Ayneband A

Emam Y

Modhej A

Naderi A

Normohamadi G

English

Sydney eScholarship

 1Effects of post-anthesis heat stress and nitrogen levels on grain yield and grain growth of wheat (T. durum and T. aestivum) genotypes  Modhej A1, Naderi A2, Emam Y3, Aynehband A4 and Normohamadi G5 1Dept. of Agriculture, Islamic Azad University, Shoushtar Branch, Iran., 2 Khuzestan Agricultural Research Station, Iran. 3 Shiraz University, Iran 4 Shahid Chamran University, Iran. 5Science & Research Unit, Azad University, Iran   ABSTRACT In order to study the effects of post-anthesis heat stress and nitrogen levels on grain yield and yield components of wheat genotypes, two separate field experiments were conducted in delayed and optimum sowing dates in Ahvaz, Iran in 2006-2007. The Ahvaz site is located in the south west of Iran (32°20' N, 40°20' E) with a subtropical climate. The experimental site had a moderate winter and dry, hot summer. Plants with delayed sowing date experienced heat stress post-anthesis. Each split-polt experiment had a randomized complete block design with three replicates. The N application rates were (50, 100, and 150 KgNha-1) assigned in the main-plots. Sub-plots consisted of six bread and durum wheat genotypes. The results indicated that the grain yield was reduced in the 50 and 100 KgNha-1 compared treatments with 150 KgNha-1 treatments by 41% and 21% respectively under optimum conditions and by 44% and 26% under heat stress conditions. In all genotypes, the grain yield and 1000-grain weight (TGW) reduction under post-anthesis heat stress conditions was 33% and 42%, respectively compared with the non-stressed treatments. The highest and the lowest grain yield reduction due to heat stress were observed in Star (39%) and Vee/Nac (27%) genotypes. The grain yield reduction in low nitrogen and delayed sowing treatments was due reduced grain number and TGW, respectively. In low nitrogen treatments grain number per area was reduced due to a reduction in the number of fertile florets, spikelets-1, spikes. m-2, and spikelets. spike-1. The grain growth period was 23 and 16 days under optimum and post-anthesis heat stress conditions, respectively. Heat stress after anthesis reduced the grain growth rate (12%) and grain growth period (30%) compared with optimum conditions. The indicated results show that agronomic efficiency (ANE) was greater with optimum sowing (2.1 kg per kg) compared with late sowing (1.2 kg per kg). Further research is recommended for a fuller understanding of the effects of heat stress and low N level on yield and yield components of recommended wheat genotypes under stressful conditions such as the south west of Iran.   INTRODUCTION  Wheat is traditionally grown as a cool-season crop, but with the increased availability of more widely adapted semi-dwarf cultivars, wheat production has expanded into warmer regions of countries, where production had previously been restricted to higher altitudes or cooler latitudes (Badrruuddin et al., 1999). Heat, drought and nutrient deficiency are the most important stresses that limit crop production (Entez and Fowler, 1990). Terminal heat stress is a problem in 40% of temperate environments, which cover 36 million ha (Reynolds et al, 2001). Under Mediterranean conditions such as the western part of Iran, heat stress after anthesis is the major grain yield limiting factor in winter sown wheat genotypes. Wheat crops are frequently faced with nitrogen (N) deficiency, due to low rates of N fertilizer application, organic farming practices, or a disjoing between the optimal time for N application, peak crop N demand.. Kernel number (KN), the principal determinant component of grain yield is reduced in crops subjected to pre-anthesis N deficiency (Jeuffroy and Bouchard, 1999).  This study has three main aims: Describing the effects of N deficiency on wheat genotypes with different growth duration, evaluating the effect of post-anthesis heat stress on TGW and grain yield of these genotypes and determining interaction effects of this two important stresses on grain yield of six durum and bread wheat genotypes with different susceptibility to heat and N deficiency stresses.  MATERIALS AND METHODS The experiment was conducted at Ahvaz, south-western of Iran, in the 2006-2007 growing season. The Ahvaz site is located at 20 m above sea level (32°20' N, 40°20' E). Wheat was sown on optimum (22nd Nov) or delayed (20nd Jan) sowing dates. Treatments of each individual experiment (sowing date) were arranged as a split-plot experiment in a randomized complete block design with three replications. Nitrogen rates (50, 100 and 150 kgNha-1) were in main plots and wheat genotypes were in sub-plots. Plants in delayed sowing date experienced heat stress after anthesis. Six genotypes with different growth durations were used. The experiment site had a hot climate with a moderate winter and dry and hot summer. Mean temperature in grain growth period was 22 and 28°C, in optimum and delayed sowings,  2respectively. Total dry matter, relative grain yield and the harvest index (HI) and yield components were estimated after physiological maturity by harvesting interior rows. The harvest area was 1.2 m-2. Grain yield in with heat stress after anthesis was investigated using the stress susceptibility index (SSI) recommended by Fischer and Maurer (1978) and stress tolerance index (STI) recommended by Fernandez (1992). SSI and STI were calculated as equation 1 and 2. PSPiSiYYYYSSI−−=11       Eq. 1             PPiSiYYYSTI 2.=        Eq. 2          where Ysi, Ypi, Ys, Yp and Y2p  were grain yield of each cultivar under stress conditions, grain yield of each cultivar under optimum condition, mean of grain yield in all genotypes in stress and optimum conditions and square of mean grain yield in all genotypes under optimum conditions, respectively. A line of best fit for the linear phase of grain growth was determined as in earlier experiments and the slope of this line was used as an estimate of the grain growth rate (GGR). Effective grain growth duration (EGFD) was estimated by dividing final grain weight to GGR. The agronomic efficiency (ANE) was calculated as bellow:  ANE (kg per kg)= (grain yield at Nx - grain yield at N0) / N applied at Nx   Eq.3  RESULTS  In the late sowing treatment, an increase of 6°C in the average temperature reduced TGW, grain yield (GY), biomass yield (BY) and HI approximately 42%, 33%, 32% and 11% compared to optimum sowing date, respectively. GY reduction was due to TGW decreasing (Table1). The highest and the lowest GY reduction with post-anthesis heat stress condition belonged to Star (long-season) and Vee/Nac (short-season) genotypes respectively. The highest and the lowest SSI were also in these two genotypes, respectively. Results indicated that, the highest and the lowest STI belonged to Showa and Vee/Nac genotypes, respectively. Modhej and Behdarvandi (2006) reported that, genotypes with high GY in optimum and post-anthesis heat stress conditions, had higher STI compared to other genotypes. They also suggested that, the problem with using SSI as a measure of adaptation to stress is that there are cases where SSI has been positively correlated with grain yield reduction in that genotypes whose yield was affected little by the stress also had very low yield potential. This means that the genotypes with low SSI also may have had low stress resistance yield and would not be useful for farmers. Generally, post-anthesis heat stress reduced GY 30%, 35% and 35% in short, middle and long season genotypes, respectively. In late sowing period, heat stress after anthesis reduced GY 32% and 34% in durum and bread wheat genotypes, respectively. BY reduction due to N fertilizer reduction was higher in optimum versus delayed sowing treatments, while the GY had same changes under both conditions, comparatively. Late-sown bread and durum wheat genotypes develop less extensive root systems and may be more vulnerable to drought and heat (Ehdaie and Waines, 2001). Less extensive root system due to delayed sowing may also lead to smaller N absorption and lower agronomic N efficiency. Generally, grain weight reduction with later sowing was due to grain growth duration and rate reduction. Although the grain weight reduction was associated with a shorter duration of grain development, the failure to obtain any compensating increase in the rate of dry matter accumulation, as occurs in the lower temperature ranges, was also considered important. In nitrogen deficiency treatments grain number per unit area is reduced due to reduction in the number of spikes, the number of spikes per spikelet and the number of fertile florets per spikelet.  REFERENCES  1 Badaruddin, M., M. Reynolds., and O. Ageeb. 1999. Wheat management in warm environments: Effect of organic and inorganic fertilizers, irrigation frequency and mulching. Agron. J. 91:975-983. 2 Ehdaie, B., J. G. Waines. 2001. Sowing date and nitrogen rate effects on dry matter and nitrogen partitioning in bread and durum wheat. Field Crop Res. 73: 47-61.  3 Entez, M. H., and B. Fowler. 1990. Differential agronomic response of wheat cultivars to environmental stress. Crop Sci. 30:1119-1123.  4 Fernandez, G. J. 1992. Effective selection criteria for assessing plant stress tolerance. pp. 257-270. In: Proceeding of the International Symposium on Adaptation of vegetables and other food crops In Temperate and water stress. Taiwan.  5 Fischer, R. A, and R. Maurer., 1978. Drought resistance in spring wheat cultivars. I. Grain yield response. Australian Journal of Agricultural Res. 29: 897-912. 6 Jeuffroya, M. H., and C. Bouchard. 1999. Intensity and duration of nitrogen deficiency on wheat grain number. Crop Science 39:1385-1393  7 Modhej, A., and B. Behdarvandi. 2006. Effect of heat stress after anthesis on source limitation of wheat  and barley genotypes. 24th Annual Meeting of ESCB, Belgium. P 28.    3Table.1 Mean spike per m-2, grain per spike (G.S-1), grain growth rate (GGR), effective grain growth duration (EGGD), TGW, GY, BY and HI for N fertilizer treatments and wheat genotypes in optimum and late sowing date.     Ns: Not significant   **: significant at 1% probability level             +: Durum genotypes             MS: Mean square      OS: Optimum Sowing       LS: Late Sowing     Means in each column followed by similar letter (s) are not significantly different at 5% probability level using Duncan's Multiple Range Test.   Treatments Means HI BY (g. m-2) GY (g. m-2) TGW (g) GGR (mg. grain-1 day-1) EGFD (days) G.S-1 Spike.m-2 LS OS LS OS LS OS LS OS LS OS LS OS LS OS LS OS N (kg ha-1)                 150 45a 39b 781a 1303a 354a 512a 27a 45a 1.42a 1.70a 15a 26a 41a 42a 415a 420a 100 39b 40b 667b 1079b 259b 428b 25a 44a 1.48a 1.65a 15a 26a 38a 40a 335b 340b 50 32c 47a 608b 656c 197c 313c 25a 42a 1.50a 1.65a 16a 26a 33b 35b 305b 310b MS 819.26** 445.38** 139948** 1940978** 112864** 180149** 1.18ns 53.68ns 0.21ns 0.09ns 4.22ns 0.66ns 269.24** 269.24** 62367** 62328** Genotypes                 Attila 36bcd 41c 673abc 1059ab 258ab 414ab 21e 36d 1.41d 1.40d 14d 26b 32c 32c 447a 447a Vee/Nac 35cd 36cd 636bc 964ab 235ab 325c 23c 39c 1.85a 2.00a 17b 26b 37b 37b 345b 345b Star 29d 31d 746ab 1180a 219b 364bc 22d 40c 1.66b 1.75b 18a 26b 37b 37b 305b 304b Showa+ 41bc 39cd 760a 1208a 311a 4690a 31a 51a 1.50c 1.71b 17b 28a 35c 35bc 341b 342b D-84-5+ 44ab 58a 677abc 772b 302a 452a 27b 47b 1.50c 1.50c 15c 26b 44a 44a 311b 311b D-83-8+ 49a 54b 618c 893ab 309a 453ab 27b 49a 1.70b 1.59c 13d 28a 38b 38b 353b 353b MS 442.64** 1292.78** 29810** 257109** 320.43** 35645** 177.53** 332.24** 0.44** 0.85** 29.6** 3.6** 12.88** 127.88** 23732** 23709**  4  

Effects of post-anthesis heat stress and nitrogen levels on grain yield and grain growth of wheat ( T. durum and T. aestivum) genotypes

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Effects of post-anthesis heat stress and nitrogen levels on grain yield and grain growth of wheat ( T. durum and T. aestivum) genotypes

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