Seed number in canola (Brassica napus L.): Effects of dry matter, crop growth rate, temperature, and photothermal quotient around flowering

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1 International Research Journal of Applied and Basic Sciences 2014 Available online at ISSN X / Vol, 8 (12): Science Explorer Publications Seed number in canola (Brassica napus L.): Effects of dry matter, crop growth rate, temperature, and photothermal quotient around flowering Abolfazl Faraji Associated professor, Agricultural and Natural Resources Research Center of Golestan, Postal code , Beheshti Street, Gorgan, Iran. Corresponding Author : Abolfazl Faraji ABSTRACT: Seed number is a function of dry matter accumulation, crop growth rate (CGR), photothermal quotient (PTQ) and temperature during a critical developmental period, which is around flowering in canola (Brassica napus L.). The objective of this experiment was to determine factors such as dry matter, CGR, temperature, and PTQ around flowering which affect seed number. The experiment was conducted at Agricultural Research Station of Gonbad, Iran, between 2005 and Two cultivars of canola (Hyola401 and RGS003), as subplots were grown at 5 sowing dates as main plots, spaced approximately 30 days apart, to obtain different environmental conditions during flowering. The experiment was arranged in two conditions, i.e., supplemental irrigation and rainfed. Seed number per unit area was a key factor for increasing seed yield. Late sowing dates made the critical period of flowering coincide with high temperatures, decreased days to the flowering, seed number per unit area and seed yield. Seed number was driven by the availability of carbohydrates around flowering. Seed number per unit area was maximized for the cultivars when exposed to the highest PTQ, and to the lowest temperature between the beginning of flowering to that of seed filling. The relationship of seed number with aboveground dry matter, CGR, temperature, and PTQ around flowering, over different environmental conditions, showed these variables were generally applicable to seed number determination. Keywords: Flowering; Cultivar; Seed filling; Environmental conditions; Seed yield. INTRODUCTION Seed number per unit land area is the main seed yield component in most annual crops (Egli, 1998; Kantolic and Slafer, 2001; Poggio et al., 2005; Sinclair and Jamieson, 2006). Canola yield can be increased with increase in seed number per unit land area (Morison, 1993; Brandt and McGregor, 1997; Angadi et al., 2000; Gan et al., 2004), so identifying factors that determine seed number is of great importance. A great proportion of the variation in seed number are related to environmental conditions during the critical period when seed number is being determined (Cantagallo et al., 1997; Andrade et al., 1999), i.e., flowering stage in canola. Gan et al. (2004) proposed that flowering period is the critical window for seed number determination, probably due to vulnerability during pollen development, anthesis and fertilization (Hall, 1992). Pechan (1988) reported that failure of fertilization was the major factor limiting seed number per pod in canola. During the critical window, seed number exhibit a negative response to temperature (Ortiz-Monasterio et al., 1994; Bindraban et al., 1998; Angadi et al., 1999; Angadi et al., 2000; Morrison and Stewart, 2002) and a positive response to water availability (Brandt and McGregor, 1997; Johnston et al., 2002) and to radiation intercepted by the crop (Kiniry and Ritchie, 1985). Therefore, crop specific photothermal quotient (PTQ) has been developed to synthesize the opposite effects of radiation and temperature on seed number in different species (Fischer, 1985; Cantagallo et al., 1997; Chimenti and Hall, 2001). The importance of cultivar, sowing date, temperature and water stress on the number of pods and seeds per pod have been investigated in canola (Nielsen, 1997; Chongo and McVetty, 2001; Morrison and Stewart, 2002; Gan et al., 2004), but there have been no detailed studies involving the effects of dry matter, CGR, and PTQ at the critical developmental period of flowering. Therefore, as part of a broader project, we investigated the effects of

2 aboveground dry matter, CGR, temperature, and PTQ around flowering on seed number, under a wide range of environmental conditions. MATERIALS AND METHODS Experiment 1 (Rainfed conditions) The experiment was conducted at Agricultural Research Station of Gonbad, Golestan province, Iran (45 m a.s.l., 37 o N, 55 o E) over two years ( and ). The region is classified as warm and semiarid Mediterranean climate. The soil was a fine, silty, mixed, thermic typic Calcixerol. Prior to sowing, soil samples were taken, and according to soil test data, P and K were preplant-incorporated to supply 50 kg P 2 O 5 ha -1 and 50 kg K 2 O ha -1 from triple super phosphate and potassium sulphate, respectively. N was applied at 75 kg ha -1 in the form of urea, that a third of this amount was applied preplant, a third of that was side-dressed at beginning of stem elongation and the rest at the beginning of flowering. The experiment was a randomized complete block design arranged in split plot with 3 replications. Two cultivars of spring canola (Hyola401, a hybrid cultivar and RGS003, an open pollinated one) as subplots were grown at five sowing dates as main plots. The sowing dates were 9 Nov., 6 Dec., 5 Jan., 4 Feb. and 6 Mar. in , and 6 Nov., 6 Dec., 5 Jan., 4 Feb. and 6 Mar in The best sowing date for canola in the area is mid-nov., but the sowing dates were selected to have a wide range of environmental conditions and assimilate availability around flowering. Plots were over planted and after seedling establishment, the plants were thinned to the desired spacing between plants of 5 cm ( plant ha -1 ). Each subplot consisted of eight 5-m long rows. Main plots and subplots were 2 and 0.4 m apart, respectively. A 3-m pathway separated replicates. In each plot, aboveground dry matter samples were taken from 10-plants of rows of two and three. At physiological maturity 10-plant samples were obtained from each plot to determine number of pods per plant and seeds per pod. At harvested time (2 days after physiological maturity) rows of 5, 6 and 7 were harvested for seed yield determination. During the season, phenological stages were recorded with the Harper and Berkenkamp (1975) growth stage key. Seed number per unit area was calculated as plant number per unit area pod number per plant seed number per pod. Maximum and minimum temperatures, rainfall and radiation measured at a near-by weather station (Table 1). Mean temperatures were calculated for the same growth phases as the sum of the daily temperatures divided by the number of days during the growth phase. PTQ was calculated as the ratio of mean daily incident radiation to mean daily temperature in excess of 0 0 C (Adamsen and Coffelt, 2005; Poggio et al., 2005), from the beginning of flowering to that of seed filling. Aboveground dry matter, temperature, CGR, and PTQ have all been correlated to seed number, and significant relations (Table 2) were used (SAS, 1996). Because there was no significant difference between irrigation conditions with respect to the coefficients of the linear function, data of irrigation conditions were pooled, so linear function fitted to the data of each cultivar. Data were tested by analysis of variance using Statistical Analysis System (SAS Institute, 1996). Experiment 2 (Supplemental irrigation) In second experiment, the treatments and measurements were the same as in the first one, but the plants were irrigated 3 times, 5 days after the beginning of stem elongation, 5 days after that of flowering, and 5 days after that of seed filling stages, to replenish soil water in the root zone to field capacity. The objective of this experiment was to supply adequate water amount for canola, and to have a condition without water stress during the crop growth season. Two days before irrigation times, soil samples were dried for 24 hours at C, and weighed. Then soil water content was measured, and the plots were reached to field capacity with irrigation, using a flow meter to measure the amount of water applied (Zhang et al., 1999). RESULTS Aboveground dry matter at the beginning of flowering showed significant relationship with seed number for the cultivars, explaining 87 and 82% of the variation for Hyola401 and RGS003, respectively (Fig. 1, Table 2), explained a greater proportion of the variation of the data in Hyola401 than RGS003. There were significant (P=0.05) differences for seed yield, pod number per plant and seed number per pod at the beginning of flowering between crops grown at different moisture regimes (Table 3). In both years, the mean pod number per plant and seed number per pod at supplemental irrigation conditions were more than those of rainfed conditions (Table 3), due to adequate water supply, and a condition without water stress during the crop growth season. The mean pod number per plant under supplemental irrigation and rainfed conditions was 63.5 and 50.3 in , and 65.4 and 2169

3 54.6 in , respectively (Table 3). Also, the mean seed number per pod under supplemental irrigation and rainfed conditions was 19.3 and 17.1 in , and 12.8 and 11.0 in , respectively (Table 3). The relationship between seed number and CGR from the beginning of flowering to that of seed filling explained 88 and 80% of the variation for Hyola401 and RGS003, respectively (Fig. 2, Table 2), showing a greater proportion of the variation of the data in Hyola401 than RGS003. The slop of this relationship was more in Hyola401 than RGS003 (9869 and 7679 for Hyola401 and RGS003, respectively) (Fig. 2, Table 2), showing the greater response of Hyola401 than RGS003 to CGR from the beginning of flowering to that of seed filling. The variation in seed yield was closely associated with the variation in seed number per unit area (Table 3 and 4), which in turn was associated with aboveground dry matter at the beginning of flowering, and CGR, mean air temperature, and PTQ from the beginning of flowering to that of seed filling (Figs. 1, 2, 3 and 4). The response of cultivars differed in aboveground dry matter at the beginning of flowering, pod number per plant, seed number per pod, and seed yield (Table 4). In both years, pod number per plant, seed number per pod, and seed yield of Hyola401 was more than those of RGS003 (Table 4). There was a negative relationship between seed number and mean air temperature from the beginning of flowering to that of seed filling, explaining 91 and 86% of the variation for Hyola401 and RGS003, respectively (Fig. 3, Table 2). Also there was a positive relationship between seed number and PTQ from the beginning of flowering to that of seed filling (Fig. 4, Table 2), explaining 87 and 83% of the variation for Hyola401 and RGS003, respectively. The slop of this relationship was more in Hyola401 (591946) than RGS003 (492745) (Fig. 4, Table 2), showing the greater response of Hyola401 than RGS003 to PTQ from the beginning of flowering to that of seed filling. Seed number per unit land area was maximized for the cultivars when exposed to the highest PTQ, and to the lowest temperature between the beginning of flowering to that of seed filling. DISCUSSION The mean seed number per unit area in was more than that of (Table 3 and 4). This was probably due to higher incident radiation from Mar. to Apr. in , than that of (Table 1), which was preflowering and seed formation stage of the crop across sowing dates and cultivars. This caused that the seed yield of canola in was more than that of (Table 3 and 4). Environmental conditions (moisture regimes and sowing dates) had major effects on seed number per unit area, and hence seed yield, which ranged from 16 to 378 g m -2, across the five sowing dates and the two years (Table 3 and 4). In both years, seed number per unit area and seed yield were clearly poorest at the latest sowing date (Table 4), probably due to the highest temperatures during flowering period of the crop (Table 5). Seed number was linearly related to aboveground dry matter at the beginning of flowering (Fig. 1), and CGR from the beginning of flowering to that of seed filling (Fig. 2). This is in agreement with what is well established in the literature in some species (Habekotte, 1993; Abbate et al., 1997; Bindraban et al., 1998; Vega et al., 2001). In wheat, Gonzalez et al. (2003) reported that the number of florets per m 2 increased with the increase in main shoot spike dry matter at anthesis, leading to an increased grain number and thereby to a higher grain yield. Bindraban et al. (1998) found a considerable relationship between kernel number per unit area with dry matter, CGR and dry matter accumulation around anthesis. Tayo and Morgan (1979) demonstrated that the number of pods per plant and seeds per pod were regulated by the capability of canola to supply carbon to the inflorescence for the period, from 3 weeks following anthesis. Therefore, as pointed by Spiertz and van Keulen (1980), in this study, the strong relationship of seed number with dry matter parameters around flowering showed that seed number was driven by the availability of carbohydrates at this stage. However, dry matter is the product of growth rate and duration of the growing period, both of which indicate the potential for improvement in seed yield. During flowering and seed set, the relationship between source and sink regulates the availability of assimilates necessary for seed filling (Diepenbrock, 2000). As showed by Fischer (1993) and Bindraban et al. (1998), in this study, environmental conditions such as water supply and sowing date were important factors in determining seed number in canola cultivars. While PTQ integrates the environmental conditions, namely radiation and temperature, it does not consider crop conditions. In this study, PTQ was a good variable in describing the impact of the environmental conditions (radiation and temperature) on seed number, and was a good predictor of seed number per unit area, as showed by Fischer (1985). In both cultivars, seed number was strongly correlated with the mean daily value of the PTQ for pre-seed filling phase. Seed number per unit area was maximized for the cultivars when exposed to the highest PTQ, between the beginning of flowering to that of seed filling. High temperatures, due to delay in sowing date (Table 5), accelerated the rate of plant development, reduced the length of the growing period, and reduced the yield potential (Table 4), as some literature in some species 2170

4 (Entz and Flower, 1991; Chimenti and Hall, 2001). In turn, seed number per plant is the product of the number of pods per plant and the number of seeds per pod. High temperatures during flowering can influence seed number through a reduction in one or more of these components. In fact, the flowering period duration responded to the temperature experienced during that period in the cultivars, increasing its duration with lower temperatures. In this experiment, late sowings led to coincided critical period of flowering with high temperature stress (Table 5), reduced pods per plant, seeds per pod, and seed yield (Table 4). Araus et al. (2002) suggested plant development could be genetically manipulated to lengthen phases associated with seed number determination, even in environments where the seed filling period is subjected to drought stress. In wheat, Slafer et al. (1996) reason that increase in kernel number per unit area could be achieved through extension of early booting to final anthesis period. Chimenti and Hall (2001) proposed there is a critical window for seed number determination in sunflower that begins at floral initiation and finishes 20 days after first anthesis. Seed number exhibit a negative response to temperature during the critical window. However, the mechanism by which temperature influences seed number appears to vary between species. In maize, lower temperatures increase the number of florets per ear (Kiniry and Otegui, 2000), and in wheat lower temperatures improve florets competence in the period leading up to anthesis (Fischer, 1985). In canola, Morrison (1993) showed high temperature could result in lower fertility, because of reduced pollen viability and female fertility, resulting in pollination with no fertilization. Pechan (1988) suggested that barriers may exist between the pollen tube and ovules in canola, and that enzymes are required to dissolve these barriers, facilitating fertilization. High temperatures may have inhibited the production or action of these enzymes, resulting in a reduced number of seeds per pod. CONCLUSION Understanding variation in seed number per unit area, and identifying factors that determine seed number is of major importance in understanding seed yield variation. Increase in canola yield potential can be achieved through increase in seed number per unit area. In this study, a great proportion of the variation in seed number was related to environmental conditions during the critical period of the beginning of flowering to that of seed filling. The ability to match key phenological growth period of the crop to a less stressful growth period in the growing season was an effective means of avoiding the negative impact of temperature and drought stress. Sowing date and supplemental irrigation were very important management tools in minimizing the negative impact of high temperature and drought stresses. The relationship between seed number with dry matter parameters, PTQ and temperature around flowering, over different environmental conditions, showed that these variables were generally applicable to seed number determination. REFERENCES Abbate PE, Andrade FH, Culot JP, Bindraban PS Grain yield in wheat: Effects of radiation during spike growth period. Field Crops Res. 54: Adamsen FJ, Coffelt TA Planting date effects on flowering, seed yield, and oil content of rape and crambe cultivars. Ind. Crops Prod. 21: Andrade FH, Vega CRC, Uhart SA, Cirilo AG, Cantarero M, Valentinuz O Kernel number determination in maize. Crop Sci. 39: Angadi SV, Cutforth HW, Miller PR, McConkey BG, Entz MH, Brandt A, Olkmar KM Response of three Brassica species to high temperature stress during reproductive growth. Can. J. Plant Sci. 80: Angadi SV, McConkey BG, Ulrich D, Cutforth HW, Miller PR, Entz MH, Brandt SA, Volkmar K Developing viable cropping options for the semiarid prairies. Project Rep. Agric. and Agri-Food Can., Swift Current, SK. Araus JL, Slafer GA, Reynolds MP, Royo C Plant breeding and drought in C 3 cereals: what should we breed for? Ann. Bot. 89: Bindraban PS, Sayre KD, Moya ES Identifying factors that determine kernel number in wheat. Field Crops Res. 58: Brandt SA, McGregor DI Canola response to growing season climatic conditions. P In Proc. Workshop on Soils and Crops 97, Saskatoon, SK, Canada Feb Univ. Ext. Press, Saskatoon, SK, Canada. Cantagallo JE, Chimenti CA, Hall AJ Number of seeds per unit area in sunflower correlates well with a photothermal quotient. Crop Sci. 37: Chimenti CA, Hall AJ Grain number responses to temperature during floret differentiation in sunflower. Field Crops Res. 72: Chongo G, McVetty PBE Relationship of physiological characters to yield parameters in oilseed rape (B. napus). Can. J. Plant Sci. 81: 1-6. Diepenbrock W Yield analysis of winter oilseed rape (B. napus L.): a review. Field Crops Res. 67: Egli DB Seed biology and the yield of grain crops. CAB International, Wallingford, UK. Entz MH, Flower DB Agronomic performance of winter versus spring wheat. Agron. J. 83: Fischer RA Number of kernels in wheat crops and the influence of solar radiation and temperature J. Agric. Sci. (Cambridge) 105: Fischer RA Irrigated spring wheat and timing and amount of nitrogen fertilizer. II. Physiology of grain yield response. Field Crops Res. 33:

5 Gan Y, Angadi SV, Cutforth H, Potts D, Angadi VV, McDonald CL Canola and mustard response to short periods of temperature and water stress at different developmental stages. Can. J. Plant Sci. 84: Gonzalez FG, Slafer GA, Miralles DJ Grain and floret number in response to photoperiod during stem elongation in fully and slightly vernalized wheats. Field Crops Res. 81: Habekotte B Quantitative analysis of pod formation, seed set and seed filling in winter oilseed rape (B. napus L.) under field conditions. Field Crops Res. 35: Hall AE Breeding for heat tolerance. Plant Breed. Rev. 10: Harper FR, Berkenkamp B Revised growth-stage key for B. campestris and B. napus. Can. J. plant Sci. 55: Johnston AM, Tanaka DL, Miller PR, Brandt SA, Nielsen DC, Lafond GP, Riveland NR Oilseed crops for semiarid cropping systems in the Northern Great Plains. Agron. J. 94: Kantolic AG, Slafer GA Photoperiod sensitivity after flowering and seed number determination in indeterminate soybean cultivars. Field Crops Res. 72: Kiniry JR, Otegui ME Processes affecting maize grain yield potential in temperate conditions. In: Otegui ME, Slafer GA (eds.), Physiological bases for maize improvement. Food Products Press. The Haworth Press, New York/London/Oxford. pp Kiniry JR, Ritchie JT Shade-sensitive interval of kernel number of maize. Agron. J. 77: Morrison MJ, Stewart DW Heat stress during flowering in summer Brassica. Crop Sci. 42: Morrison MJ Heat stress during reproduction in summer rape. Can. J. Bot. 71: Nielsen DC Water use and yield of canola under dryland conditions in the Central Great Plains. J. Prod. Agric. 10: Ortiz-Monasterio JI, Dhillon SS, Fischer RA Date of sowing effects on grain yield and yield components of irrigated spring wheat cultivars and relationships with radiation and temperature in Ludhiana, India. Field Crops Res. 37: Pechan PM Ovule fertilization and seed number per pod determination in oil seed rape (B. napus) Ann. Bot. (London) 61: Poggio SL, Satorre S, Gonzalo GM Pod and seed numbers as a function of photothermal quotient during the seed set period of field pea (Pisum sativum) crops. Eur. J. Agron. 22: SAS Institute SAS/STAT user's guide, Version 6, 4 th editions, SAS Inst., Inc., Cary, NC. Sinclair TR, Jamieson PD Grain number, wheat yield, and bottling beer: An analysis. Field Crops Res. 98: Slafer GA, Calderini DF, Miralles DJ Yield components and compensation in wheat: opportunities for further increasing yield potential. In: Reynolds MP, Rajaram S, McNab, A (Eds.). Increasing yield potential in wheat: Breaking the barriers. Mexico, D.F.: CIMMYT. pp Spiertz JHJ, van Keulen H Effects of nitrogen and water supply on growth and grain yield of wheat. Proceedings of the Third International Wheat Conference. May 22-June 3, Madrid, Spain. Tayo TO, Morgan DG Factors influencing flower and pod development in oil-seed rape (B. napus). J. Agric. Sci. (Cambridge) 92: Vega CRC, Andrade FH, Sadras VO, Uhart SA, Valentinuz OR Seed number as a function of growth. A comparative study in soybean, sunflower and maize. Crop Sci. 41: Zhang HP, Wang XY, You MZ, Liu CM Water-yield relations and water use efficiency of winter wheat in the North China plain. Irrig. Sci. 19: Table 1. Average monthly temperature and radiation, and rainfall during two years T max ( o c) T min ( o c) Rainfall (mm) Radiation (MJm -2 d -1 ) T max ( o c) T min ( o c) Rainfall (mm) Radiation (MJm -2 d -1 ) Month Oct Nov Dec Jan Feb Mar Apr May June Table 2. Intercept, slope, RMSE and significant level (Pr>F) of linear functions. Relationships a±se b±se RMSE R 2 (%) Pr>F Hyola401 SN and aboveground dry matter at BF ± ± *** SN and CGR, from BF to SF ± ± *** SN and temperature, from BF to SF ± ± *** SN and, PTQ from BF to SF ± ± *** RGS003 SN and aboveground dry matter at BF ± ± *** SN and CGR, from BF to SF -7547± ± *** SN and temperature, from BF to SF ± ± *** SN and PTQ, from BF to SF ± ± *** BF=beginning of flowering; SF= seed filling; PTQ= photothermal quotient. *** Significant at 0.1% level of probability. 2172

6 Table 3. Means of some traits of canola under irrigated and rainfed conditions. Days to flowering Pod number (per plant) Seed number (per pod) Seed yield (g m -2 ) Irrigated 69.7 a 63.5 a 19.3 a 257 a Rainfed 69.4 a 50.3 b 17.1 b 210 b Irrigated 75.9 a 62.9 a 12.6 a 223 a Rainfed 75.0 b 57.0 b 11.2 b 197 b Means followed by the same letter within each group of each column are not significantly different according to the LSD (P=0.05). Table 4. Means of some traits of canola at different sowing dates and cultivars. Days to flowering Pod number (per plant) Seed number (per pod) Seed yield (g m -2 ) Sowing dates 9 Nov a 77.3 a 21.1 a 378 a 6 Dec b 69.8 b 19.2 b 311 b 5 Jan c 57.8 c 18.6 bc 246 c 4 Feb d 44.3 d 18.1 c 172 d 6 Mar e 35.2 e 14.2 d 58 e Cultivars Hyola b 58.0 a 19.2 a 268 a RGS a 55.7 a 17.3 b 198 b Sowing dates 6 Nov a 94.7 a 15.1 a 354 a 6 Dec b 79.0 b 12.2 bc 290 b 5 Jan c 63.0 c 14.0 ab 236 c 4 Feb d 39.1 d 11.4 c 159 d 6 Mar e 24.1 e 6.9 d 16 e Cultivars Hyola b 65.4 a 12.8 a 233 a RGS a 54.6 b 11.0 b 189 b Means followed by the same letter within each group of each column are not significantly different according to the LSD (P=0.05). Table 5. The mean maximum temperature ( 0 C) during flowering period. Hyola401 RGS Sowing dates 9 Nov Dec Jan Feb Mar Sowing dates 6 Nov Dec Jan Feb Mar

7 Figure1. Relationship between seed number and aboveground dry matter at the beginning of flowering in Hyola401 and RGS003. Figure2. Relationship between seed number and crop growth rate (CGR), from the beginning of flowering to that of seed filling in Hyola401 and RGS003. Figure3. Relationship between seed number and mean air temperature, from the beginning of flowering to that of seed filling in Hyola401 and RGS

8 Figure4. Relationship between seed number and photothermal quotient, from the beginning of flowering to that of seed filling in Hyola401 and RGS