Agriculture Reference
In-Depth Information
10
Seed
Health
Testing
Seedborne pathogens have been recognized as a major means of dissemination of plant pathogens since
prehistoric times. Baker (1972) cites the following historically factual reports of associations between plant
pathogens and seeds.
Claviceps purpurea
on rye (Hellig, 1699).
Orobanche minor
seeds mixed in
Vicia
spp. seeds (Michelli, 1723).
Anguina tritici
in wheat seeds (Needham, 1743).
Dust of bunt balls in wheat was the pathogen
Tilletia
spp. (Tillet, 1755).
Seed pathology, however, did not emerge as a sub-discipline of plant pathology until the early part of
the 20
th
century when seed analysts began to notice relationships between seedborne fungi that developed
during laboratory germination tests and poor seed quality (Neergaard, 1977). These indings initiated a
worldwide process of cataloging seedborne microlora that has recorded associations between approxi-
mately 2400 microorganisms and seeds of 383 genera of plants (Richardson, 1990). Concurrent with these
activities, epidemiological studies were carried out of the seedborne phase of economically important dis-
eases, such as bacterial blights of beans, smuts of cereals, and Stewart's wilt of corn (Neergaard, 1977).
Baker (1972) was the irst to identify these studies with seed pathology. He described three environments
in which seeds exist: the seed production ield; the period covering harvest, conditioning, and storing; and
the planted ield. He also deined categories of associations between pathogens and seeds within the envi-
ronments and indicated how these related to control strategies. McGee (1981) integrated the life cycle of
a plant pathogen into the three environments and suggested that the role of a seed pathologist should be to
study the seed aspects of the life cycle of the pathogen and their interactions with environmental, cultural
and genetic factors that inluence the cycle. The model in Figure 10.1 combines the concepts proposed by
Baker (1972) and McGee (1981) and provides an outline of where various strategies may be deployed in the
management of seed diseases. Seed health testing is an important management practice ensuring seedling
establishment and minimizing transmission of the pathogen to the plants grown from the seeds.
The Application of Seed Health Testing
Seed health testing is primarily applied in management of plant diseases in three ways: to detect inoculum
thresholds of seedborne pathogens that can be transmitted to the plant grown from the seed; to determine
potential impact of seedborne inoculum on stand establishments in the planted ield; and to meet require-
ments for phytosanitary certiication of seed lots going into export markets.
Chapter contributed by Denis McGee, Professor Emeritus Seed Science Center, Iowa State University.
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