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.
Several soilborne diseases severely affect eggplants (Solanum melongena L.) in Japan. Therefore, eggplants are usually grafted on rootstocks of various species resistant to these diseases. For the control of verticillium wilt (Verticillium dahliae Klebahn), Solanum torvum `Torvum vigor' plants are used for rootstocks. However since the seeds started to emerge after 12 - 14 days at 25C and only 40% of them emerged after 30 days, it was difficult to obtain seedlings of uniform size.
In this experiment, matric priming treatment of seeds prior to planting was modified to improve the emergence of the seeds of `Torvum vigor'. Vermiculite powder was selected as the substrate to control the water potential of seeds during the treatment. First, samples of 0.25g seeds (235seeds on an average) were mixed with various amounts of vermiculite powder and water at 25C in the dark during 1 week. Thereafter, the treated seeds were planted in soil and incubated at 25C under a 12h daylength regime and the emergence and growth were monitored. Second, the temperature for the treatment, growth regulators added to water, air pressure and components, and the duration of the treatment were varied. Finally, the optimum treatment for improving the emergence of Solanum torvum seeds was developed.
In developing countries, the use of True Potato Seed (TPS) technology offers some potential economic and biological advantages compared to using seed tubers. One problem with using TPS technology is the lack of seedling vigor, poor germination and non-uniformity of seedlings derived from TPS. Open-pollinated true seeds were divided into three classes based on differences in embryo morphology. Highly significant differences were observed among these seed classes for 100-seed weights, percent germination, rate of germination, 10-seedling weights and percent seedlings with leaves unfurled, ten days after sowing. Seed classes were quantified in terms of 100-seed weight with Seed class 1 having the lowest weight and Seed class 3 the highest; A significantly high r value (0.99) was obtained between seed classes and 10-seedling weight. High r values (0.93) and (0.94) were also obtained between seed classes and percent germination and percent seedlings with unfurled leaves, respectively. Results indicate that it may be possible to use these differences on embryo morphology as a basis for selecting vigorous true potato seeds.
The effect of fruit age (30 to 50 days after anthesis), fruit storage (seed extracted 0 to 20 days after harvest), and seed storage (0 to 12 months) on seed weight, emergence and vigor were studied in two tropical populations of pumpkin (Cucurbita moschata). In separate experiments fermentation of extracted seed was studied using several tropical and temperate genotypes. Emergence reached nearly 100% in seeds from fruit harvested 45 days after flowering, no matter how many days these fruits were stored. Seed weight and emergence markedly increased for seed extracted from less mature fruit (harvested 30 to 45 days after anthesis) when those fruits were stored for 15 to 20 days after harvest. Emergence improved during the first 3 months of seed storage, then leveled off during the remainder of the study. Fermentation of the seed and placental material for 48 hrs followering extraction does not damage seed. The seed extraction process is simplified and the emergence rate appears to increase possibly due to faster imbibition in fermented seed.
Sweet corn with the shrunken-2 (sh2) gene is characterized by poor seed emergence and low seedling vigor. Also, this variety is sensitive to flooded conditions. Our objective was to determine the effects of aeration, during priming treatment, on germination and vigor. Priming consisted of aerating sh2 maize seed during soaking then drying on a lab bench overnight under a fan. Fifty seeds at a time were soaked (25 ± 2C) in 100 ml deionized water. During this time they received either 75% O2: 25% N2, pure N2, pure CO2, or no gas (soak control) for up to 6 hours. The flow rates ranged from 0.35 to 2 standard liters per minute for 75% O2: 25% N2, 0.8 to 2.5 for N2, and 0.5 to 1.3 for CO2. Pressure was held constant at 1 psi. All samples were weighed before soaking, immediately after soaking, and again upon partial drying. Germination was counted after 7 days using the rolled paper towel method (25 ± 1C). Radicle lengths were measured after 72 hours. Oxygen (75%) increased vigor. Also, O2 permitted greater water absorption (P < 0.02). Carbon dioxide and N2 both decreased vigor. Data suggest that aeration conditions (75% O2) during the hydration treatment has beneficial effects.
A rapid and reliable predictor of sweet corn seed field emergence is required to produce high-quality, uniform crops. Field emergence of seven sh2 sweet corn cultivars grown at 3 geographic locations in Florida over 2 planting periods (fall and spring) was correlated with laboratory vigor tests. Factor analysis was used to separate non-collinear vigor tests for subsequent multiple regression models. The best single predictor test (R2=0.93***) was an index based on conductivity of the leachate and germination percentage after complex stressing vigor test incubated at 15°C. Leakage conductivity after 3 h soaking at 25 or 30°C (R2=0.90***), cold test in soil (R2=0.90***), mean alternate temperature stress conductivity test (R2=0.88***), standard germination test incubated at 30°C (R2=0.88***), and the index incubated at 25°C (R2=0.88***) were also good predictors of field emergence. Non-collinear tests including the towel germination test at 25°C and an alternate temperature stress conductivity test generated the highest most significant two factor predictor (R2=0.89***), and with glutamic acid decarboxylase activity (GADA) the best three factor predictor (r2=0.93***). The index of conductivity and complex stressing vigor test (ICS) proposed as a predictor of seed emergence considered two main factors affecting emergence in sh2 sweet corn: the condition of the membrane of the seeds and potential pathogen infection.