Seed set is affected by many factors. One of the most important is the number of pollen grains that germinate on the stigma. Our research has shown that kaempferol (a plant natural product) is required for pollen germination. Pollen lacking kaempferol does not germinate, but this defect can be reversed by adding powdered kaempferol to the stigma at pollination. Within 24 hours of wounding the corolla or stamens of V26, a Petunia inbred, high levels of kaempferol accumulate in the stigma. The requirement for kaempferol in pollen germination, and the high levels that can accumulate in the stigma, suggested that seed set might be enhanced by wounding 24 hours before pollination. We tested this hypothesis in two inbred lines of Petunia, a Petunia outcross, and another solanaceous plant Nicotiana tobacum cv. Samsum. The number of seeds per capsule were correlated with the levels of kaempferol in the stigma in wounded and non-wounded flowers.
Ellen K. Muchmor and Loverine P. Taylor
Ricard D. Lardizabal and Paul G. Thompson
Four sweet potato [Ipomoea batatas (L.) Lam.] cultivars responded differently to growth regulator application for number of flowers produced, percentage capsule set, and number of seeds produced. Gibberellic acid, 2,4-D, and BA application resulted in the highest number of flowers by `Jewel', `Shore Gold', and `Vardaman) plants, respectively. Application of GA3 to `Jewel', 2,4-D or ethephon to `Shore Gold', and BA to `Vardaman' produced the highest number of seeds. Grafting to rootstock of Z. carnea Jacq. spp. fistulosa (Mart. ex Choisy) D. Austin increased flower numbers, percentage capsule set, and number of seeds in all cultivars. The effects of growth regulators and grafting were additive for flower numbers, percentage capsule set, and number of seeds. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (BA), (2,4-dichlorophenoxy) acetic acid (2,4-D), (2-chloroethyl) phosphoric acid (ethephon), and (1α, 2β, 4a α, 4b β, 10)-2,4a,7-trihydroxy-1-methy1-8-methylenegibb-3-ene-1,10-dicarboxylic acid 1,4a-Iactone (gibberellic acid; GA3).
Ayman F. Abou-Hadid, Abo-Elfotouh M. Abd-Alla, and Richard A. Jones
Cucumber plants )Cucumis sativa cv. Beta-al-pha) were grown in a glasshouse in pots of sand with 3 NaCl levels in the nutrient solution (0.40 and 60 mM) and placed in four large water baths controlled at different temperatures (13, 18,23, and 28°C). The increase of NaCl levels decreased the vegetative growth, seed yield, and seed quality, while the increase of root zone temperature up to 23C° increased the vegetative growth, seed yield and quality. Whereas, 28°C showed lower effect than 23°C. Ethylene production and the content of proline and free amino acids were increased with increasing NaCl levels. The increase of root zone temperature till 23°C decreased ethylene production, proline, and free amino acids contents. Zero NaCl (as control) obtained with 23°C root zone temperature appeared to be the best for the over-all growth, seed yield and seed quality of cucumber plants.
M. Aneja, T.J. Gianfagna, S.A. Garrison, and E.F. Durner
Precocious flowering can be induced in asparagus (Asparagus officinalis L.) seedlings with N-phenylcarbamate herbicides, such as n-propyl N-(3,4-dichlorophenyl) carbamate (NPC); however, only ≈50% of the treated seeds produce flowering plants because these compounds inhibit germination and seedling emergence. We have improved the treatment method by determining the environmental conditions, timing, dose, and duration needed to maximize the percentage of germination, emergence, and flowering. Imbibing seeds in water for 5 days, and then treating germinated seeds with 0.4 mm NPC for 5 days after radicle emergence, with seedling aeration in the light, resulted in the production of flowering seedlings from >90% of the treated seeds. For freshly harvested seeds, in which germination rates are more variable than aged seeds, individual seedlings must be transferred to NPC within 1 day after radicle emergence to produce a high percentage of flowering plants. For seven male asparagus cultivars, chemical induction of flowering in seedlings with NPC produced a sex ratio similar to that of field-grown plants, demonstrating that NPC induces flowering without altering floral differentiation or sex expression. This method can be used for rapidly and accurately identifying the percentage of females in “male” cultivars.
Claudio R. Galmarini
Haim D. Rabinowitch, Batya Friedlander, and Ross Peters
Recently, a dwarf scape mutant was found in `Autumn Beit-Alpha' onion (Allium cepa L.). The development of dwarf scape in onion, the genetic control of this attribute, and its response to external application of ethephon and GA3 were studied. Data from segregating populations conclusively showed that a single recessive gene, designated dw1, controls scape dwarfness in onions. Its expression is slightly modified by minor genes. Relatively slow growth and early cessation of cell elongation are the characteristics associated with scape dwarfness. A similar developmental pattern characterized emerging normal flower stalks treated with ethephon. GA3 application at 50 ppm had no effect on scape elongation of dwarf plants. In each of 3 years, dwarf genotypes always produced scapes about half the length of normal ones. The marked expression stability of the dw 1 gene will facilitate its introduction into onion cultivars. Providing there is no negative pleiotropic effect, the dwarfness gene is expected to reduce lodging and, thus, improve mechanical harvest of onion seed. Chemical names used: 2-chloroethyl phosphoric acid (ethephon), gibberellic acid (GA3).
Kil Sun Yoo and Leonard M. Pike
Eric Watkins and William A. Meyer
Recently, turfgrass breeders have developed many improved turf-type tall fescue (Festuca arundinacea Schreb.) cultivars. Due to the large number of cultivars currently available to turfgrass managers and researchers, we have classified turf-type tall fescue cultivars into six groups based primarily on several morphological measurements. This type of classification is important for turfgrass breeders because many breeding decisions are made based on observations in a spaced-plant nursery. The major objective of this study was to classify tall fescue cultivars and selections based on spaced-plant measurements and to then compare those results with turf performance. A spaced-plant nursery consisting of 36 cultivars and selections was established in September 1998 at Adelphia, N.J. Plant height, panicle length, flag leaf width and length, subtending leaf width and length, and subtending internode length were measured 10 days after anthesis in 1999 and 2000. Additionally, a turf trial was established at North Brunswick, N.J., that included the same 36 cultivars and selections. The turf plots were evaluated for several traits including overall turfgrass quality, density, and susceptibility to brown patch disease. Based on principal component analysis of morphological measurements, along with turf trial data, all cultivars and selections were assigned to one of six groups: forage, early-standard, standard, early semi-dwarf, semi-dwarf, and dwarf. In turf plots, the semi-dwarf, early-semi dwarf, and dwarf groups were the top-performing types in terms of overall turfgrass quality, and the forage and early-standard cultivars had the lowest overall quality ratings. The dwarf types did not perform well under summer stress, especially in terms of brown patch disease incidence. The results of this study suggest that when developing cultivars for higher maintenance situations, turf-type tall fescue breeders should focus on the development of semi-dwarf cultivars.
Seeds of `Kumamotonokagayaki'(Kk), `Goldenball' (Gb), and `Purple Gem' (PG) (Zinnia violacea Cav.) were harvested at various stages of maturity and subsequent seed and plant performance were evaluated. The largest increase in ovule or embryo length and width occurred from 0 to 10 days after pollination (DAP). The seed weight was unchanged after 23, 25, and 30 DAP for Kk, Gb, and PG, respectively. The pericarp color was completely green from seeds harvested 20 DAP, while the seeds harvested from 30 to 35 DAP contained a mixture of green and brown seeds. Pericarp color change from green to brown was not a reliable index to harvest seeds. The percentage germination increased from seeds harvested from 10 to 19 DAP for all cultivars. From 20 to 40 DAP, germination was unaffected and >90%, while the rate of germination as measured by days to visible germination decreased slightly. Seeds harvested 20 to 40 DAP produced plants with similar growth and quality characteristics. Considering a 20- to 30-day difference between the first and last floret to open in a capitulum, capitula should be harvested 50 days after anthesis for good seed quality and to prevent shattering.
Mustafa M.A. Elballa and D.J. Cantliffe
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.