Testing Tree Seeds for Vigor: A Review

Th is review exam ines th e use of vigor tests for tree s e eds . It suggests th at precise evaluations of th e s e tests and th e ir application w ith s eeds of w oody plants is not yet possib le . Th is is due to th e w ide genetic variation, prim arily m anifested in variab le m aturity and dorm ancy, th at exists in m ost tree s e ed lots. Sensitive m easurem ents of germ ination rate during standard germ ination tests h ave proved to b e just as good, if not b e tter, th an any vigor test in judging th e q uality of s e ed lots. Accelerated aging, leach ate conductivity, and germ ination rate all sh ow prom ise, but extensive tests of field em ergence are needed to validate th e lab oratory test procedures and interpretation. INTRO D UCTIO N Th e evo u ion of vigor testing in agricultural seeds has been a slow, arduous, 1 t’ and still unfinished process (McDonald, 1993). Reaching agreement on a definition for “seed vigor” and which tests are suitable for each species, has been difficult. Nevertheless, the efforts of the AOSA Vigor Test Committee and many individuals in the organization bore fruit in the form of a “Seed Vigor Testing Handbook” (AOSA, 1983). This publication was preceded, by two years, by a similar handbook by the International Seed Testing Association (Perry, 1981) that was recently revised (Hampton and TeKrony, 1995). Both handbooks produced a consensus of definitions of seed vigor and both provided recommended and suggested vigor tests that are suitable for many of the major agricultural species of North America and the world. As several individuals were involved in the crafting of both handbooks, there are many similarities in the methods and recommendations. The process still continues, however, as new methods are devised and old ones are improved. Neither of the vigor testing handbooks include recommendations for seeds of trees or of any other woody species. Based on current value of tree seeds alone, this is not surprising, but users of tree seeds (foresters, nursery managers, horticulturists, etc.) perceive a need for vigor testing of tree seeds and have encouraged tree seed researchers to pursue that goal. This review presents the published research on vigor testing of tree seeds, some unpublished data, and suggests which vigor tests show promise for operational use with tree seeds.