40 WORKSHOP 3 (Abstr. 656) Seed Quality Issues in Medicinal Herbs
Abstract
The sweet corn inbred ‘Luther Hill’ (Zea mays L.) was subjected to soil moisture depletions of −3 and −5 bar either during, 3 weeks after or 6 weeks after silking. The presence of stalk rot (Fusarium moniliforme Sheld.) was significantly increased by increasing soil moisture depletion, particularly when stress occurred at the silking stage. Stress at silking significantly reduced both seed yields and subsequent seed vigor index over all other treatments. Marketable seed and seed size distribution were unaffected by any of the stress treatments.
The shrunken-2 (sh2) mutant of maize (Zea mays L.) increases sucrose and reduces starch in developing endosperm. An associated trait is poor seed and seedling vigor in seeds containing the mutation. The specific effects of sh2 mutant endosperm on embryo and seedling vigor were determined by analyzing seeds that contained either concordant wild-type or nonconcordant combinations of mutant and wild-type embryo and endosperm genotypes. The nonconcordant seed types that contained a wild-type embryo in association with a sh2 mutant endosperm or a sh2 mutant embryo in association with a wild-type endosperm were generated using the TB-3La translocation chromosome in which a wild-type Sh2 gene is attached to the centromeric portion of a B chromosome. Under stress conditions (complex stress vigor test), the seeds with mutant endosperm had lower germination, seedling fresh and dry weight, and index of conductivity than seeds with wild-type endosperm. Mutant endosperm and embryos excised from mutant endosperm imbibed more water than wild-type endosperm or embryos excised from wild-type endosperm. Because of the high concentration of osmotic solutes in the mutant endosperm, a rapid water uptake may induce a membrane disorganization. Leachate conductivities of seeds with mutant endosperm were higher than seeds with wild-type endosperm. In addition, a higher sucrose content and a lower raffinose to sucrose ratio were measured in the wild-type embryos associated with mutant endosperms than in the normal embryos excised from concordant wild-type seeds. These results suggest that a high rate of water uptake caused by the elevated concentration of osmotic solutes in seeds with mutant endosperms may affect membrane integrity during imbibition. Alternatively, the lower raffinose to sucrose ratio present in the mutant endosperm class might affect stabilization of cell membranes during seed desiccation. Embryos cultured in media containing 10% starch or no carbohydrate produced smaller seedlings than embryos cultured in 5% or 10% sucrose. Wild-type embryos excised from mutant endosperms exhibited lower germination in 0% and 5% sucrose media than embryos from concordant seed, indicating that reduced water uptake rates associated with lower external osmotic potential (10% sucrose) can improve vigor of embryos associated with sh2 mutant endosperm. The reduced vigor of embryos and seedlings that develop in association with sh2 mutant endosperm can be traced to the physiological and biochemical effects of the elevated sucrose levels present during seed formation and imbibition.
1 To whom reprint requests should be addressed: Univ. of Arizona, Yuma Agricultural Center, 6425 W. 8th St., Yuma, AZ 85364. Supported by the Western Region Seed Physiology Research Group. The cost of publishing this paper was defrayed in part by
Sweet corn (Zea mays var. rugosa L.) seed with the endosperm mutant shrunken-2 (sh2) often exhibit low seed vigor and poor field emergence. Seed respiration and carbohydrate metabolism during germination of supersweet `Jubilee' (sh2) and sugary sweet `Jubilee' (Sh2) were studied. There were no significant vigor differences expressed by isolated embryos from sh2 and sugary (Sh2) seeds, indicating similar embryo physiology. Respiration rates were higher in the sh2 genotype during early stages of germination (24 hours) while they declined later. The available sucrose originating from the endosperm reserves was depleted by day 4. This insufficiency of a sustained energy source due to rapid consumption and minimal stored reserves may limit subsequent seedling growth in the sh2 genotype.
In plant germplasm conservation, “orthodox” seed (i.e. seed that survives drying down to low moisture content) is the most suitable propagule for long-term storage. In general, high quality seeds of around 5% seed moisture content can be stored for 5-15 years at 2°C and 15-50 years at -18°C. Globally, there are some 1,300 genebanks and 6.1 million accessions of food and industrial crops in conservation. When collecting and conserving plant germplasm, seed science and technology have to be applied during germplasm collection; seed regeneration-germination, seedling establishment, flower synchronization, pollination, harvesting, drying, processing and packaging; seed storage and conservation; characterization and evaluation; and finally, distribution. Some of the seed science knowledge and technology skills encompass seed sampling strategy, sample size, seed health, germination and vigor testing, dormancy breaking, scarification, stratification, vernalization, photoperiod treatment, isolation and pollination techniques, harvesting, threshing, drying, hermetic packaging, storage facility design, etc. The goal is to produce seed lots that fulfill the required genetic, physical, physiological and health quality. A summary was presented to relate germplasm conservation activities to seed science and technology. Some of the seed production, processing and testing equipment used were highlighted. Seed research in germplasm conservation is therefore crucial to streamline the operation and management of a genebank to make it more cost effective and attractive for funding.
78 ORAL SESSION (Abstr. 497-503) CROSS-COMMODITY SEED PHYSIOLOGY I
Poster Session 17–Seed and Stand Establishment 19 July 2005, 12:00–12:45 p.m., Poster Hall–Ballroom E/F
The accelerated aging vigor test subjects seeds to high temperatures (41°C) and relative humidity (about 100%) for short durations (usually 72 hours). These recommendations, however, have been developed for large-seeded agronomic crops and may be too severe for small-seeded flower crops that deteriorate rapidly during storage such as impatiens. We examined the effect of aging regime duration (48, 72, and 96 hours) and temperature (38 and 41°C) as well as relative humidity using three saturated salt solutions (KCl–87% RH, NaCl–76% RH, and NaBr–55% RH) on two commercial impatiens seed lots differing in seed vigor but not percentage germination. The greatest differences in percentage germination after 4 days were found among the treatments of 48 hours for KCl, 72 hours for NaCl, and 96 hours for NaBr. While any of these saturated salt solutions may be used in a commercial situation to determine impatiens seed vigor, we suggest that a total 7-day test period consisting of 72 hours aging at 41°C using saturated NaCl with germination being determined 4 days after aging is most convenient.
Abstract
Phenotypic differences in seed size and protein content were expressed in one cultivar of snap beans by growing them at 2 Michigan locations under 3 N regimes (1969). Each trait was increased by supplemental N applications. Greenhouse studies with ungraded seed of these different phenotypes showed that both seedling size and protein per seedling were positively correlated with seed size and the quantity of protein per seed. When seedlings were grown from small (175 mg) seed and large (275 mg) seed of different protein content there was a correlation between protein content per seed and the size of plants for each size of seed.
Field studies in Central and Northern Michigan (1970) supported the greenhouse findings. Seedling size, yield and number of fruit were more highly correlated with protein per seed than with seed size. When the factor of seed size was eliminated by correlating the percent protein with growth or yield, there were significant correlations for all but one of the field parameters.
Most importantly there was also, with one exception, a significant increase in seedling size, yield and number of fruit from high protein seeds, obtained by supplemental N applications the previous year. These studies provide both correlative, and cause and effect evidence that within a genotype, seedling vigor and yield are related to the protein content or some factor related to protein in snap bean seed.