The study of dry matter and nitrogen remobilization in different rice cultivars under water stress conditions

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1 Proceedings of The Fourth International Iran & Russia Conference 957 The study of dry matter and nitrogen remobilization in different rice cultivars under water stress conditions Hemmatollah Pirdashti 1, Zinolabedin Tahmasebi Sarvestani 1, Ghorbanali Nematzadeh 2 and Abdelbaghi Ismail 3 1- Ph.D. Student of Agronomy and Assistance of Professor. Department of Agronomy, College of Agriculture, Tarbiat Modarres University, Tehran, Iran. P.O.Box: Tel: 011(9821) Fax: 011(9821) Pirdasht@yahoo.com 2- Associated Professor, Department of Agronomy and Plant Breeding, College of Agriculture, University of Mazandaran, Sari, Iran.3- Plant Physiologist, Crop, Soil and Water Siences Division, International Rice Research Institute(IRRI), DAPO 7777, Metro Manila, Philippines Abstract: In order to study dry matter and nitrogen remobilization in different rice cultivars under water stress conditions, an experiment was conducted at Rice Research Institute of Iran Deputy of Mazandaran (Amol) during A split factorial experiment based on complete randomized block design with three replication were conducted. Main plots included drought stress on four levels (continuous irrigation or no water stress as a control, drought stress in vegetation, flowering and grain filling phases) and cultivars in four level (Tarom, Khazar, Fajr and Nemat) with nitrogen fertilizer in two levels (92 kg N. ha -1 and 115 kg N. ha -1 ) were arranged factorialy in sub plots. Results showed that dry matter remobilization portion in grain yield ranged from 9.2 to 28.6 percent in different genotypes. Different genotypes had different nitrogen remobilization, so that in terms of stem and other leaves nitrogen remobilization Tarom cultivar, in terms of flag leaf remobilization, Nemat cultivar and in terms of shoot nitrogen remobilization Tarom cultivar had relative advantage to other genotypes. There were significant differences among different drought stress treatments in terms of dry matter remobilization portion in grain yield, so that the highest amount were related to drought stress in flowering phases. There was a positive and significant correlation among grain yield and stem, other leaves, flag leaf and total shoot dry matter and nitrogen remobilization. Key words: Rice, Water stress, Yield, Remobilization and Nitrogen. Introduction Rice (Oryza sativa L.) is the primary food grain consumed by almost half of the world s population (Dowling et al., 1998). Rice culture is known for its crucial dependence on an adequate supply of water. Besides supplying water to meet the plant s evapotranspiration demand, the ponded water layer also helps suppress weed growth and increase the availability of many nutrients (De Datta, 1981). Unlike other food crops, rice suffers from water stress even at soil water contents that exceed field capacity (Bhuiyan et al., 1998). The drought injury of a rice plant noticeably varies according to its growth stages when it undergoes drought (Tsuboi, 1995; Jongdee et al., 2002). In other hands, two physiological process are involved in grain growth: utilization of photosynthates through current photosynthesis, and remobilization and translocation of substance accumulated before anthesis (Akita, 1989). Cock and Yoshida (1971) and Marsehner (1993) reported that about 20 % to 40 % of the grain carbohydrate are from previously stored carbohydrate. On the other hand, stem carbohydrate reserves have been estimated to contribute about 18% of the final grain yield in rice under normal condition (Venkateswarlu, 1976). During ripening, however, nitrogen accumulates in the spikelet of the ear mainly as protein and the

2 Proceedings of The Fourth International Iran & Russia Conference 958 protein content at harvest accounts for 8-10 % of the final dry matter content (Iwasaki et al., 1991). Tahmasebi Sarvestani et al (1995) reported that in wheat plants among different parts of the shoot the remobilization of dry matter was greater from the internode than other parts of the shoot and there were comparatively small amount of these compounds remobilize from the leaves. On the other hand, leaves were the most important parts of the shoot in terms of the remobilization of nitrogen. During the grain filling period, N is gradually translocated from the vegetative plant parts to the developing rice panicles. Remobilization and transfer of the pre-stored food in vegetative tissues to the grains in monocarpic plants require the initiation of whole plant senescence. However, mechanisms by which plant senescence promotes remobilization of assimilates are rather obscure. The present experiment was conducted to investigate the remobilization of dry matter and nitrogen from the vegetative parts of different rice genotypes during grain filling under water stress at different growth stages. Materials and Methods A field experiment was carried out in Rice Research Institute of Iran Deputy of Mazandaran (Amol) located in north of Iran (52 22 N, E, altitude 28 m) during This experiment was laid out to evaluate varietal performance of four rice cultivars in terms of dry matter and nitrogen remobilization as affected by water stress. The experiment was laid out in split-factorial with main-plot treatments in a randomized complete block design and three replications. Main-plots were four water stress regimes (water stress in vegetative stage, water stress in flowering stage, water stress in grain filling stage and control or no water stress). Control was irrigated as required to ensure a high level of standing water throughout crop growth. Plants in water stress treatments were grown under favorable water conditions with supplementary surface irrigation throughout the crop cycle while irrigation was interrupted to induce drought stress at around vegetative, flowering and grain filling stages. Drought is defined here as any situation where there is no standing water and the water content in the rooted soil is below saturation. The vegetative stage of growth is defined as the period from transplanting to panicle initiation and the reproductive stage from panicle initiation to flowering (flowering stage) and from the end of flowering stage to harvest (grain filling stage). Sub-plots were four contrasting cultivars. A mixed commercial fertilizer was applied at the rate of 92 kg N ha 1,100 kg P 2 O 5 ha -1, and 100 kg K 2 O ha -1. Basal fertilizer of nitrogen was applied around the time of transplanting and top dressing of N was applied around tillering and panicle initiation in July. There was a significant buffer area between the trials (replication, main and sub plots) to ensure no lateral water and nitrogen movement from on plot to others. Plot size was 3 * 6 m. Seedling between days old used for transplanting and three seedlings were transplanted to each hill, spaced at 25*25 cm. Weeds were controlled manually, and insects and diseases controlled by applying insecticides and fungicides respectively. Maximum and minimum air temperature, rain fall and class a pan evaporation were recorded daily at 08:00 h. the measurment made by the closest meteorological station to the experiment station. For tiller number determination plants were sampled from a 1*1 m area in each plot on the last day of water stress. The last sampling took place at maturity. At the flowering and the maturity, plants were collected and separated different parts (stem, flag leaf and other leaves) were dried under 75 C during 72 hours and then weighed. The total nitrogen content of each sample was determined by the Kjeldahl- digestion method. Amount of dry matter and nitrogen remobilisation accounted as followed: Amount of dry matter or nitrogen

3 Proceedings of The Fourth International Iran & Russia Conference 959 remobilisation (mg per plant)= amount of dry matter or nitrogen at flowering minus amount of dry matter or nitrogen at maturity except grain. Analysis of variance based on the split-factorial was carried out for all characters. The 2-year data underwent a repeated-measures data analysis by using a combined analysis of variance across years All statistical tests were carried out using the Statistical Analysis System (SAS Institute 1996). Results and Discussion Results showed that water stress had a significant (P<0.01) effect on stem, flag leaf, other leaves and shoot dry matter and nitrogen remobilization in both year (Table 1 and 2). Water stress at different growth stages reduced the amount of dry matter and nitrogen remobilization components. Among different water stress treatments imposing water stress at flowering stage had the lowest amount of dry matter and nitrogen remobilization than other treatment (table 1 and 2). Davidson and Chevalier (1992) reported that water stress reduced both storage and translocation of watersoluble carbohydrates. There were significant differences among different drought stress treatments in terms of dry matter remobilization portion in grain yield (9.2 to 29.7 %), so that the highest amount were related to drought stress in flowering phases (Table 1). Chaturvedi and Ram (1996) found that rice stored a high amount of carbohydrates in stem and these carbohydrates have an important role in water stress conditions. Dry matter and nitrogen remobilization portion in grain yield ranged from 20.5 to 28.6 percent and to percent in different genotypes, respectively (Table 1 and 2). Different genotypes had different nitrogen remobilization, so that in terms of stem and other leaves nitrogen remobilization Tarom cultivar, in terms of flag leaf remobilization, Nemat cultivar and in terms of shoot nitrogen remobilization Tarom cultivar had relative advantage to other genotypes. There was a positive and significant correlation among grain yield and stem dry matter (r=0.71**) and nitrogen (r=0.44**) remobilization, other leaves dry matter (r=0.38**) and nitrogen (0.48**) remobilization, flag leaf dry matter (r=0.53**) and nitrogen (r=0.51**) remobilization and total shoot dry matter (r=0.78**) and nitrogen (0.52**) remobilization. Conclusion Result of the present study indicate that there is a difference in dry matter and nitrogen remobilization in different varieties and water stress treatments under Amol weather conditions. Differential responses to the treatment and also in different parts of the shoot suggest that the remobilization of dry matter and nitrogen be controlled through different mechanisms and have a important role in grain yield especially in drought conditions. This result can help physiologists and breeders to determine physiological and morphological features of varieties that contribute most to increasing yield production. Acknoledgment Financial support by the Tarbiat Modarres University and Rice Research Institute of Iran Deputy of Mazandaran (Amol) highly appreciated.the assistance of Mr. Heshmatollah Pirdashti and Mr. Majid Rahimi on data collection is gratefully acknowledged. References Akita, S (1989) Genotypic Variation in Mineral Uptake of Rice Mutant and Parent.3 th Ed. (Los Banos, Philippines).

4 Proceedings of The Fourth International Iran & Russia Conference 960 Bhuiyan, SI, Tuong, TP and wade, LJ (1998) Management of water as a scarce resource: issues and options in rice culture. In: Sustainability of Rice in the Global Food System. eds. Dowling, NG, Greenfield, SM and fisher, KS. Pp International Rice Research Institute. Manila, Philippines. Cock, JH and Yoshida, S (1971) Accumulation of C 14 labeled carbohydrate before flowering and its subsequent redistribution and respiration in the rice plant. Proceeding of Crop Science Society of Japaneses, 41: Davidson, DY and Chevalier, PM (1992) Storage and remobilization of water- soluble carbohydrate in spring wheat stems. Crop Science, 32: De Datta, SK. (1981). Principles and Practices of Rice Production. John Wiley and Sons, New York, USA, 618 p. Dowling, NG, Greenfield, SM and fisher, KS (1998) Sustainability of Rice in the Global Food System. International Rice Research Institute. Manila, Philippines, 404 pages. Iwasaki, Y., Mae, T., Makino, A., Koji, O. and Ojima, K (1992) Nitrogen accumulation in the inferior spikelet of rice ear during ripening. Soil. Science and Plant Nutrition, 38: Marsehner, H (1993). Mineral Nutrition of Higher Plants. 2 nd Ed. Stuttgart, Germany. Thamasebi Sarvestani, Z (1995) Water stress and remobilization of dry matter a nd nitrogen in wheat and barley genotypes. Ph. D. Thesis, University of Adelaid, Australia, 240 p. Jongdee, S., mitchell, JH and Fukai, S (1997) Modeling approach for estimation of rice yield reduction due to drought in Thailand. In: Breeding Strategis for Rainfed Lowland Rice. eds. Fukai, S., Cooper, M. and Salisbury, L. Proceedings of an International Workshop, Ubon Ratchathani, Thailand, 5-8 November ACIAR Proceedings No. 77, pp Tsuboi, Y (1995) Wind damage and drought damage. In: Sceince of the Rice Plant. eds. Matsuo, T. and Hoshikawa, K. pp Vol.2. Food and Agriculture Policy Research Center, Tokyo, Japan. Venkateswarlo, B Source- sink interrelationships in lowland rice. Plant and Soil, 44:

5 Proceedings of The Fourth International Iran & Russia Conference 961 Table 1. Dry matter remobilization from different parts of the shoot in different genotypes under different water stress and nitrogen conditions. Source of Variation Dry matter remobilization Stem Other leaves Flag leaf Total Remobilization portion in grain yield Water Kg.ha -1 % stress** W a a 192.1a 196.6a 73.8a 76.3a a a 9.2bc 22.7b W b 906.1b 139.6c 142.9c 51.2c 53.9c b b 22.5c 22.3b W c 751.8c 116.5d 121.3d 30.8d 33.1d 893.5c 906.3c 29.7a 28.4a W b 623.3b 172.5b 176.1b 59.2b 61.6b b b 23.6b 22.6b Cultivar Tarom 632.5c 641.0c 201.8a 205.0a 4.8d 7.4d 839.1d 853.4d 21.9c 20.5d Khazar 956.9b 967.9b 132.3c 137.9c 39.7c 41.8c c c 26.6b 25.8b Fajr 115.8a a 102.9d 108.3d 123.2a 125.9a a a 28.6a 27.6a Nemat 953.3b 641.0c 182.8b 185.8b 47.2b 7.4d b b 21.7c 22.0b Nitrogen N b 873.4b 144.9b 148.9b 44.0b 46.6b b b 23.4b 22.9b N a 996.3a 165.4a 169.6a 63.5a 65.9a a a 25.9a 25.2a CV Two Year 925.3a 934.8a 155.2a 159.3a 53.8a 56.3a b a 24.0a 24.7a Mean*** *Means followed by the same letters in each column are not significantly different (at 5% level) according to duncan's multiple ranges test. ** W0 = control or continuos irrigation ; W1= drought stress at vegetative stage; W2= drought stress at flowering stage; W3= drought stress at grain filling stage; N1= 92 kg N per hectare; N2= 115 kg N per hectare. *** Means followed by the same letter in each row (a pair numbers) are not significantly different (at 5% level) according to duncan's multiple ranges test. Table 2. Nitrogen remobilization from different parts of the shoot in different genotypes under different water stress and nitrogen conditions.

6 Proceedings of The Fourth International Iran & Russia Conference 962 Source of Variation Nitrogen remobilization Stem Other leaves Flag leaf Total Remobilization portion in grain Nitrogen Water Kg.ha -1 % stress** W b 10.29a 8.87b 8.83a 3.50b 4.79ab 22.95b 23.91a 64.67b 66.00b W1 8.58c 8.50b 7.45c 7.25b 3.58b 4.37b 19.62c 20.12b 52.19c 52.34c W2 5.75d 5.92c 4.75d 4.79c 2.71c 3.04c 13.21d 13.75c 41.71d 42.34d W a 10.83a 9.62a 9.20a 4.17a 5.29a 24.92a 25.33a 73.72a 71.92a Cultivar Tarom 11.25a 10.83a 9.54a 8.91a 2.70c 4.50a 23.50a 24.25a 57.08b 57.93b Khazar 7.71c 7.62d 6.58c 6.42d 3.41b 4.12b 17.71c 18.16c 49.13c 49.02c Fajr 8.12c 8.25c 7.04c 7.08c 3.71ab 4.08b 18.87c 19.42c 64.97a 63.75a Nemat 8.95b 8.83b 7.54b 7.67b 4.12a 4.79a 20.62b 21.29b 61.13ab 61.91ab Nitrogen N1 8.41b 8.27b 7.15b 6.97b 3.23b 4.08b 18.79b 19.23b 55.75b 55.06b N2 9.60a 9.50a 8.21a 7.06a 3.75a 4.66a 21.56a 22.22a 60.41a 60.67a CV Two Year 9.01a 8.88a 7.67a 7.52a 3.49b 4.37a 20.17a 20.78a 58.07a 58.15a Mean*** *Means followed by the same letters in each column are not significantly different (at 5% level) according to duncan's multiple ranges test. ** W0 = control or continuos irrigation ; W1= drought stress at vegetative stage; W2= drought stress at flowering stage; W3= drought stress at grain filling stage; N1= 92 kg N per hectare; N2= 115 kg N per hectare. *** Means followed by the same letter in each row (a pair numbers) are not significantly different (at 5% level) according to duncan's multiple ranges test.