A number of tests, including germination, rate of germination, seedling length, and accelerated aging are being evaluated.

A number of variations of an accelerated aging test were screened. The test is based on the principle that as seeds deteriorate, vigor declines first, followed by loss of viability. By placing seeds in extremely adverse conditions of high temperature and high moisture content, aging equivalent to several years of normal storage can be induced within a few days or even hours. The usefulness of the accelerated aging test is that it can bring out differences among lots which differ little on the standard germination test. Germination after aging should give a better ranking of seed lots for vigor than does germination before aging.

The aging tests generally identified the lowest quality seed lots, but germination after aging was not always correlated with the initial germination percentage. Whether accelerated aging tests can predict field performance still needs to be determined.

Correlation studies were done among various quality characteristics for M-201. All correlations with seedling length were negative, indicating an inverse correlation of seedling length with the other quality characteristics. Testing procedures may have caused this unexpected relationship. Duration of future tests will be shortened.

Field emergence trials need to be evaluated before a firm decision can be made regarding which test, or tests, will give the best indication of potential field performance.

Moisture Effects on Seed Quality Explored

The relationships between seed maturity, seed moisture content at harvest and seed quality are being studied for M-201 and L-202. Seed lots have been harvested at a range of moisture contents and are currently being evaluated to determine 1) whether seed vigor and quality continue to increase as moisture content declines to very low levels, and 2) whether seed maturity or moisture content is the more critical factor for seed quality.

Seed Priming Has Potential for Rice

The idea behind seed priming is to osmotically restrict germination to allow all seeds to reach the same stage, then release the inhibition, giving rapid and uniform germination. Studies have established the ranges of osmotic potentials needed to manipulate rice seed germination. Increasing the osmotic concentration of mannitol in the germination medium successively delayed and prevented germination. Much less osmoticum is needed to delay germination than is needed to completely stop it.

Since rice seed is soaked before planting, these procedures could be incorporated into the soaking period. Another potential application would be to block germination in soaked seeds if bad weather prevents planting on schedule.

 

New Method Tests Seed Vigor One of the keys to profitability in the rice business is starting with quality rice seed. With that in mind, project leader Kent J. Bradford's group tackled three related objectives - to develop a simple yet reliable measure of seed vigor, to determine the influence of seed maturity and moisture in drying and storage, and to investigate methods of improving seed vigor. UC Davis agronomist Kent J. Bradford (r) and postgraduate researcher Michael Ransom examine the variables that determine seed vigor. Standard germination tests exist for investigating rice seed, but what Bradford's research team wanted to develop was a new method that could magnify the differences between seed lots. What they came up with is an "accelerated aging" test that simulates in a few days what rice seed might really experience in the course of several years. Although the results of the aging tests were inconclusive, Bradford, associate professor of vegetable crops at UC Davis, is enthused about the potential applications the technique could have. "Uniformity is critical for management," he said, "especially in regards to herbicides. Weed control could be made easier." Bradford believes the research team has hit upon a fairly simple way of performing the aging test, but the real test will come in the field. "Vigor is a very nebulous term," he said. "The only way to really know is when it's planted in the ground and you see it come up." The researchers initiated studies into the relationship between seed vigor and varying maturity, moisture and storage conditions. Bradford also initiated work into seed priming, a technique in use in some vegetable crops that holds promise for faster, more uniform rice seed germination.