Abstract: Seed priming and drying condition effects were investigated immediately after seed-priming and 9 week after the storage. In this experiment, carrot seeds of `Forto C.V.` were used. These seeds were individually primed for 10 days at 20 °C and in PEG (6000) (273 g L-1) and KNO3 (200 mmol) solutions. Then they were dried for 1 and 2 h at 15, 25 and 30 °C, respectively. One part of the seeds was stored at 5 °C in RH/45% For 9 week. Chemical priming effects, drying temperature as well as germination temperature on different traits especially germination percentage were significant. However, drying time had no significant effect on germination percentage after storage period. PEG priming and drying at 25 °C for 2 h provided the best condition for germination percentage. Using the best material for pre-priming, along with suitable drying management with appropriate quality and good conditions of the storage is important.
INTRODUCTION
Normal carrot production requires uniform and quick germination. This would be feasible not only by seed quality, but also through especial pre-primings. Priming application especially under stress condition is very important (Bradford, 1986). Salinity resistance has especial importance in plant germination and growth periods. Studies on drought effects on germination are done in osmotic active solutions (Bradford and Haigh, 1994; Caseiro et al., 2004; Demir Kaya et al., 2006). There has been continuous flow of information for using pre-planting priming to improve germination and its speed in farm (Bradford and Haigh, 1994; Murungu et al., 2004). To do so, some researchers as such Heydecker and Coolbear (1977) and Bradford et al. (1988) have investigated different primings. One of these treatments is putting seeds into an osmotic solution. This method is done according to seed watering control in priming time and beginning of metabolite activity after observable germination; however, it prevents root exit (Nascimento and West, 2000). Some successful results on PEG application have been reported in different plant species as onion, maize, celery, carrot, radish, parsley, lettuce and tomato (Brocklehurst and Dearman, 1983a; Cantliffe et al., 1981). Studies show that priming duration and osmotic potential of applied solutions are important. Nowadays, priming of some species and their commercial usage are considered as a commercial technique of seed production (Goobkin, 1989; Maiti et al., 2006; Young and Pathi, 2007). Seeds drying are essential for storage. To commercialize primed seeds, drying seeds without decreasing their germination strength is important. To store primed seeds successfully drying usually necessitated, so that reduction of humidity depends on the species and storage condition (Nascimento and West, 2000).
In different species, the time and temperature of priming, time and temperature of environment and germination temperature are varied. This has been proved about watermelon and melon (Nascimento and West, 2000). So, the present investigating was therefore undertaken to determine the best temperature as well as drying condition on carrot.
MATERIALS AND METHODS
A study was conducted to evaluate the best temperature and dry condition in carrot primed-seeds in the Department of Horticulture, Faculty of Agriculture, Maragheh Higher Education Complex, University of Tabriz, during the year 2006.
Priming: The primed seed applied in this study was of carrot Forto cv. Four gram of the seeds was soaked in PEG (6000) solution with a concentration of 273 g L-1 (osmotic potential of -1.0 MPa) and inside KNO3 solution (200 mmol). The solutions were incubated at 20°C in an incubator. Priming time was 10 days.
Drying: After priming, seeds were individually dried for 1 and 2 h at 15, 25 and 30°C. After drying half of the seeds from each treatment were stored at 5°C and 45% humidity for 9 week. Reaming of the treated seeds was planted in Petri dishes.
Germination test: The above mentioned seeds were planted individually in 4 replications in 96 Petri dishes (10 cm dia). Fifty seeds were sterilized in 0.002 of Tiram solution and planted in each Petri plate. Four replications of each treatment, containing 2 pre-priming solutions, 3 drying temperatures and 2 drying times, were put in 2 separate incubators in front of light and at 15 and 20°C.
Data handling: Data time required for germination (by the use of formula, Σ(nxt)/Σ.n; where: n = No. of germinated seeds per day, t = No. of days germination taken place, Σn = Sum of germinated seeds in general) and T50 values were investigated. Fourteen days after incubation radicle length, dry weight of radicle and plumule dry were measured for each sample. To measure radicle and plumule dry weight were calculated by using an over at 68°C for 48 h and then all the samples were weighed in an electronic balance (0.0001 scales).
Post-storage period: Dried seeds that stored for 9 week at 5-7°C, were planted in 96 Petri dishes after sterilization as described earlier and then were incubated at 15 and 20°C. Observations were performed and samples were analyzed according to the first method. The data were analyzed with MSTATC and SPSS softwares. The experiment design was split factorial with 4 factors. Mean comparison was done by Duncan`s test (p = 0.01).
RESULTS
After priming: After priming, the seeds were kept at 15 and 20°C in order to germinating and all the data were observed for 14 days to achieve germination percentage, T50 and mean time required for germination (Table 1). Germination percentage was more observable with PEG 6000 compare to KNO3. All factors like chemicals (C), drying temperature (T), drying time (D) and their interactions were significant, except the interaction effects of TD (drying timexdrying temperature). PEG 6000 treatments dried at 25°C for 2 h and germinated at 20°C showed the better results comparers other treatments in the case of percentage germination.
The mean of dried radicle and plumule among different treatments had no significant difference. Germination at 20°C showed the best result among other
| Table 1: | Effect chemical treatments, temperature and time drying on different traits (pre-storage) |
| PG: Percentage Germination; LR: Radicle Length; DWR: Dry Weight of Radicle; DWP: Dry Weight of Plumule, NS, *, **Non significant, significant at p = 0.05 or 0.01, respectively | |
| Table 2: | Effect chemical treatments, temperature and time drying on different traits (post-storage) |
| PG: Percentage Germination; LR: Radicle Length; DWR: Dry Weight of Radicle; DWP: Dry Weight of Plumule, NS, *, **Non significant, significant at p = 0.05 or 0.01, respectively | |
treatments. The least germination time in the case of PEG was at 15°C and the highest speed of germination with KNO3 was also at 15°C.
After storage: after priming, the seeds were kept in storage for 9 week in order to investigate the storage effect on germination and other seed traits germination percentage, T50 value and mean of the germination time decreased after storing that after priming. Drying temperature was not significant on germination percentage, but in other features the opposite case was occurred, however, drying time had no significant effect on other traits (Table 2).
Seeds, primed with PEG (dried at 30°C for 2 h). Showed the highest percentage of germination at 15°C, but there was no difference significant between radicle and plumule dry weight. As a matte of fact, all the characters during the storing period showed a relative decrease after priming.
DISCUSSION
Drying temperature of primed seeds before storage is effective in germination percentage increase, but unstored seeds have higher germination percentage than stored ones. Drying temperature in string conditions has significant effect on germination percentage in other traits. The primed seeds in lettuce, dried at 27°C, had higher germination percentage than drying at 32°C (Guedes and Cantliffe, 1980). These was due to, probably, shield cracking at high drying temperature, this temperature (60°C) after seed soaking period, increased seed spoilage of radish in the storing period (Mude et al., 1994; Bekendam et al., 1987), showed that the storing conditions significantly affect on the shrubs growth whose seeds were under priming. Carpenter and Eoucher (1991) observed that primed pansies seeds were to aerated to drying only and germination of all the dehydrated seeds (9%) after 6 week of storage was decreased. Meanwhile germination in unprimed seeds were similar at 12-20% of humidity. As a result, seeds high humidity is effective on seeds strength maintenance and its survive in storage conditions.
Carrot seeds soaking in PEG increases germination percentage and decreases average germination time. Also, seed soaking in PEG increases significantly germination speed, unless the seeds are dried in lower temperatures. These results match with many reports. Most of then shows positive effects of some chemicals salts and PEG on many traits like germination percentage, germination speed and better settlements of shrubs in farm in onion and radish (Akers et al., 1987; Goobkin, 1989), lettuce (Cantliffe et al., 1981), carrot and celery (Brocklehurst and Dearman, 1983b). However, Cayuela et al. (2007) and Dahal et al. (2007) on tomato and Ellis and Butcher (2007) on onion confirmed the previous findings. Hence appropriate management of drying condition in carrot primed seeds with suitable chemicals and good germination temper true, along with good quality of seeds and appropriate condition in storage can provide good condition for germination and better growth.