The effects of chronic, mild heat stress on fruit set, fruit production, release of pollen grains, photosynthesis, night respiration, and anther dehiscence were ex-amined in tomatoes (Lycopersicon esculentum Mill.) differing in high temperature sensitivity. Plants were grown under three temperature regimes: 1) 28/22 or 26/22 °C (optimal temperature) 2) 32/26 °C (high temperature), and 3) 32/26 °C day/night temperatures relieved at 28/22 °C for 10 days before anthesis, then returned to 32/26 °C (relieving treatment). `FLA 7156' was the only cultivar with fruit set at 32/26 °C. All five cultivars, however, had fruit set in the relieving treatment (RT). The longer the relief, the higher was the percentage of fruit set. Longer periods of relief also increased the number of pollen grains released and linear regression analysis showed a significant relationship between the number of pollen grains released and the percentage of fruit set. Germination of pollen grains was also lowered in high-temperature-grown plants. The number of pollen grains produced, photosynthesis, and night respiration did not limit fruit set under chronic, mild heat stress, however. This suggested that cultivar differences in ability to release pollen and to produce viable pollen under heat stress are the most important factors determining their ability to set fruit.
M.M. Peet and S. Sato
Elsa Sánchez, Kathleen Kelley, and Lynn Butler
Eight edamame [Glycine max (L.) Merrill] cultivars were evaluated in the field in 2002, 2003, and 2004 to determine their suitability for growing in central Pennsylvania. Each cultivar was direct seeded and data collected included plant populations (percentage of stand) and marketable yields. Plant populations ranged from less than 1% to 81% and, with one exception in 2002, were below 80%. Eighty percent plant populations or higher are considered optimal. Based on sub-optimal plant populations, none of the edamame cultivars evaluated in the field were determined to be suitable for direct seeding in central Pennsylvania. The effect of temperature on seedling emergence, and therefore, plant populations was then studied. Four of the edamame cultivars used in the field trial were evaluated in growth chambers programmed with varying day/night temperature regimes. Seedling emergence varied by cultivar and was generally below 80% with two exceptions. When grown in a 21.1 °C day/15.6 °C night temperature regime, `Butterbeans' and `Early Hakucho' exceeded 80% seedling emergence. These methods could be used to produce transplants; however, the economic feasibility of doing so should first be evaluated. In the field trial, conclusions on marketable yields were unattainable because soybean plants are known to compensate in yield for plants missing in sub-optimal plant populations. Plant compensation and sub-optimal plant populations rendered yield comparisons between cultivars questionable. The issue of sub-optimal seedling emergence and plant population needs to be studied further before suitability of growing these edamame cultivars in central Pennsylvania can be determined.
Patricio A. Brevis, D. Scott NeSmith, and Hazel Wetzstein
Effective pollination period (EPP) is the number of days during which pollination is effective to produce a fruit. The EPP is determined by ovule longevity, pollen tube growth rate and length of stigmatic receptivity. The objectives of this research were to establish the EPP of rabbiteye blueberry and to further the understanding of its limiting parameters. The experiments were conducted in growth chambers using blueberry plants of the cultivars Brightwell and Tifblue. Emasculated flowers were hand-pollinated at 0, 2, 4, 6, and 8 days after anthesis (DAA). Ripe fruit were harvested to record percentage fruit set. Stigmatic receptivity was evaluated as the number of germinated tetrads on the stigma 24 hours after pollination. Under day/night temperatures of 23/10 °C, the EPP was 7 days. Stigmatic receptivity was lowest on the day of anthesis and increased as flowers aged. Stigmatic receptivity was not positively correlated to fruit set, therefore, this parameter was not the most limiting factor of the EPP. Observations of pistils pollinated 3 DAA indicated that the fastest growing pollen tubes reached the bottom of the style 2 to 3 days after pollination. Self-pollination resulted in normal pollen tube growth in the style and inside the ovary. Self-pollen tubes were seen penetrating the micropile.
Erika K. Gubrium, Donna J. Clevenger, David G. Clark, James E. Barrett, and Terril A. Nell
A series of experiments on ethylene-insensitive (EI) petunia plants (Petunia ×hybrida Hort. Vilm.-Andr.) generated in two genetic backgrounds were conducted to determine the involvement of ethylene in horticultural performance. Experiments examined various aspects of horticultural performance: days to flower, flower senescence after pollination and without pollination, fruit set and ripening, and adventitious root formation on vegetative stem cuttings. The development of EI plants was altered in several ways. Time from seed sowing to first flower anthesis was decreased by a week for EI plants grown at 26/21 °C. Flower senescence in nonpollinated and self-pollinated flowers was delayed in all EI plants compared to wild-type plants. Fruit set percentage on EI plants was slightly lower than on wild-type plants and fruit ripening on EI plants was delayed by up to 7 days. EI plants produced fewer commercially acceptable rooted cuttings than wild-type plants. There was a basic difference in the horticultural performance of the two EI lines examined due to a difference in the genetic backgrounds used to generate the lines. EI plants displayed better horticultural performance when grown with day/night temperatures of 26/21 °C than 30/24 °C. These results suggest that tissue-specific ethylene insensitivity as well as careful consideration of the genetic background used in transformation procedures and growth conditions of etr1-1 plants will be required to produce commercially viable transgenic floriculture crops. EI petunias provide an ideal model system for studying the role of ethylene in regulating various aspects of plant reproduction.
K.M. Rainey and P.D. Griffiths
Yield components of 24 common bean (Phaseolus vulgaris L.) genotypes were evaluated following exposure during reproductive development to four greenhouse day/night temperature treatments (24 °C/21 °C, 27 °C/24 °C, 30 °C/27 °C and 33 °C/30 °C). Genotypes included 12 snap beans, two wax beans, six dry beans, and four common bean accessions; 18 genotypes were previously described as heat-tolerant and three were heat-sensitive controls. The highest temperature treatment reduced seed number, pod number, mean seed weight and seeds/pod an average of 83%, 63%, 47%, and 73%, respectively. A heat susceptibility index (S) measuring yield stability under high temperatures indicated that `Brio', `Carson', `G122', `HB 1880', `HT 20', `HT 38', `Opus', and `Venture' were heat tolerant. Heat-tolerant genotypes displayed differential responses to high temperature, suggesting different genetic control of heat tolerance mechanisms. Genotypes with moderate heat tolerance, including `Barrier' and `Hystyle', showed stable yields in the 30 °C/27 °C treatment only, indicating this regime is optimal for screening common bean materials of unknown heat tolerance. `Haibushi', `Indeterminate Jamaica Red', and `Tío Canela-75' were previously described as heat tolerant but exhibited a heat-sensitive reaction in this study. Heat-sensitive genotypes `Haibushi' and `Labrador' maintained mean seed weight under high temperature. This data will help utilize nonallelic heat tolerance genes in development of bean varieties grown in high temperature environments.
Sorkel Kadir and Robert Wample
Evaluation of thermostability of photosynthetic apparatus of intact leaves and isolated thylakoids of five cultivars of wine grapes (Vitis vinifera) was conducted. Four- week- old plants of Semillon, Chenin Blnac, Pinot Noir, Chardonnay, and White Riesling, were placed into a control environment chamber held at 20/15° 30/25°, and 40/35 °C day/night temperature for 14 days. Induced (F0), variable (Fv), and maximum fluorescence (Fm) and the quantum yield of net photosynthesis (Fv/Fm) were measured after 1-14 days exposure. All fluorescence parameters were not affected by 20/15° and 30/25°C. However, high temperature (40/35°C) increased F0 and decreased Fm, Fv, and Fv/Fm. These changes were severe in Semillon and Chenin Blanc, moderate in Chardonnay and White Riesling and scarce in Pinot Noir. Average high temperature data that are experienced in Yakima Valley area will be presented. Isolated thylakoid membranes from the cultivars were heated at 20-40°C. and uncoupled electron transport was determined. Thylakoid stability to heating varied similarly to whole-plant response to high temperature.
Richard K. Schoellhorn, James E. Barrett, and Terril A. Nell
`Improved Mefo' chrysanthemums were grown at 22C/18C and 34C/28C day/night temperature regimes to evaluate the failure of lateral bud development following pinching of this temperature sensitive cultivar. The number of viable buds on plants at the high temperatures was 40% of number at low temperature. Loss of bud viability was categorized as those buds that were: 1) absent, or 2) those in which growth was present, but inhibited. Inhibited buds were visible swellings surrounded by dense masses of secondary cell wall material. Anatomical studies were completed to verify the absence of lateral buds and determine what cellular changes imposed inhibition on those buds that did develop. A second group of experiments demonstrated that moving low-temperature plants to the high temperature caused production of viable buds to decline. Plants were moved from high temperatures to low, and reciprocally to high from low temperature. Anatomical sampling of apical meristems began at time of shift and at 1, 2, 4, and 8 days after temperature shift. High-temperature meristems possessed predominantly non-viable lateral buds, with few viable buds present.
Douglas D. Archbold
Plants of a diverse collection of Fragaria clones from a range of native habitats representing F. chiloensis, F. virginiana, F. virginiana glauca, and F. vesca, were grown in a controlled environment at one of three day/night temperatures, 15/15, 23/15, or 31/15°C. Relative growth rate (RGR) and net assimilation rate (NAR) were estimated from plant leaf areas and total dry weights. At 23/15°C, the species mean RGR and NAR values were comparable although clones within species exhibited significant variation. At 15/15 and 31/15°C, RGR and NAR for species were lower than at 23/15°C. At 31/15°C, chiloensis and vesca mean values were reduced more than the others, to less than 50% the 23/15°C values. Also, NAR declined most for chiloensis, to 45% the 23/15°C value. At 15/15°C, virginiana had much higher RGR and NAR values than the other species, and its NAR mean value was greater than at 23/15°C. Although the species means would suggest that there are interspecific differences in temperature response, intraspecific variability was also large. Thus, classifying Fragaria species by temperature response may be an over-generalization.
Donglin Zhang, A.M. Armitage, J.M. Affolter, and M.A. Dirr
Platycodon grandiflorus (Jacq.) A. DC. `Sentimental Blue' can be used as a pot plant and garden perennial. Plants can be grown year-round in a greenhouse as cutting flowers if supplemental heat is provided in the winter. Sowing time did not affect plant growth and flowering. Seeds took 10 to 20 days to germinate at 20–25 °C day/15–20 °C night temperatures. As the day/night temperature decreased, time to germination increased and germination rate decreased. Temperature also influenced shoot proliferation and number of basal branches increased as temperature decreased. Plants reached reproductive growth about 20 days after transplanting and took another 20 days to reach full bloom. Open flowers lasted 3–7 days. Cold treatment was not necessary for flowering, but plants were forced into dormancy when provided with 5 °C for 4 or more weeks. Plants began to emerge 2 to 3 months later and two growth forms, “rosette” and “dwarf”, occurred in the second growth cycle. The dwarf form produced one or two stems with six to eight clustered flowers per stem while the rosette form produced an average of 10 stems with one or two flower per stem. For the “rosette” form, each stem could be divided as a new plant.
Tracy A. Ohler and Cary A. Mitchell
The vigorous growth habit and tolerances to heat, water, and acid stresses suggest cowpea as a candidate species for Controlled Ecological Life-Support Systems (CELSS). The low fat, high protein, moderate carbohydrate content of the edible leaves and seeds complement cereal grains in the vegetarian diets planned for CELSS. Cowpea canopy densities of 3.6, 7.2, 10.7, and 14.3 plants·m-2 were grown under CO2 levels of 400 or 1200 μl·l-1. Plants were grown in a deep-batch recirculating hydroponic system. pH was maintained at 5.5 by a pH controller with an in-line electrode. The nutrient solution was replaced as needed and sampled weekly for analysis by inductively coupled plasmaatomic emission spectrometry. Fluorescent lights provided 674±147 μmol·m-2s-1 PAR for an 8-hour photoperiod. Day/night temperature was maintained at 27/25°C. CO2 draw-down within the growth chamber was measured to calculate net photosynthesis. Power consumption was metered and canopy quantum efficiency was calculated. Crop yield rate (g·m-2·d-1). harvest index (% edible biomass), and yield efficiency (edible g·m-2·d-1·(nonedible g)-1) were determined to evaluate the productivity of cowpea for a CELSS. This study was supported by NASA Grant NAGW-2329.