Agriculture Reference
In-Depth Information
1.6 FUTURE TRENDS IN DIAGNOSIS
Since there is no immediate prospect of any exclusive or reliably simple method of
rapidly identifying plant pathogens or the diseases that they cause, most of the diag-
nostic methods currently used in plant disease epidemiology will probably continue
to coexist and be used to some degree in various forms well into the foreseeable
future. It is rather more difficult to decide how extensively methods based on
pathogen biochemistry, microscopy, immunology and nucleic acid similarities will
become established compared with what are now considered the more traditional
methods such as identification by expert visual inspection or microscopic examina-
tion of pathogens
in situ
or
in vitro
as pure cultures (e.g. Cook and Fox, 1992; Fox
and Hart, 1993). Many experienced plant disease epidemiologists can inspect plant
specimens visually for symptoms at the later stages of an epidemic far quicker than
they could carry out most other diagnostic tests. However, for many epidemiological
investigations this is too late and so other more sensitive methods will have to be
adopted either by the investigator or with support from trained experts, as in clinical
diagnosis. These methods will be essential for the more rapid identification of many
types of diseases where current methods are complicated - for example, in those
cases such as the wilts and other diseases where the pathogen is deep-seated in the
tissues, which therefore demands the destruction of the plant. Certain areas are more
likely to benefit than others. The epidemiological studies of soilborne pathogens
would be made easier if the methods were based on biochemical analysis rather than
inspection. Diseased roots traditionally take far longer to inspect than foliage
because the plants have to be dug out or pulled up first, and even then in nearly
every examination there is a delay if a thick covering of soil masks the symptoms
(Dusunceli and Fox, 1992).
Although methods based on nucleic acid can detect the presence of alien
commensals within or on a host, none of the current methods that can be used to
identify an unfamiliar pathogen is without problems. If the epidemiologist lacks
appropriate training and experience, the traditional methods are ineffective without
ready access to accurate disease descriptions that also identify the pathogens in some
detail. At present, even with the major crops, published descriptions can be inadequate
for foreign material. The difficulties are especially daunting on some of the
economically less important and unusual crops - for example, many ornamentals. As it
also takes time to visit libraries and search for reference topics, it seems likely that
this task will be made easier and quicker with the availability of electronic
information systems such as the World Wide Web (www) and as rapid com-
munications with expert consultants becomes cheaper and more feasible through
the Internet. In addition to improved methods of communication for searching the
literature and to satisfy current awareness, when investigating an unfamiliar disease
this information can now be supplemented by data that has been electronically
stored and retrieved from video disks. This system can provide a library of specialist
information on even modest personal computers linked to a CD-ROM (compact-disk
read-only memory) disk player to tap an extensive library of information on the
literature, including illustrations. Eventually, it could become feasible to connect
these with an intelligent scanning system analogous to those used by the police to
