Agriculture Reference
In-Depth Information
Because the standard germination test (SGT) is conducted under optimum conditions, it tends to over-
estimate ield emergence. Seeds may be viable (alive) according to SGT, but so poor in quality that they
may not germinate under ield conditions. Thus, seeds can retain a high germination percentage while
they are in the early stages of deterioration and loss of quality. Therefore, vigor tests were developed to
better evaluate the actual quality of the seeds beyond the ability to produce a normal plant under optimum
conditions.
The definition of Seed Vigor
The deiciencies cited above led to a disquieting recognition for years that not all aspects of seed quality
were being properly identiied by the standard germination test. Initially, it was dificult to agree what these
unmeasured components of seed quality were. Hiltner and Ihssen (1911) used the term
triebkraft
to imply
“driving force” and “shooting strength” of germinating seedlings. In the United States, the early 1930s saw
the acceptance of the term “germination energy” to mean the rate or speed of germination. It was not until
1950, however, that the landmark International Seed Testing Association Congress held in Washington,
DC, focused on these seed quality attributes. ISTA President W. J. Franck, driven by increasing interna-
tional seed trade following World War II, emphasized that international marketing of seeds was dificult
because of discrepancies in germination test results between American and European seed testing labora-
tories. According to Franck, these two regions had differing philosophies about the purpose of a standard
germination test. The Europeans believed that reproducibility of test results was most important to assure
that seed lots could be sold across national boundaries. The Americans believed that the plant-producing
ability of a seed lot was the essential agricultural objective of the germination test. Franck pleaded that
both groups needed to come to grips with these differing philosophies. To stir the debate, he proposed that
germination testing should be conducted under favorable conditions in order that uniform test results be
obtained. The plant -producing ability in the ield of a seed lot was to be deined by a new term: vigor. In
1950, Franck established the ISTA Biochemical and Seedling Vigor Committee and challenged it with two
principal objectives: 1) deine seed vigor, and 2) develop standardized vigor test methods.
The development of a satisfactory deinition of seed vigor has been central to the objectives of both
AOSA and ISTA Vigor Test Committees. Without a deinition, the ability to measure or test this undeined
entity becomes dificult, if not impossible. Fortunately, many deinitions have been proposed. A study of
their evolution portrays the initially confusing and changing status in the expectations for seed vigor. At
the outset, some suggested that seed vigor was so complex that it could not be reasonably deined. They
believed that the notion could only be captured within the framework of a concept. Still others remained
undaunted by the challenge. In 1957, Isely deined seed vigor as “the sum total of all seed attributes which
favor stand establishment under favorable conditions.” Building on this deinition, Delouche and Caldwell
(1960) stated that “seed vigor is the sum of all attributes which favor rapid and uniform stand establish-
ment.” Note the subtle differences from Isely's deinition. Delouche and Caldwell clariied stand estab-
lishment to emphasize rapid and uniform performance, and they also deleted the reference to favorable
conditions. It was clear by this point that rapid and uniform ield emergence were acceptable parameters
of seed vigor. However, the reference to the “...sum total of all seed attributes...” still left unresolved what
the factors were that determined seed vigor. To address this issue, Woodstock, in 1965, proposed that seed
vigor was “that condition of good health and natural robustness in seed which, upon planting, permits
germination to proceed rapidly and to completion under a wide range of environmental conditions. Perry,
in 1973, identiied seed vigor as the “physiological property determined by the genotype and modiied by
the environment which governs the ability of a seed to produce a seedling rapidly in soil and the extent
to which the seed tolerates a range of environmental factors.” He clearly emphasized that seed vigor was
determined by both genetic and environmental components. By this time, consensus was rapidly emerging
on a deinition for seed vigor. In 1977, ISTA formally deined seed vigor as “the sum of all those properties
which determine the potential level of activity and performance of the seed or seed lot during germination
