Seed Today - Q3 2008 - (Page 24)

Seed Vigor Testing Germination vs. Vigor What is high quality seed? ‘Quality’ can be defined as the ability for a seed to establish a seedling under a wide range of environmental conditions. Different types of tests provide components of seed quality information. Purity, germination and vigor tests provide essential data about the quality of a seed lot. There are other important factors such as genetic purity and seed health, but for now, I will focus on vigor testing: its uses and limitations. Standardized germination tests are used to verify the ability of the seed lot to produce a normal plant under optimal conditions. They provide important information on the potential of a seed lot. They allow for comparative tests by buyers, sellers and regulatory agencies. Vigor tests seek to establish how a high germinating seed lot will perform under unfavorable and stressful environmental conditions. While germination is a measurable yes/no quality, vigor involves physiological and biochemical process and their interactions. Vigor is defined by AOSA as “Those seed properties which determine the potential for rapid, uniform emergence, and development of normal seedlings under a wide range of field conditions.” The term “seed properties” is nebulous and indicates the complexity of defining seed vigor. Accelerated Ageing. This is the second most popular test in the United States. It was originally developed to determine the storage potential of seeds. Now, the test is also used to predict field emergence potential. During the AA test seeds are exposed to high temperature and high relative humidity prior to planting. Biochemical Tests. Biochemical tests measure metabolic activity during the early stages of germination. The two most common tests are the conductivity and the tetrazolium (TZ) test. The conductivity test measures the strength of cell membranes. Damaged or weak cell membranes will leak electrolytes. Leakage can be indicative of deterioration or mechanical damage which will affect field performance under adverse conditions. TZ tests distinguish between viable and dead tissues of the embryo. Viable, respirating tissue will stain red when it imbibes tetrazolium. Vigorous, healthy tissue will stain in a consistent and uniform pattern. Seedling growth and evaluation tests. These tests measure phases of seedling growth and development. Emergence counts, seedling growth rate and seedling weight tests are examples of seedling growth rate tests. All vigor tests require laboratory precision and analyst expertise. Minor fluctuations in test environment, especially temperature and moisture, can greatly affect results. Common Vigor Tests Vigor tests seek to measure some factor of seed performance to indicate field potential. No one test has been developed to measure every aspect of seed vigor. This is why understanding the purpose of a vigor test is so important to interpreting its results. The cold test. This is the oldest and most widely used vigor test. It seeks to emulate spring planting conditions by subjecting the seed to cold, moist conditions and seed pathogens in soil. Because pathogen levels in soil will vary, standardization of this test between laboratories has been difficult. Laboratories using one soil type and one cold test method have been shown to provide consistent results. The saturated cold test is a commonly used variable of the cold test in which the soil is kept saturated during the test and corn seeds are planted embryo down. Limitations and Value of Vigor Tests Seed vigor is a relative, not absolute, value. It can be very useful in ranking seed lots and determining relative vigor between seed lots but cannot predict exactly how a seed lot will perform in the field. It takes the investment of time, training and equipment to set up a seed testing vigor program. Seed vigor testing programs cannot be established in seed laboratories overnight. Anita Hall, SCST Executive Director scst@twcny.rr.com / www.seedtechnology.net Dr. Brent Turnipseed, RST, AOSA President brent.turnipseed@sdstate.edu www.aosaseed.com http://www.seedtechnology.net http://www.aosaseed.com

Table of Contents Feed for the Digital Edition of Seed Today - Q3 2008

Seed Today - Q3 2008 Contents Editor’s Notes Cover Feature Fred Miller, Ph.D., MMR Genetics Crosbyton Seed Company AOSCA Greg Lowry Floyd Hansmeirer AOSA/SCST According to ASTA Seedsellers, Inc. BinMaster Blake Sieker Ad Index

Seed Today - Q3 2008

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