Lettuce plants (Lactuca sativa L.) showed definite flowering peaks over a 70-day period. Over 90% of the seed yield was from flowers which opened during the first 35 days, and seed produced from flowers opening during the first 2 flowering peaks were heavier than those produced later in the season. Seed size was not correlated with number of seeds per flower head. Seed yield and quality were not affected by early harvest or by withholding water and nutrients during the last half of the flowering period. Flowering rate, seed yield, and seed quality were not related to air temperature in the range 67 to 94°F.
‘Sumter’ cucumber plants (Cucumis sativus L.) were grown in an acid-washed sand with a modified Hoagland's solution containing calcium (Ca) at 160 (control), 80, or 40 mg·liter−1. Fruits grown under low Ca levels developed water-soaked and necrotic lesions on the epidermis and pericarp of the distal end of the fruits. Some Ca-stressed fruits also developed a placental disruption near the stem-end forming a cylindrical air pocket. Fruit fresh and dry weights from 40 mg Ca/liter were lower than those of the control between weeks 4 to 7 of development. The Ca content of the fruit pericarp sections decreased with increased Ca stress. Regardless of treatment, the proximal peduncle portion contained the highest level of Ca, while the distal section contained the lowest. Seed quality was also reduced from Ca stress. Almost all dry seeds from the control but only 70% of those from 40 mg Ca/liter germinated with the standard germination test. Drying seed at 25C for 5 days reduced the viability of Ca-stressed seeds, when compared to undried seed (72% vs. 99% germination). The vigor of the control seeds was significantly higher when dried. Seeds from the 40 mg Ca/liter treatment produced a significantly higher proportion of abnormal seedlings than the control seeds (58% vs. 4%).
With many seed crops, the most difficult production decision is when to harvest. In indeterminate crops such as Brassica species, early harvests result in immature seed of low vigor while late harvests risk seed deterioration and seed loss due to shattering. To provide a biological basis on which to determine harvest timing, we have characterized seed development in rape seed (Brassica napus L. `Weststar') and red cabbage (Brassica oleracea L. Group Capitata) using population-based hydrotime and ABA-time models. These models provide information relevant to assessing physiological maturity, and therefore, seed quality. The hydrotime and ABA-time models quantify germination rate, the uniformity of germination, viability, and the sensitivity of germination to water potential and ABA. Indices derived from these models, along with maximum germination and t50 values, were used to determine physiological maturity (maximum seed quality) of the seeds during development. The overall trends in seed development were similar in both species: as seeds matured, germination became more uniform and less sensitive to low Ψ and externally applied ABA. The models accurately described germination time courses and final germination percentages except for seeds imbibed at very high concentrations of ABA. In rape seed, physiological maturity was attained several days after maximum seed dry mass, while in red cabbage physiological maturity occurred at or after maximum seed dry mass. Vigor indices were correlated with easily discerned traits such as moisture content and silique phenotypic characteristics. The results of these experiments suggest that hydrotime and ABA-time models can be successfully used to provide a biological basis on which to determine harvest in brassicas.
Seed yield and quality of carrot (Daucus carota var. sativa DC.) were influenced by a wide range of water application regimes and levels. Irrigation treatments were imposed beginning at the time of extension of the primary umbel and extending throughout the reproductive development period. The three application regimes used were: 1) a high-frequency, low water deficit treatment [100% of daily accumulated crop evapotranspiration (ETc)]; 2) a series of five low-frequency (irrigated after 30 mm of accumulated ET,) application treatments with a range of water deficits from moderate to minimal (40% to 120% of ETc applied); and 3) a series of three treatments that had rapidly developing water deficits applied by terminating irrigation at 7, 5, and 2 weeks before harvest after being grown under low-stress conditions. Pure live seed (PLS) yield was optimized by different treatments within each of the three application regimes. Maximum yields were achieved with short-term (2-week) rapidly developing water deficits near harvest, moderate deficit irrigation with 60% to 80% of ETc applied after 30 mm of ETc, or with a low water deficit, high-frequency application. Seed germination percentage decreased as the amount of applied water increased. This effect was more pronounced in the later-developing umbel orders. However, seed quality measured as seedling root length was improved with increasing water application.
Deterioration of snap bean (Phaseolus vulgaris L.) seed quality during accelerated aging at 42°C and 100% relative humidity was accompanied by a decline in germination, radicle emergence, hypocotyl length, and ethylene production. Field emergence of 5 seed lots had a highly significant correlation with ethylene production rates when measured after 22 to 23.5 hours of imbibition at 25°. Seed lots that produced low levels of ethylene emerged poorly in the field. Results indicate that determination of ethylene production of imbibed seeds might be a useful method for detecting changes in seed vigor.
The effect of temperature on seedstalk development, seed yield and quality in carrot (Daucus carota L.) was investigated in growth chambers at constant day/night temperatures of 33/28, 28/23, 25/20, 23/18, 20/15, and 17/12 °C. Days to flowering, seedstalk height, number of umbels, and seed yield decreased linearly with increasing temperature from 17/12 to 33/28 °C. Continuous high temperature (33/28 °C) had a detrimental effect on germination as measured by a standard germination test and an accelerated aging test. Optimum germination of the progeny occurred at 20/15 °C; however, germination rate was faster when seeds matured at 23/18 °C. Seeds that developed at 33/28 °C produced seedlings with the lowest vigor, while those which developed at 20/15 °C produced seedlings with the highest vigor. Brief exposure of plants to 33/28 °C during anthesis or early seed development was as detrimental to seed yield as continuous exposure to 33/28 °C. Exposure to high temperature (33/28 °C) during late seed development had less effect on seed yield, and seed quality was improved. Progeny vigor was reduced greatly by seed development at continuous high temperature (33/28 °C), but was unaffected by brief exposure to 33/28 °C at anthesis, early, or late in seed development. These results suggest that high (33/28 °C) day/night temperatures during pollination, fertilization, or early stages of seed development can greatly reduce carrot seed yield and seed quality.
To understand early development of seed quality, seed lots of sweet corn (Zea mays L.) inbred PGG-27B were harvested from an increase field at 10 stages of maturity, beginning when kernel moisture was at 59% and continuing to 19% kernel moisture content (42 to 103 days after pollination, respectively). Seed lots were dried, hand-shelled, sized, and tested for standard germination and subjected to the seedling growth cold test (SGCT). Endosperm, embryo, and kernel dry weights, and endosperm : embryo (END:EMB) ratios were monitored as the seed matured. Field tests were planted to determine the influence of kernel maturity, grade, and hydration on stand establishment and early seedling growth. Seeds were partially hydrated by mixing with moist vermiculite and screening from the substrate when seeds had reached 30% moisture content. Results from hydrated seeds were compared to those from seeds at ≈10% seed moisture to determine the effect of presowing seed hydration on seedling establishment. The seed hydration effect depended on the environment, but seed size was shown consistently to influence emergence and early seedling dry weight. Seed harvested at 45% to 54% moisture had better stand establishment than seed harvested at the more typical moisture of near 35%. The stage of maturity, determined by kernel moisture, at which PGG-27B was harvested had little effect on standard germination. Hydrating the seed prior to the SGCT improved seedling growth for all early kernel maturities and all seed grades. Embryo dry weight of composite samples increased steadily up to the fifth harvest period (38% seed moisture), then leveled off. Kernel and endosperm dry weights were more variable at the fifth harvest than at others, but followed the same general pattern. The ratio of END:EMB dry weight decreased from the first to the fifth harvest, where it continued at a value near 4.9 through harvest 10. Seed moisture at harvest, seed size, and presowing seed hydration were shown to influence the seed quality of PGG-27B.
Semi-hard seed (SHS) in beans is defined as dry seed which does not imbibe water during a 24 hour soak, but which will gain moisture rapidly at high relative humidity within 14 days and then germinate normally. The inheritance of SHS was found to involve several genes. Soft seed was incompletely dominant to SHS. Narrow sense heritability ranged from 20 to 50% in populations studied. SHS was associated with excellent seed quality resulting in unusually vigorous seedlings.
Flower and fruit production by the columnar cactus, Stenocereus queretaroensis (Weber) Buxbaum, occurred during the dry season in the late winter and spring, and the relatively small annual stem extension occurred primarily during the fall. Thus, reproductive growth does not directly compete with vegetative growth for resources such as reducing sugars, which increased during the wet summer season, a period when total sugars were decreasing. Stem extension, reproductive demography, fruit quality, seed size, and seed quality were not influenced by irrigation. Final fruit size and seed germination, however, were enhanced by applying water. The times from flower bud differentiation to flower opening and from anthesis to fruit ripening were relatively short and unaffected by irrigation.
Endosperm mutants of maize often exhibit poor seed quality, as indicated by poor germination and seedling vigor. The measurement of seed leachate electrolyte conductivity (SLEC) is a rapid method of evaluating seed quality. Generally, high SLEC indicates poor seed quality. Other endosperm types in addition to sugary (su) are becoming important in the sweet corn industry. To facilitate the conversion of inbreds to new endosperm types and maintain acceptable levels of seed quality, it would be useful to determine the relationship between endosperm type and SLEC. The objective of this study was to determine the effects of inbred background, endosperm type, and inbred × endosperm interactions on SLEC and to determine the relationship between seed weight and SLEC. Ten seed weight and SLEC of six near-isogenic lines differing for 10 endosperm types were measured. Ten combinations of the following endosperms were used; sugary (su), waxy (wx), sugary-2 (su2), dull (du), and shrunken-2 (sh2). Significant differences in SLEC were found among endosperm types: sh2 had the highest SLEC (186.1 dS·m−1) and Su su2 the lowest (62.9 dS·m−1). Over endosperm types, 10-seed weight and SLEC were negatively correlated (r = 0.84**). This negative relationship may be due to damage suffered by the pericarp during the collapse of the endosperm of the lighter endosperm types. Significant differences in SLEC also were found among inbreds. Values ranged from 162.3 dS·m−1 to 55.7 dS·m−1. Among inbreds, SLEC and 10-seed weight was positively correlated (r = 0.82*). Endosperm by inbred interactions had significant effects on SLEC. This interaction is of importance to those converting inbreds to different endosperm types and should be considered when choosing seed parents for hybrid production.