1076 J. AMER. SOC. HORT. SCI. 121(6):1076–1081. 1996. J. AMER. SOC. HORT. SCI. 121(6):1076–1081. 1996. Alteration of Seedstalk Development, Seed Yield, and Seed Quality in Carrot by Varying Temperature during Seed Growth and Development Mustafa M.A. Elballa 1 and D.J. Cantliffe Horticultural Sciences Department, IFAS, University of Florida, Gainesville, FL 32611 Additional index words. germination, Daucus carota, seed production, seed vigor, accelerated aging Abstract. 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. The purpose of the present study was to investigate the effect of different growing temperatures on seedstalk development, seed yield, and seed quality in carrots. Materials and Methods Carrot (Daucus carota ‘Hicolar 9’) stecklings were grown on raised beds at the Horticultural Unit at the Univ. of Florida, Gainesville, on a fine sandy soil. After harvest in August, medium, uniform stecklings were selected and washed, and tops were cut to about 6 cm long and roots to about 12 cm long. Stecklings were dipped in 0.2% Thiram solution and stored in vermiculite mixture for 8 weeks at 5 °C (Elballa and Cantliffe, 1987). Experiment 1: The influence of growing temperature on seedstalk development, seed yield, and seed quality. Carrot stecklings were planted in 8-L pots filled with 3 peat : 1 perlite mixture and grown in a greenhouse under a 14-h photoperiod at 25/20 °C day/night temperatures. At seedstalk initiation, uniform plants were trans- ferred to growth chambers (Conviron E-15) in which the day/night temperatures were set at 33/28, 28/23, 25/20, 23/18, 20/15, and 17/ 12 °C. Light intensities of 775 and 600 μmol·m –2 ·s –1 at the primary umbel level and the pot level, respectively, and photoperiod (14 h) were provided equally in all chambers. Plants were fertilized every week with a 20N–9P–17K solution applied through a drip system at a rate of 20 g/3.7 L. Each plant received 200 mL of this solution. Otherwise, general irrigation was done when needed. Relative humidity (RH) was maintained at 70% during vegetative and early reproductive stages, then reduced to 40% when seeds on the primary umbel started to mature. The experiment was a completely randomized design, with 10 replicates (plants) in each chamber. Plants were tagged at the date of anthesis of the first flower on the primary umbel. Flowers were hand-pollinated in the morning and late afternoon. Seeds were harvested when those on the tertiary umbels reached maturity (i.e., after 55, 70, and 90 d from primary umbel anthesis for 33/28, 28/33 °C, and all remaining treatments, respectively). They were then threshed, cleaned by hand and stored at 10 °C and 20% RH. Germination and mean days to germination (MDG) were deter- Seed yield, seed quality, and seedling vigor are influenced by the growing environment of the mother plant (Austin, 1972). Effects of temperature on flower initiation, flowering, and seed production of many agronomic and horticultural crops has long been recognized (Went, 1953). Temperature appears to be the primary environmental factor that influences a seed crop from the vegetative phase to all stages of seed development and maturation. Moderate to high seed maturation temperatures, compared to seed that matured under cool conditions, increased the germination capacity of freshly harvested seeds of sugarbeet (Wood et al., 1980), lettuce (Harrington and Thompson, 1952; Koller, 1962), barley (Khan and Laude, 1969), forage grasses (Akpan and Bean, 1977), hybrid rose (Van Abrams and Hand, 1956), and alfalfa (Austin, 1972). Research on carrot seed production has dealt mainly with temperature effects during the early stages of seed development such as flower initiation, seedstalk development, and sex expres- sion. Sakr and Thompson (1942) reported that growth tempera- tures of 10 to 15 °C following vernalization resulted in 60% to 100% flowering and was more favorable to reproductive growth in ‘French Forcing’ carrot than 15 to 21 or 21 to 27 °C. Dickson and Peterson (1958) found that, following cold storage of the roots, plants grown at 13 °C bolted earlier and produced more flowers than those plants grown at 18 °C. Quagliotti (1967) studied the influence of temperature on seedstalk development and sex expression in ‘Amsterdam Forc- ing’ carrot. At high temperature (26 °C), plants flowered earlier, but the seedstalk was weak. At low growing temperature (14 °C), the total number of flowers and fertile hermaphroditic flowers were more than twice the number obtained at 26 °C. The proportion of male flowers was higher at 26 than 14 °C. Eisa and Wallace (1969) reported that high temperature increased petaloidy in carrots and decreased seedstalk height. Received for publication 20 Feb. 1996. Accepted for publication 22 June 1996. Florida Agricultural Experiment Station journal series R-05016. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. 1 Current address: Dept. of Horticulture, Faculty of Agriculture, Shambat, Sudan.