Consequences of sowing dates and umbel pinching on Daucas carota seed production

This research was laid out to examine the effect of sowing dates and umbel pinching on seed production of Daucas carota. The experiment was conducted in randomized complete block design (RCBD) with split plot arrangement and replicated three times at Horticulture Nursery of Agriculture University, Peshawar, Pakistan in 2016. Sowing dates (25 October, 9 and 24 November) were assigned to main plot, while umbel pinching levels; secondary + tertiary + quaternary (STQ), primary + tertiary + quaternary (PTQ) and tertiary and quaternary (TQ) umbel pinching were allotted to sub plots. Maximum (p<0.05) days to flowering (111 days), plant height (137.5 cm), days to seed setting (15.6 days), umbel diameter (14.6 cm), days to maturity (151 days), variability in harvest time (34.8 days), seed yield umbel (5.1 g), seed yield plant (34.2 g) and seed yield tha (3.7 t ha) were recorded on 25 October sowing date. Umbel pinching had significantly enhanced plant height (136.4cm), umbel diameter (17 cm), and seed yield umbel (5.7 g) by pinching of STQ umbels. While, maximum seed yield plant 1 (46.9 g), seed yield t ha (5 t ha) and variability in harvest time (34.1 days) were observed in TQ umbel pinching. Interaction between sowing dates and umbel pinching (S x U) were found significant in case of seed yield umbel, seed yield plant, seed yield t ha and variability in harvest time. Based on the present findings it is concluded that sowing on 25 October with pinching of TQ umbels is recommended for maximum seed production in carrot.


Introduction
Carrot (Daucas carota L.) belongs to the family Umbellifereae, cultivated mostly as winter vegetable. It is originated in Asia and Mediterranean regions about 2000 years ago but nowadays cultivated throughout the world [1]. Carrot is considered as a temperate region crop that grows during spring in temperate regions while grows during winter in tropical and subtropical regions [2]. Carrot is a biennial crop but in tropical regions it is cultivated as an annual crop. An enlarged, high nutritive and fleshy taproot is produced by carrot plant which is edible. Carrot is a rich source of antioxidants, minerals, vitamins, and fibers, contains Vitamin A and βcarotene in large quantity [3].
Daucus carota L. produces rosette of leaves and taproot during the first growing season, while in the second growing season it develop flowers. Stored sugar provides energy to the plant for flowering. Carrot produces hermaphroditic and selfpollinated flowers but cross-pollination also occurs more frequently because stamens mature earlier than the pistils [4,5]. At the blooming stage, carrot produces an inflorescence on the tip of the stem called primary umbel which upon division makes the secondary, tertiary and quaternary umbels. Carrot seed quality such as size, vigor and germination changed as umbel order changes. The increase in umbel order decreased its size [1]. In carrot seed production, different umbel orders contribute differently. Primary umbel contributes 11%, secondary umbel 58% and tertiary 31% to the over-all seed production. Increase in the order of umbel causes decrease in the seed quality [6]. Seed quality depends on umbel size and its position [7]. Pinching is an important practice for the successful production of flowers. Pinching is actually the removal of terminal portion of stem to inhabit apical dominance. Pinching of growing shoot apex terminates the apical dominance and dry matter is diverted into side buds and branches. The two important factors that have great effect on carrot seed quality and yield are umbel order and umbel pinching. The purpose of umbel pinching is balancing and inducing the nutrients and hormones. When umbel pinching is done, the existing umbels have less competition for nutrients and hormones. Due to umbel pinching more nutrients and hormones are transported to the flowers which in turn grow healthy seeds [8]. The transport of auxin from the tissues might limit cytokynin concentrations as well as maintain apical dominance through hormonal action. Through pinching practice we can adjust plant growth and improve its quality. Apical control is a problem to the commercial growers because it does not allow the lateral buds to grow, which result in less number of lateral flowers. one can also increase the aesthetic value through pinching because of pinching practice more number of lateral flowers are produce [9]. Growth and yield of a crop are highly affected by sowing dates. The appropriate sowing time depends on cropping model and current environment which is an important factor for seed production of carrot. Being a biennial crop carrot seeds production is greatly affected by temperature [10]. Large size seeds produce heavier individual root weight and more resultant yield [11][12][13][14]. Keeping in view the importance of sowing dates and umbel pinching, the present study was conducted to test the hypothesis that sowing time, umbel pinching and their interaction have an influence on seed production in carrot.

Materials and methods Experimental site
We conducted current experiment at Ornamental Horticulture Nursery, The University of Agriculture, Peshawar, Pakistan in 2016, which is located at 71.5833 ° E longitude and 34.0167 ° N latitude with altitude above sea level is 350m. The climatic conditions in this location is semiarid, where maximum wind speed is 35 km/h, average annual rainfall is low (300 to 500 mm) 60-70% in summer while 30-40% rainfall occurs in winter [15,16].

Experimental design
The experiment was designed using RCBD (randomized complete block design) with split-plot arrangement having two factors and replicated three times. Seeds of cultivar "Shan"(collected from horticulture nursery) was sowed on three different dates i.e. 25 th October, 09 th November and 24 th November kept in main plot and different pinching levels i.e. pinching STQ umbels (secondary + tertiary + quaternary), PTQ umbels (primary + tertiary + quaternary) and TQ umbels (tertiary + quaternary) was allotted in sub plot. Twelve treatment combinations were kept, which were replicated three times. Row to row and plant to plant distance was kept 60 cm and 20 cm, respectively. There were 36 sub plots with plot size 1.4 m 2 each. Soil preparation Soil was ploughed up thoroughly and was leveled through cutter. One foot high ridges were made. A soil sample was collected before sowing and was send to soil laboratory for chemical analysis. Fertilization was done in split doses.
Recommended NPK doses were applied @ of 100, 100 and 125 kg ha -1 . Half dose of Urea and a full dose of Potash and Phosphorus were applied at sowing time and the rest of the urea was applied after 30 days of sowing. Irrigation was done when needed. Regular cultural practices i.e. weeding, hoeing etc were carried out throughout the experiment (Table 1).

Parameters recorded
Data recorded on different growth and productivity parameters during course of the studies include; Days to flowering, average plant height (cm) and umbel diameter (cm) were recorded by randomly selected five plants in each treatment per replication and their average was calculated. Days to seed setting were counted from the appearance of flower umbel to the date of seed setting, days to maturity were counted from the date of sowing to the seed harvesting maturity, variability in harvest time was calculated by subtracting the number of days to the maturity of first umbel from the number of days required for the maturity of last umbel in each treatment in every replication and their average was calculated. Seed yield per umbel -1 (g) and seed yield plant -1 (g) was taken by weighing the seed collected from five plants randomly in all treatments in each replication and their average was noted [17] while seed yield (tons ha -1 ) was calculated using following formula; Seed yield (t ha −1 ) = Plot seed yield (kg) Plot area (m 2 ) × 10000 1000

Statistical analysis
The data noted was subjected to Analysis of Variance (ANOVA) technique appropriate for RCBD split plot design with two factor experiment. Means were compared by using Least Significant Difference (LSD) test at 5% level of significance. Statistical software Statistix (8.1) was used for calculating ANOVA and LSD value [18,19].

Results and discussion Days to flowering
The mean data regarding days to flowering is presented in (  investigations who reported that umbel diameter in onion is affected by delay in planting. Early planting increased umbel diameter in onion compared to late planted onions. This might be attributed due to the climatic variability in growing environment [30]. Through umbel pinching practice, nutrients and hormones get balanced and diverted toward the remaining umbels giving a higher umbel size, more numbers of umbellate per umbel and ultimately produces higher yield. Pinching breaks apical dominance and diverts more energy to the production of more number of branches, flowers and ultimately more yield [28]. [31] studied that pinching of tomatoes promoted plant growth, total yield and quality fruit production.

Days to maturity
The data on days to maturity is presented in (Table 2). Its statistical analysis showed that sowing dates and umbel pinching had significant effect on days to maturity while their interaction was found non-significant. Mean data of sowing dates showed that sowing dates had significant effect on days to maturity. Maximum days to maturity (151 days) were observed at 25 th October whereas minimum days to maturity (102.4 days) were noted at 24 th November. Mean data of umbel pinching showed that days to maturity were significantly affected by umbel pinching. Maximum days to maturity (137.4 days) were observed in case of pinching PTQ umbels whereas minimum days to maturity (129.9 days) were recorded in case of control. When planting is done earlier, plants receive comparatively high temperature and long day length which might extend vegetative growth period ultimately resulted in delayed seed maturity while, in delayed planting due to short day length and low temperature result in early seed maturity [20]. Maximum days taken to flowering and seed maturity in pinched plant were due to the formation of mature shoots for bearing flowers which took more days. More number of days required to bud appearance due to pinching were observed in Chrysanthemum by [32][33][34]. [25] also reported that pinched flowers needed maximum days to start reproductive growth and hence delayed in seed maturity in chrysanthemum.

Variability in harvest time
The data regarding variability in harvest time is presented in figure I. Statistical analysis indicates that sowing dates, umbel pinching and their interaction had significant effect on variability in harvest time. The interaction between sowing dates and umbel pinching (Fig. 1) indicated that maximum (36.6 days) variability in harvest time was recorded at 25 th October sowing with pinching TQ whereas the minimum (25.7 days) variability in harvest time was observed at sowing on 24 th November in case of control. Variability in harvest time may be due to variability in seed maturity. Due to early planting, plants received high temperature and long day length which might have extended vegetative growth period ultimately resulted in delayed seed maturity while, in delayed planting due to short day length and low temperature result in early seed maturity [20]. The reason of greater variability in harvest time might be due to the fact that primary umbel matures first because it appears first and located on the top of the flowering stock. The removal of tertiary and quaternary inflorescence diverted the Photosynthate towards the primary and secondary inflorescence which increases their vegetative growth and the umbels remain green for longer time period. Our findings are in line with [35] who obtained similar results in training carrot.

Seed yield umbel -1 (g)
The data regarding seed yield umbel -1 is presented in figure 2. Statistical analysis indicated that sowing dates and umbel pinching had significant effect on seed yield umbel -1 and their interaction was also found significant. The interaction between sowing dates and umbel pinching (Fig. 2) indicated that highest seed yield umbel -1 (6.9 g) was noted at 25 th October sowing in pinching STQ whereas the lowest seed yield umbel -1 (2.2 g) was recorded at 24 th November sowing date with pinching PTQ umbels. At early planting seed yield was found maximum because of high light intensity, temperature and long day length preparing more photosynthesis for the plant which add toward more seed yield. Favorable atmospheric conditions could have also promoted vegetative and reproductive growth such as less flower abortion, optimum temperature, efficient pollinators and nutrients availability for all florets in the umbel [36]. Our findings agreed with that of [29] reported that yield of different varieties of onion is influenced by delay in planting. On the other hand, Pinching STQ umbels resulted in maximum seed yield umbel -1 . This might be due to the fact that through umbel pinching nutrients and hormones are diverted towards the remaining umbels. Because of pinching the umbels face less competition for nutrients and hormones. More nutrients and hormones are transported to the flowers and they produce bigger, heavier and healthy seeds. Our results are in line with [37] who reported that higher umbel size, number of flower umbel -1 , number of seeds/umbel and highest quality of seed was exhibited in only primary umbels.

Seed yield plant -1 (g)
The data regarding seed yield plant -1 is presented in figure III. Statistical analysis showed that sowing dates, umbel pinching and their interaction had significant effect on seed yield plant -1 . The interaction between sowing dates and umbel pinching (Fig. 3)

Seed yield (t ha -1 )
The data regarding seed yield (t ha -1 ) is shown in (Fig. 4. Statistical analysis indicated that sowing dates and umbel pinching had significant effect on seed yield t ha -1 and their interaction was also found significant. The interaction between sowing dates and umbel pinching (Fig. 4) indicated that maximum seed yield (5.4 t ha -1 ) was found on 25 th October sowing with pinching of TQ umbel. While minimum seed yield (1.6 t ha -1 ) was noted in case of 24 th November sowing with pinching of STQ umbel. Maximum seed yield (t ha -1 ) was observed at early planting which might be due highest seed yield per umbel and seed yield plant -1 . Other reason could be the combined contribution of the yield contributing characters affected by comparatively lower atmospheric temperature and short day length. On the other hand, slow vegetative and reproductive growth and minimum yield were observed at late planting because of high temperature and long day length. These findings coincided with that of [39] concluded that seed yield of onion cultivars was maximum due to early sowing. Due to umbel pinching, nutrients and hormones are balanced and influenced as a result the existing umbels which face less competition for nutrients and hormones. More nutrients and hormones are transported to the existing umbels which produce bigger, heavier and healthier seeds and have higher germination percentage and vigor index. Seeds become more vigorous and viable. Pinching gathers additional photosynthates which are used for more flowers production. Pinching checked apical dominance and diverted extra energy in to the production of more numbers of branches, flowers and seeds [28].

Conclusion
It is concluded that among different sowing dates, sowing on 25 th October provided increased seed yield of carrot. Pinching of TQ (tertiary and quaternary) umbels of carrot improved seed production and its quality. Therefore, carrot should be sown on 25 th October and pinched its TQ (tertiary + quaternary) umbels for the improved seed production.