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Ahmet Korkmaz

The effects of incorporating plant growth regulators into the priming solution on low temperature germination and emergence percentage performance of sweet pepper (Capsicum annuum `Demre') seeds before and after seed storage were investigated. Seeds were primed in 3% KNO3 solution for 6 days at 25 °C in darkness containing one of the following: 1, 3, 5, or 10 μm methyl jasmonate (MeJA) or 0.05, 0.1, 0.5, or 1 mm acetyl salicylic acid (ASA). Following priming, seeds were either immediately subjected to germination and emergence tests at 15 °C or stored at 4 °C for 1 month after which they were subjected to germination test at 15 °C. Priming pepper seeds in the presence or absence of plant growth regulators in general improved final germination percentage (FGP), germination rate (G50) and germination synchrony (G10-90) at 15 °C compared to nonprimed seeds which had an FGP of 44%, G50 of 7.3 days and G10-90 of 7.3 days. Priming seeds in KNO3 solution containing 0.1 mm of ASA resulted in the highest germination percentage (91%), fastest germination rate (G50 = 2.2 days) and the most synchronous germination (G10-90 = 6.1 days). Emergence percentages were the highest for the seeds primed in the presence of 0.1 mm ASA (85%) and 3 μm MeJA (84%) while nonprimed seeds had an emergence percentage of 40%. Fastest emergence rates (E50) were also obtained from seeds primed in KNO3 supplemented with 3 μm MeJA (E50 = 15.2 days) and 0.1 mm ASA (E50 = 15.2 days). Shoot fresh and dry weights of pepper seedlings were significantly affected by priming treatments and priming in the presence of 0.1 mm ASA resulted in highest seedling shoot fresh and dry weights. Although all priming treatments improved germination performance of pepper seeds at 15 °C following 1 month of storage, inclusion of 0.1 mm ASA into the priming solution resulted in the highest germination percentage (84%) and germination rate (G50 = 3.8 days). These results indicate that priming seeds in 0.1 mm of ASA or 3 μm MeJA incorporated into the KNO3 solution can be used as an effective method to improve low temperature performance of sweet pepper seeds and that these seeds can be stored for 1 month at 4 °C and still exhibit improved germination performance at 15 °C.

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Ahmet Korkmaz and Wallace Pill

Achievement of head size uniformity at final harvest reduces loss and increases profitability for the hydroponic lettuce grower. Shoot fresh weight of `Cortina' lettuce (Lactuca sativa L.) at 7 or 21 days after planting (DAP) was inversely proportional to the number of days required for seedling emergence, and was greater for raw than for pelleted seeds. Head fresh weight at final harvest (61 DAP) was directly proportional to seedling length at 21 DAP, but raw and pelleted seeds produced equal head weights. Thus, initial seed (seedling) vigor differences were maintained to final harvest. Osmotic seed priming (–1.5 MPa KH2PO4, 20 h, dark) led to increased germination rate at 15, 25, and 35C; had no effect on germination synchrony; and increased germination percentage only at 35C. Covering raw or pelleted seeds sown in depressions of the phenolic foam trays with fine (No. 5) vermiculite compared to leaving the seeds uncovered, and soaking the trays in hydroponic solution rather than water, increased seedling shoot fresh weights. Seeds sown on their first day of germination or primed seeds gave greater seedling shoot fresh weights than pelleted seeds. However, the more uniform seedling shoot fresh weights from germinated seeds than from primed seeds was associated with more rapid and synchronous seedling emergence.

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Ahmet Korkmaz and Robert J. Dufault

Muskmelon (Cucumis melo) seedlings are transplanted in late winter or early spring before last frost date to ensure early yields; however, this makes them very vulnerable to temperatures cycling between almost freezing and optimal temperatures. To simulate temperature alternations that may occur after field transplanting, `Athena', `Sugar Bowl', `Eclipse' muskmelon, and `Tesorro Dulce' honeydew (C. melo) transplants were subjected to 2 ± 1 °C (35.6 ± 1.8 °F) in a walk-in cooler and then to 29 ± 5 °C (84.2 ± 9.0 °F) in a greenhouse before field planting. In 1998, transplants were exposed to 2 °C for 9 to 54 hours, and for 9 to 81 hours in 1999. `Athena' and `Sugar Bowl' yielded less early melons in both years, whereas `Eclipse' and `Tesoro Dulce' early yields were only reduced in 1999. Total yields of `Athena' decreased linearly in both years with 10% yield reduction occurring with 12 to 21 hours of cold stress. Total yields of `Sugar Bowl' decreased linearly in both years with 11 to 18 hours of cold stress causing 10% yield reduction in 1998 and 1999, respectively. Therefore, early planting before last frosts of all these muskmelon and honeydew cultivars should be done with caution since reductions in early yields are highly probable.

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Ahmet Korkmaz and Robert J. Dufault

Cantaloupe seedlings may be repeatedly exposed in the field soon after transplanting to temperatures alternating between almost freezing and optimal temperatures. In the first year of a 2-year study, `Athena' cantaloupe seedlings were exposed in walk-in coolers to temperatures cycling from 2 °C for 3, 6, and 9 hours daily to 25 °C for the rest of the 24-h period. Cold stress was repeated for 1, 3, 6, and 9 days before field planting. In the second year, transplants were exposed to 2 °C for 3, 6, and 9 hours for 3, 6, and 9 days before field transplanting. The objective of this study was to determine the long-term effect of early season cold temperature exposure on seedling growth, earliness, yield and quality by simulating the cold/warm alternations possible in the field in coolers. Cold-stressed transplants were planted in the field after all risk of ambient cold stress was negligible. In both years, exposure to cycling cold temperatures generally did not effect total productivity and fruit quality, although seedling growth characteristics were reduced in response to longer cold-stress treatments. In the second year, early yield was reduced by exposure to increasing hours of cold stress, but this was not significant in the first year. Therefore, cold temperature stresses occurring in the field at transplanting have negligible effect on yield potential of `Athena' cantaloupe.

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Ahmet Korkmaz and Robert J. Dufault

Watermelon [Citrullus lanatus (Thunb) Matsum. & Nakai.] seedlings may be repeatedly exposed to temperatures alternating between almost freezing and optimum soon after field transplanting. `Carnival', `Crimson Sweet', `Millionaire' and `Crimson Trio' watermelon transplants were exposed to cold temperature stress at 2 ± 1 °C in a walk-in cooler and then to 29 ± 5 °C in a greenhouse immediately before field planting to simulate temperature alternations that may occur after field transplanting. Cold-stressed transplants were field planted after all risk of ambient cold stress passed. In 1998, transplants were exposed to 2 °C from 9 hours to 54 hours, and in 1999 from 9 to 81 hours. Early yields of all cultivars, except Carnival, significantly decreased with increasing hours of cold stress in both years. Total yields of `Carnival' decreased linearly in both years with a 10% yield reduction occurring from 14 to 15 hours of cold stress. `Crimson Sweet' yields were reduced in 1999 only, with 16 hours of cold stress reducing yield 10%.

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Ahmet Korkmaz and Robert J. Dufault

Watermelon (Citrullus lanatus (Thunb.) Matsum. and Nakai) seedlings transplanted before the last frost date may be exposed to temperatures alternating between freezing and optimal until field temperatures finally stabilize. Cold stress may ultimately reduce growth and yield. To simulate such temperature alternations that occur naturally after field transplanting, diploid `Carnival' watermelon seedlings were exposed immediately before field planting to cyclic cold temperature stress at 2 ± 1 °C then transferred to a greenhouse at 29 ± 5 °C. In 1997, transplants were exposed to 2 °C from 3 to 81 hours and in 1998, exposure ranged from 9 to 81 hours. Cold-stressed seedlings were field planted after all potential risk of cold stress in the field had passed. In 1997, cold stress decreased seedling shoot and root fresh and dry weights, leaf area, chlorophyll and carbohydrate contents but not seedling height. In 1998, all seedling growth variables decreased in response to longer durations of cold stress. Plants cold stressed for up to 81 hours transpired more for 1 week after transplanting than those exposed to shorter periods of cold stress. In both years, vining (date first runner touched the ground), flowering, and fruit set were delayed significantly as cold stress hours increased. Although early yields were unaffected, total yields decreased linearly in both years with increasing hours of cold, with 38 to 40 hours of cold stress reducing yield 10% in both years. Data indicate that `Carnival' watermelon transplants exposed to cold stress soon after transplanting may suffer yield reductions.

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Ahmet Korkmaz and Robert J. Dufault

For the earliest yields of spring melons, muskmelon [Cucumis melo L. (Reticulatus Group)] fields in the southeast United States may be transplanted in late winter before the last frost date. Seedlings may be exposed to cold temperatures cycling between almost freezing and optimal for weeks before warm weather predominates and such exposure may reduce later growth and yields. To test whether cold stress may reduce growth and yield, `Athena' muskmelon seedlings were subjected to cold stress at 2 ± 1 °C then transferred to a greenhouse at 29 ± 5 °C before field transplanting. In 1997, cold exposure durations were 3, 6, or 9 h and were repeated (frequency) for 1, 3, 6, or 9 d before transplanting. In 1998, duration levels were not changed but frequencies were 3, 6, or 9 d. In 1997, as cold stress increased, seedling shoot and root fresh and dry weights, height, leaf area, and leaf chlorophyll content decreased linearly, but shoot carbohydrates decreased curvilinearly and stabilized with ≈54 hours cold stress. In 1998, all seedling growth characteristics except leaf chlorophyll content decreased linearly as cold stress exposure increased. Leaf chlorophyll content decreased curvilinearly as cold stress increased to 36 h, but leveled off with more hours of cold stress. Even 1 week after transplanting, plants exposed to cold stress for up to 81 h continued to transpire more than control plants. In both years, vining (date first runner touched the ground) and male and female flowering were delayed significantly with increasing cold stress, but fruit set was affected only in 1998. Cold stress in 1998 delayed earliness with early fruit weight and number per plot decreasing as cold stress exposure increased. Total yields decreased linearly in both years as cold stress increased with 21 to 32 hours causing 10% yield reduction in 1997 and 1998, respectively. Results indicate a potential risk exists for yield reduction if `Athena' muskmelon is planted weeks before last frost dates.

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Ahmet Korkmaz, Wallace G. Pill and Bruce B. Cobb

Raw, pelleted or germinated seeds of `Cortina' lettuce (Lactuca sativa L.) were sown in phenolic foam cubes preplant soaked in water or fullstrength nutrient solution (2 mmho·cm−1, 2 dS·m−1). The seeds were left uncovered or covered with fine vermiculite (grade 5), and seedling emergence characteristics were subsequently determined. Shoot fresh masses and their coefficients of variation (cv) by 9 days after planting (1 or 2 true leaves) and by 31 days after planting (4 or 5 true leaves) also were determined. Soaking the cubes in nutrient solution rather than water increased seedling emergence percentage and rate, and increased shoot fresh masses by 9 or 31 days after planting. This increased shoot fresh mass was accompanied by lower cv of shoot fresh mass by 9 days after planting, but not by 31 days after planting. Covering seeds with vermiculite decreased emergence from 99% to 93%, but increased shoot fresh mass by 9 and 31 days after planting when cubes were soaked in water, but not in nutrient solution. Seed treatments influenced shoot fresh mass at 9 and 31 days after planting in the order germinated > pelleted > raw. Germinated seeds resulted in lower cv of shoot fresh mass (24%) than raw or pelleted seeds (29%) by 31 days after planting. Thus, sowing germinated seeds into foam cubes soaked in full-strength nutrient solution, with or without covering the seeds with vermiculite, produced the heaviest and most uniform seedlings.

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Ahmet Korkmaz, Mehmet Nuri Nas, Nusret Ozbay and Iskender Tiryaki

The effects of stratification and priming on germination and emergence performance of narrowleafed purple coneflower (Echinacea angustifolia) seeds were investigated. Seeds were pre-chilled for 3 weeks at 4 ± 0.5 °C (39.2 ± 0.9 °F) in light or primed for 3 days at 20 ± 0.5 °C (68.0 ± 0.9 °F) in darkness in Nas and Read medium (NRM) or in 2% potassium nitrate (KNO3) supplemented with 3 or 5 μm 1-aminocyclopropane carboxylic acid (ACC) or 500 mg·L-1 (ppm) or 1000 mg·L-1 gibberellic acid (GA3). Following stratification and priming, seeds were subjected to germination and emergence tests at 25 ± 0.5 °C (77.0 ± 0.9 °F). Priming the seeds in NRM or KNO3 containing 3 μm ACC gave the highest germination percentages with 78% and 80%, respectively. Stratification alone increased germination to 69% compared to nontreated seeds, which had the lowest germination percentage of 57%. Emergence was enhanced by priming seeds in the presence of 3 μm ACC (75%) compared to stratified seeds (62%), while nontreated seeds had the lowest emergence percentage of 26%. These results indicate that priming in the presence of ACC might be an alternative to lengthy stratification treatments to break the dormancy and improve the germination and emergence of narrow-leafed purple coneflower seeds.

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Ahmet Korkmaz, Wallace G. Pill and Bruce B. Cobb

The effect of seed germination rate, or of seedling emergence rate, was studied in relation to subsequent plant growth of `Cortina' lettuce (Lactuca sativa L.). Seedling growth response to selection by time of germination was assessed by imbibing seeds at 5 °C to increase the time range for germination. Germinated seeds were removed daily and transferred to “slants” (germination paper held at 20° from vertical) at 15 °C. Five days after each transfer, root and hypocotyl lengths were measured. As days required for germination increased, root lengths decreased and hypocotyl lengths increased, resulting in no change in total seedling length. The relation between rate of seedling emergence from raw or pelleted seeds of the same lot and shoot fresh weight was examined using commercially practiced hydroponic techniques. Shoot fresh weight at 10 and 21 days after planting was related inversely and linearly to the day of emergence for both seed treatments. In the same study, the coefficient of variation of shoot fresh weight was positively related to time of seedling emergence only at 10 days. Germinated seeds were selected after 1 and 2 days of imbibition; subsequent seedling emergence rate and shoot fresh weight at 25 days were recorded. First-day germinated seeds had faster and more synchronous emergence, and produced heavier and more uniform shoots. Discarding slow-to-germinate seeds should enhance seedling emergence and growth.