Effect of sowing dates and late season water deficit stress on quantitative and qualitative traits of canola cultivars

Abstract

To investigate the effects of sowing dates and late season water deficit stress on quantitative and qualitative traits of different canola cultivars, a 2-year field experiment was carried out in the 2014–2015 and 2015–2016 growing seasons. The experimental factors consisted of sowing date at two levels (7th and 27th October), irrigation at two levels (full irrigation and irrigation termination at silique formation stage) and four German canola cultivars including Trapper, Makro, Smilla, and Agamax. The results indicated that the main effects of sowing date, irrigation, and cultivar were significant on all studied characteristics except for harvest index. The interaction between sowing date and irrigation was also statistically significant on silique number per plant, oil percentage, linolenic acid, and erucic acid percentage. The results demonstrated that seed yield and its components oil percentage and oil yield, as well as oleic and linoleic acid percentage, decreased when sowing date was delayed until 27th October. Due to irrigation termination, all the studied traits decreased except for linolenic and erucic acid. Seed yield also decreased. The results suggest that to improve seed and oil yield, canola should be sown on 7th October and fully irrigated until physiological maturity stage in the study area.

Keywords

canola fatty acids composition new cultivation status late-season drought stress

Introduction

Improvement of seed yield in canola (Brassica napus L.) has been the primary objective of canola breeders for many years. Grain yield is a quantitative characteristic, which is highly influenced by the environment and has a low heritability. All the biotic and abiotic stresses are the common factors, which reduce production. Drought stress is the most important factor limiting crops yield in agricultural systems especially in arid and semi-arid regions. Thus, drought indices, which provide a scale of stress based on loss of yield under nonstress conditions in comparison to normal conditions, have been used for screening drought-tolerant genotypes (Mitra, 2001). A slight decrease in the accessibility of water to a growing plant immediately reduces its metabolic and physiological functions. The extensive production of reactive oxygen species (ROS) and their roll in cell damage induced by water deficit is well known. Water stress caused a significant decrease in chlorophyll content by activating the chlorophyllase enzyme to reduce the adverse effect of ROS. To neutralize the impact of ROS, plants have evolved a number of protective defense mechanisms such as enzymes and nonenzymatic antioxidants. Of these, free proline accumulation at high concentration has been shown to have an adaptive mechanism of stress tolerance. Proline is an osmo-regulator, acting by maintaining membrane integrity and affecting the solubility of various proteins due to its interaction with hydrophobic residues on the protein surface under water shortage. The yield and yield components of a plant mainly depend on growth conditions, which are significantly affected by water availability. The greatest impact of water deficit is observed when the stress happens during the flowering period or pod-filling stages. At reproductive phase, water stress advances the process of flower and pod drop and decreased seed yield (Sinaki, et al. 2007). Several studies on rapeseed demonstrated that appropriate irrigation along with supplementary water for plants during the flowering period increased seed number per pod due to the expanded leaf area and chlorophyll content leading to higher photoassimilate supply (Anjum et al., 2011; Poulson et al., 2002). Some other studies showed that due to continued development of plants under stress conditions, seed formation and filling period had extensive overlapping time courses (Safavi Fard et al., 2018). Changes in environmental parameters may influence the quality of canola seed oil through improving ontogenesis. Notably, the interaction of environmental conditions and genotype also influences the quality of canola fatty acid composition (Gunasekera et al., 2006). In general, seed yield has been found to decrease with a delay in sowing date (Safavi Fard et al., 2018). Also, Uzun et al. (2009) reported that oil percentage reduced by 3% per month of sowing delay. Pritchard et al. (2000) concluded that water deficit stress changed the ratio of oleic to linoleic acid due to a decrease in the content of oleic acid. Changing the sowing date can affect the plant growth and development phase. Sowing date is necessary for establishing a seedling that has sufficient growth for good winter hardiness. Planting delay leads to decrease winter survival due to insufficient growth (Safavi Fard et al., 2018). The seed yield and maturity of canola are highly influenced by sowing date (Ozer, 2003). In this regard, it has been reported that with delayed sowing date, seed yield and straw yields were lower than with early planting (Birun Ara et al., 2011). According to these points and due to the significance of canola as an edible plant with vegetable oils, this study investigates the most appropriate genotypes and planting dates with regard to climatic conditions.

Materials and methods

Study site and experimental design

To evaluate the effects of sowing dates and late season water deficit stress imposed by irrigation termination on quantitative and qualitative traits of different canola cultivars, a 2-year field experiment was carried out at the Seed and Plant Improvement Institute, Karaj, Iran (35′ and 59°E and of 50′ and 75°N). The experiment was laid out as a factorial split plot in a randomized complete block design with three replicates during the 2014–2015 and 2015–2016 growing seasons. The study site has an average annual rainfall of 243 mm distributed throughout the year. The meteorological characteristics of the study region are given in Table 1. The experimental design consisted of three factors; sowing date at two levels (7th and 27th October), irrigation at two levels (full irrigation and irrigation termination at silique formation stage), which were randomized on the main plots and four German canola cultivars including Trapper, Makro, Smilla and Agamax, which were randomized in the subplots.

Table 1.

The meteorological characteristics of the study region.

Months	October	November	December	January	February	March	April	May	June	July
2014–2015
MAT (°C)	18.2	10.4	4.2	−2	3.2	6.1	11.6	15.8	23.8	27.2
Rain (mm)	11.2	52.1	68.1	81.4	71.2	68.6	56.4	46.1	1.2	0.0
2015–2016
MAT (°C)	17.7	11	3.7	−2.5	−2.2	5.8	9.6	14.2	21.2	25.2
Rain (mm)	38.6	41.7	55.4	48.2	79.6	52.1	42.3	35.2	0.0	0.0
2005–2014
MAT (°C)	17.3	10.5	4.9	1.3	0.9	5.2	10.7	15.2	21.2	26.6
MR (mm)	11.9	59.5	73.5	72.4	79	81.6	64	34.3	2.1	0.6

MAT: mean air temperature; MR: mean rain.

Field preparation and plots establishment

The field was fallow the previous year and the previous crops was barley (Hordeum vulgare L.) in 2013–2014. One week before sowing, the soil samples were taken from 15 to 30 and 30 to 60 cm depths, air-dried, crushed, and passed through a 2 mm riddle to determine the soil properties. Soil EC and pH were determined in 1:2 soil:water suspension. The soil texture is a sandy loam. Soil chemical properties from a sample taken before planting are listed in Table 2. In autumn, the seedbed was prepared using the semideep plough to a 25 cm depth followed by disk and furrowed. The experimental plots were established so that each plot consisted of 6 rows, 6 m long with 30 cm spaced between rows and 5 cm distance between plants on the rows. According to soil physicochemical analysis results and recommendations, phosphorus at the rate of 60 kg ha⁻¹ in the form of triple superphosphate and potassium at the rate of 20 kg ha⁻¹ in the form of potassium sulfate were applied before seed sowing while nitrogen fertilizer at the rate of 150 kg ha⁻¹ in the form urea was applied at three different stages; one-third before seed sowing and mixed into the soil, one-third at stem elongation stage, and one-third at flowering stage by spreading the fertilizer onto the soil surface just before irrigation.

Table 2.

Physicochemical properties of soil collected from study site.

Depth (cm)	EC (ds/m)	pH	Organic carbon (%)	N (%)	P (ppm)	K (ppm)	Texture
0–30	1.45	7.9	0.91	0.09	14.7	197	Clay loam
30–60	1.24	7.2	0.99	0.07	15.8	155	Clay loam

Seed sowing and irrigation termination

Canola seeds were disinfected with fungicide carboxin thiram (2:1000) and manually sown on 7th and 27th October at a depth of 3 cm. After seed sowing, the plots were irrigated immediately with a drip irrigation system to avoid wilting at during the plant growth. The plots were thinned after complete seedling establishment, keeping distances on the row at about 5 cm. The experimental plots were kept free of weeds by hand pulling and hoeing throughout the growing seasons. During the growing season, irrigation was performed equally after 60 mm evaporation from a class A evaporation pan. At silique formation stage, irrigation was terminated in half of the plots until physiological maturity stage.

Data collection

Agronomic traits

The final harvest was performed by harvesting the four middle rows at physiological maturity when 50% of the seeds in the main siliques and primary branches turned brown (Ozer, 2003). To estimate biological yield, samples were oven dried at 70°C for 72 h. Then dry weight was measured using a digital scale. Furthermore, silique number per plant, seed number per silique, 1000-seed weight and final seed yield, as well as harvest index, were determined. About 1000-seed weight was determined by measuring the weight of four random samples after counting the seeds using a laboratory seed counter.

Oil content and fatty acid composition

Oil percentage was measured by an Inframatic 8620 Percor, Germany. Oil yield was obtained by multiplying seed yield by oil percentage. Seed oil extraction and fatty acid composition determination were carried out using a Soxhlet apparatus and the gas chromatography method, respectively. The extraction of 250 g of powdered seeds was performed using diethyl ether and petroleum spirit, respectively, at 450°C for 6 h. Solvent was removed from the oil under reduced temperature, pressure, and refluxing at 70°C. The obtained oil was stored in a freezer for subsequent analysis. Fatty acid composition, including unsaturated (oleic acid (C18:1), linoleic acid (C18:2) and linolenic acid (C18:3), and erucic acid (C 22:1)) fatty acids, was analyzed using gas chromatography of methyl esters (Lee et al., 1998) by the following procedure. Fifty milligram of extracted oil was saponified with 5 ml of methanolic NaOH (2%) solution by refluxing for 10 min at 90°C. Afterward 2.2 ml BF3-methanolic was added, then the samples were boiled for 5 min. The fatty acid methyl esters (FAMEs) were extracted from a salt-saturated mixture with hexane. The FAMEs were then analyzed using a gas chromatograph (UNICAM model 4600; Cambridge, UK) coupled with an flame ionization detector (FID). The column used for fatty acid separation was a fused silica BPX70 column, 30 m × 0.22 mm i.d. × 25 µm film thickness (from SGE, UK). The oven temperature was held at 180°C during separation; the injector and detector temperatures were 240 and 280°C, respectively. The carrier gas (helium) flow ratio was 1 ml min⁻¹. One microliter of methyl esters of free fatty acids was injected into the split injector. The ratio was adjusted to 1:10. The compounds were identified by comparison of their retention times with authentic compounds. The internal standard C15:0 was used in the quantitative analysis of the separated fatty acids. Each fatty acid was expressed as a percent of the total fatty acids.

Data analysis

The data were analyzed using the general linear model procedure of the statistical analysis system, SAS. When analysis of variance showed significant treatment effects, Duncan’s multiple range test was applied to compare the means at p < 0.05.

Results

Combined analysis of variance on the data showed that the effect of year was significant on all agronomic traits except for biological yield and linoleic acid (Table 3). In addition, analysis of variance indicated that the main effects of sowing date, irrigation, and cultivar were significant on all studied characteristics except for harvest index (Table 3). The interaction between sowing date and irrigation was also statistically significant on silique number per plant, oil percentage, linolenic acid, and erucic acid percentage, but all other two-way and three-way interactions were not significant (Table 3). Yield and yield components, harvest index, and oil percentage, as well as oil yield, oleic acid, and erucic acid percentage, were higher in the first year compared with the second year (Table 4), which might be attributed to better growing conditions in the first year. The main effects of sowing time and irrigation treatment are shown in Table 5. Seed yield and its components (including silique number, seed number per silique, and 1000-seed weight), biological yield, oil percentage, and oil yield, as well as oleic and linoleic acid percentage, decreased when sowing date was delayed after 27th October. However, linolenic and the erucic acid percentage increased (by 23.30% and 48.74%, respectively) with the delay in sowing date (Table 5). Late sowing date decreased seed and oil yield by 59.14% and 55.90%, respectively. Similar results were obtained when irrigation was terminated at silique formation stages. All the studied traits showed a reduction, but linolenic and erucic acid increased by 13.21% and 25.50%, respectively (Table 5). Seed yield decreased by 76.79% due to irrigation termination at silique formation stage (Table 5). In the case of canola cultivars, there was no significant difference between Trapper and Agamax. These cultivars produced the maximum silique number per plant, seed number per silique, and 1000-seed weight as well as seed yield, biological yield, oil percentage, oil yield, oleic acid, and linoleic acid content (Table 5). The maximum linolenic and erucic acid were found in Smilla. There was no significant difference between Smilla and Makro regarding linolenic acid percentage (Table 5). Smilla showed the minimum values for yield components (Table 5). Smilla and Makro had the minimum seed yield (Table 5). Furthermore, no significant difference was found between Smilla and Makro regarding oil percentage, oil yield, and linolenic acid percentage. Trapper and Agamax had the minimum erucic acid percentage. Significant interactions between sowing date and irrigation are shown in Table 6. The maximum silique number per plant was obtained when seed sowing was performed on 7th October and plants were fully irrigated (Table 6). By contrast, the minimum silique number per plant was shown by those plants which were sown on 27th October and experienced irrigation withholding at silique formation stage (Table 6). In general, silique number per plant decreased with the delay in seed sowing and water limitation during silique formation stages. A similar trend was observed in the case of oil percentage. The maximum and minimum oil percentage were shown by seed sowing on 7th October along with full irrigation treatment and seed sowing on 27th October accompanied with irrigation termination at silique formation stage, respectively (Table 6). The results revealed that the maximum linolenic and erucic acid were shown by those plants sown on 27th October with irrigation withholding at silique formation stage (Table 6).

Table 3.

Analysis of variance on some agronomic traits and fatty acid composition as affected by sowing date, irrigation termination, and cultivar.

Sources of variation	df	Silique number	Seed number per silique	1000-Seed weight	Seed yield	Biological yield	Harvest index
Year	1	4085.955^a	167.482^a	3.390^a	4943606.510^a	12394125.375	123.556^a
Error	4	22.061	1.216	0.045	41178.167	2068394.115	5.681
Sowing date	1	116016.367 ^a	3685.282^a	72.593^a	77154583.010^a	1259267988.167^a	0.626
Year × sowing date	1	196.940^b	12.907^b	0.022	185416.260	359905.042	51.115^b
Irrigation	1	28088.463^a	799.260^a	16.650^a	20165750.010^a	292916001.042^a	6.896
Year × irrigation	1	25.938	0.070	0.064	12719.010	1067660.167	2.211
Sowing date × irrigation	1	495.496^a	1.084	0.025	479261.344	4591125.375	0.012
Year × sowing date × irrigation	1	39.398	4.770	0.250	445946.344	388621.500	7.299
Error	12	30.122	1.756	0.063	441960.028	2248405.934	8.886
Cultivar	3	3947.554^a	112.780^a	2.324^a	2703047.872^a	40439937.194^a	1.933
Year × cultivar	3	1.031	0.154	0.011	7351.455	67331.292	0.051
Sowing date × cultivar	3	58.185	1.002	0.018	65013.344	653201.972	0.434
Year × sowing date × cultivar	3	0.571	0.752	0.019	43522.427	23303.514	1.792
Irrigation × cultivar	3	5.865	0.134	0.034	19380.455	919948.292	0.869
Year × irrigation × cultivar	3	10.543	0.461	0.000	9428.288	241650.528	0.515
Sowing date × irrigation × cultivar	3	2.247	1.067	0.006	1044.788	509681.514	1.480
Year × sowing date × irrigation × cultivar	3	2.666	0.071	0.003	4311.399	2385.861	1.039
Error	48	34.421	2.414	0.047	334691.451	933331.646	31.276
Coefficient of variation	%	4.12	9.27	6.03	16.56	6.68	23.14
Sources of variation	df	Oil percentage	Oil yield	Oleic acid	Linolenic acid	Linoleic acid	Erucic acid
Year	1	4.563^b	768805.010^a	9.399^a	3.651^a	7.686	81.034^b
Error	4	0.394	9398.167	0.007	0.140	1.205	7.960
Sowing date	1	145.214^a	18274512.760^a	42.527^a	58.272^a	192.047^a	9087.041^a
Year × sowing date	1	4.660^a	66834.260	1.244^a	1.684	1.746	0.482
Irrigation	1	31.133^a	4762840.510^a	13.677^a	16.499^a	37.000^a	1846.260^a
Year × irrigation	1	1.213^b	75.260	0.065	0.019	0.004	2.870
Sowing date × irrigation	1	1.318^b	204149.260	0.000	2.057^b	0.278	70.727^a
Year × sowing date × irrigation	1	0.259	83957.510	1.110	0.083	0.527	0.282
Error	12	0.190	96289.083	0.016	0.426	0.783	4.103
Cultivar	3	4.680^a	636640.177^a	1.988^a	1.972^a	5.273^a	304.394^a
Year × cultivar	3	0.224	486.344	0.005	0.015	0.009	0.193
Sowing date × cultivar	3	0.137	24999.205	0.079	0.306	0.104	15.094
Year × sowing date × cultivar	3	0.031	9075.372	0.055	0.032	0.099	0.268
Irrigation × cultivar	3	0.024	1548.899	0.058	0.014	0.026	0.663
Year × irrigation × cultivar	3	0.008	2263.538	0.157	0.027	0.051	0.526
Sowing date × irrigation × cultivar	3	0.003	283.094	0.103	0.027	0.155	1.917
Year × sowing date × irrigation × cultivar	3	0.021	606.677	0.003	0.034	0.211	1.170
Error	48	0.284	63474.507	0.045	0.216	0.572	12.608
Coefficient of variation	%	1.22	16.32	0.33	7.92	4.61	11.79

ns: not significant.

^a p < 0.01.

^b p <0.05.

Table 4.

Main effect of year on some agronomic traits and fatty acid composition of canola cultivars.^a

Year	Silique number	Seed number per silique	1000-Seed weight (g)	Seed yield (kg ha⁻¹)	Harvest index (%)	Oil percentage	Oil yield (kg ha⁻¹)	Oleic acid (%)	Linolenic acid (%)	Erucic acid (%)
2014–2015	148.76a	18.08a	3.79a	3720.1a	25.30a	44.00a	1633.42a	64.52a	5.67b	0.31a
2015–2016	135.71b	15.44b	3.41b	3266.3b	23.03b	43.56b	1454.44b	63.89b	6.06a	0.29b

^a Columns with the same letter are not significantly different at the 5% level of probability.

Table 5.

Main effect of sowing date, irrigation and cultivar on some agronomic traits and fatty acid composition of canola cultivars.^a

Factors	Levels	Silique number	Seed number per silique	1000-Seed weight (g)	Seed yield (kg ha⁻¹)	Biological yield(kg ha⁻¹)	Oil percentage	Oil yield (kg ha⁻¹)	Oleic acid (%)	Linolenic acid (%)	Linoleic acid (%)	Erucic acid (%)
Sowing date	7th October	177.0a	22.96a	4.47a	4389a	18085a	45.01a	1980a	64.87a	5.10b	17.82a	0.204b
Sowing date	27th October	107.4b	10.57b	2.73b	2596b	10842b	42.55b	1107b	63.54b	6.65a	15.00b	0.398a
Irrigation	Full irrigation	159.3a	19.65a	4.02a	3951a	16210a	44.35a	1766a	64.58a	5.45b	17.02a	0.257b
Irrigation	Until seed setting	125.3b	13.88b	3.18b	3034b	12717b	43.21b	1321b	63.83b	6.28a	15.78b	0.345a
Cultivar	Trapper	153.0a	18.54a	3.860a	3766a	15540a	44.13a	1675a	64.44a	5.621b	16.80a	0.271c
	Makro	136.0b	15.78b	3.453b	3323b	13760b	43.56b	1461b	64.07b	6.022a	16.17b	0.319b
	Smilla	127.2c	14.18c	3.240c	3103b	12990c	43.27b	1355b	63.87c	6.204a	15.86b	0.343a
	Agamax	152.8a	18.57a	3.868a	3780a	15570a	44.17a	1685a	64.46a	5.646b	16.80a	0.272c

^a Columns with the same letter are not significantly different at the 5% level of probability.

Table 6.

Interaction between sowing date and irrigation on silique number, oil percentage, linolenic acid, and erucic acid.^a

Sowing date	Irrigation	Silique number	Oil percentage	Linolenic acid (%)	Erucic acid (%)
7th October	Full irrigation	196.4a	45.70a	4.826d	0.17d
7th October	Until silique formation	157.6b	44.33b	5.363c	0.24c
27th October	Full irrigation	122.3c	43.00c	6.092b	0.35b
27th October	Until silique formation	92.65d	42.10d	7.213a	0.45a

^a Columns with the same letter are not significantly different at the 5% level of probability.

Discussion

The current experiment indicated that late sowing reduces canola seed yield and yield components. Generally, final seed yield is a function of all the yield components. Yield components of canola, like silique per plant, seed number per silique, and 1000-seed weight were significantly affected by the sowing dates. This reduction might be due to variation in temperatures in late seed sowing. In a similar study, Turhan et al. (2011) have stated that sowing date significantly affects canola growth and final seed yield through affecting the number of days to flowering and flowering duration. The same results have been reported by other researchers (Uzun et al., 2009) who mentioned that late sowing date causes delayed flowering time and reduces final seed yield. On the other hand, the increase in final seed yield as a result of early or optimum seed sowing date may be attributed to more light (long growing season, due to earlier seed sowing, increases incoming radiation), water and mineral absorption by plants, which in turn lead to increased photosynthesis and assimilate production. It has been reported that late sowing date not only decreases crop growing period but also causes poor pollination and silique/seed setting at the end of the season due to hot and dry days (Faraji et al., 2008). Late sowing date increases the risk of late season heat and drought stress, when plants are at their critical reproductive period. Higher temperature has been shown to cause abortion of flowers in several species, including pea (Pisum sativum L.) (Guilioni et al., 1997), sunflower (Helianthus annuus L.) (Chimenti and Hall, 2001), and canola (Angadi et al., 2000; Morrison and Stewart, 2002). According to the results, biological yield was higher in early sowing date treatment than in the late sowing date treatment and this might be because of the increase in plant dry weight (Fathi et al., 2003). The crop sown on 7th October produced significantly higher oil yield as compared to the crop sown on 27th October, probably due to higher temperatures during seed filling, which may also have contributed to the smaller seed size observed for this sowing date. Reduction in oil percentage in developing canola seeds before full maturity as a result of late sowing date has been reported by Bhardwaj and Hamama (2003). The fatty acids biosynthesis during seed development is affected by the environmental conditions (Hassan et al., 2005). Moreover, it has been reported that soil organic matter and microbial activity have positive effects on fatty acid composition (Khosro et al., 2011). Although canola is bred for zero erucic acid, a small amount of erucic acid was observed in this study mostly due to the late sowing date. Irrigation termination at silique formation stage until seed maturity drastically decreased seed yield and its components. Abiotic stress at the later stages of reproductive growth can result in source limitation for seed yield by inducing leaves shedding and hastening maturity (Gan et al., 2004). Seed number per silique was the most sensitive yield component to irrigation withholding at silique formation stage. Similar results have been reported by Diepenbrock (2000). It appears that irrigation termination caused yield reduction probably more by inducing seed abortion via limiting photosynthesis. In addition, as water shortage during reproductive stages affects sink capacity, it can decrease seed weight. Thus, it seems that irrigation termination during this period reduced seed yield via reduction of seed weight, seed number per pod, and silique number per plant. Champolivier and Merrin (1996) found that yield and yield components of canola were mainly affected by water shortage occurring from flowering to the end of seed setting period. The highest biological yield was obtained when full irrigation was applied during growing season. Gunasekara et al. (2006) observed a significant reduction in biological yield due to water shortage during reproductive growth compared to the control. Deepak and Watal (2000) have observed a reduction in biological yield and dry matter in two canola cultivars, grown under water deficit conditions. Under water shortage conditions, the oil percentage and percentage of oleic and linoleic acid decreased, what could be explained by a shorter growing season. Researchers have stated reduced availability of carbohydrates for oil biosynthesis under water shortage conditions. For instance, Bouchereau et al. (1996) showed that water stress at flowering stage, affects oil content, and fatty acid composition in canola seeds. Nasri et al. (2008) also reported water shortage could decrease seed oil content of five canola cultivars. Furthermore, Singh and Sinha (2005) stated that the reduction in oil content might be due to the oxidation of some polyunsaturated fatty acids. In this study, water limitation resulted in increased seed linolenic acid and erucic acid but decreased linoleic acid and oleic acid content, which is consistent with earlier reported studies (Singer et al., 2016). Differences in seed yield and yield components of canola cultivars were also significant. Generally, Trapper and Agamax had higher seed yield and yield components than other cultivars under similar conditions. These results support the findings of Rabiee et al. (2004) who have shown that even different cultivars of the same species had different yield potentials. In addition, canola cultivars showed different fatty acid profiles, these results agree with the findings of Turhan et al. (2011). canola.

Conclusion

It was concluded from present experiment that canola sown on 7th October and treated with full irrigation produced the maximum seed yield sand yield components as well as oil yield, oleic acid, and linoleic acid. The results demonstrated that only 20 days of delay in seed sowing could decrease seed yield by about 60% in different canola cultivars. Moreover, irrigation termination at silique formation stage could reduce final seed yield by about 77%. Therefore, it is recommended that to improve yield and yield components and oil quality, canola should be sown on 7th October and fully irrigated until physiological maturity stage under the conditions of the current study area.

Footnotes

Author’s note

Parisa Nazeri and Mojtaba Mirakhori are members of young researcher club.

Acknowledgements

I would also like to extend my thanks to Azad University for its support.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

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