues (see acknowledgements)
provide the basis for the diagnostic key.
Gerald J. Holmes
North Carolina State University
April 2005
Users of the key
and fact sheets are encouraged to report problems and suggestions to
the author via e-mail: gerald_holmes@ncsu.edu
