Evaluation of some wheat genotypes growing under heat stress condition in two environments in Bangladesh

The study was carried out from November to March, 2013-2014 in two agricultural research centers/stations: Wheat Research Centre (WRC; 23° 11' 14.52" N, 89° 11' 11.99" E; 10.4 meter above sea level, masl), Nashipur, Dinajpur and Regional Agricultural Research Station (RARS), Jashore (23° 11' 14.52" N, 89° 11' 11.99" E; 10.4 masl) of the Bangladesh Agricultural Research Institute (BARI). Sixteen genotypes along with two check varieties BARI Gom 21 and BARI Gom 26 were evaluated in Randomized Complete Block Design (RCBD) with three replications under irrigated timely sown (ITS) and irrigated late sown heat stress (ILS) conditions to find out the heat-tolerant wheat lines for future breeding program to develop heat-tolerant wheat varieties. Significant variations were observed among tested genotypes on phenology, yield and yield contributing characters at late sown heat stress condition (ILS) in both locations. The higher yield across location and genotype was recorded in ITS condition (4224 kg ha-1) than ILS condition (3113 kg ha-1). Regarding environmental locations, Dinajpur was better placed for wheat production. Among the tested genotypes, Gen-3, gen-8, Gen-10, Gen-11, and Gen-16 showed better performance under ILS condition and these genotypes were selected for the future breeding programs to develop heat-tolerant varieties. The selected genotypes had high yield, bold and plump grains with better tolerance to Bipolaris leaf blight (BpLB) and resistance to leaf rust diseases.


Introduction
Wheat is the staple food of one-third population of the world and is one of the major foods for Asia.It is originated in southwestern Asia and a major agricultural commodity since prehistoric times.Among the cereals, it is the most widely cultivated one.Wheat is grown in all temperate countries and most of the sub-tropical countries as well as at high elevations of some tropical countries.
Wheat is nutritious, concentrated readily stored and transported and easily processed to give highly refined raw foods.It is used as human food to achieve calorie and protein.Wheat grains contain 17 percent calorie and 19 percent protein [1].The consumption of wheat per capita has increased from 17.4 kg in 1972 to 60 kg in 2007 [2] in developing countries.
It is the second most important grain crop after rice and also playing an important role in attaining food security in Bangladesh but its yield is lower compared to other wheat-growing countries in the world [3].Till now the maximum yield of existing wheat varieties in the research field is 4.0-5.0t ha -1 [4,5], but in farmers' fields, it is < 3 t h a -1 [6] due to several stresses.
Heat stress is one of the major constraints for wheat cultivation in Bangladesh.Late planting receives heat stress in Bangladesh and effects on the growth of wheat resulting in yield loss of wheat compared to optimum sowing.Each day delay in sowing of wheat after 30 th November onward decreases grain yield at the rate of 36 kg ha -1 day -1 [7].A huge amount of land in Bangladesh where wheat is followed by the transplanted Aman rice or where soil remains wet due to excessive rainfall, seeding is continued up to January and wheat crop falls in heat stress condition resulting in lower yield [8,9,10].Therefore, genotypes having heat resistance traits are most desirable for wheat cultivation in this region.In this regard, this trial was conducted to identify heat-tolerant wheat varieties for the future breeding programs.

Designs and experimental procedures
Sixteen promising wheat genotypes along with two checks (BARI Gom 21 and BARI Gom 26) were evaluated in this study to identify suitable genotypes for growing in Bangladesh condition.The experiment was laid out in a randomized complete block design (RCBD) with three replications.The genotypes were evaluated under irrigated timely sown (ITS) and irrigated late sown (ILS) conditions at both locations.In a timely sown condition, all genotypes were sown in lines by hand on November 22 at Dinajpur and November 20 at Jashore whereas in late sown heat stress condition all the genotypes were sown on December 21 at Dinajpur and December 20 at Jashore.The seeding rate was 120 kg per hectare for each genotype.Before sowing, seeds of all varieties were treated with a popular fungicide, Provax-200 WP, which contains carboxin and Thiram (marketed by Hossain Enterprise Bangladesh Ltd., in association with Chemtura Corp., USA).Furadan 5G (containing carbofuran, marketed by FMC International S.A. Bangladesh Ltd.) was broadcasted at 15 kg per hectare for controlling soil-borne insects.Seeds were sown continuously in 5 m long 6 rows plot with a row spacing of 20 cm.

Intercultural operations
WRC recommended fertilizers which are N, P, K, S, and B, respectively, at 100, 27, 40, 20, 1 kg ha -1 were applied.During final land preparation, two-thirds of N and a full amount of the other fertilizers were applied as basal.The remaining N fertilizer was applied immediately after the first irrigation (18 days after sowing, DAS) while second, third and fourth irrigations were applied at 50, 75 and 85 DAS.Mulching was done at 25 DAS and hand weeding at 45 DAS.Phenology data like days to heading and maturity were recorded during the crop growth stage.The crop was harvested at full maturity on 30 March in 2014.Grain yield (GY) and yield contributing characters were measured from the middle 4 rows (4 m 2 area) among 6 rows.The harvested samples from each plot were bundled separately, tagged and manually threshed on a threshing floor after drying the bundles thoroughly in bright sunshine.GY and 1000-grain weight (TGW) were measured at 12% moisture in grain [12].

Statistical analysis
Statistical analysis was conducted by the CropStat program with an F-test at 1% and 5% levels.

Days to heading
It is the developmental stage in which the spike partially appears to emerge from its enclosing sheath is also called heading [13].The time taken for the heading is entirely dependent on growth conditions as well as the genetic makeup of specific genotypes [5,8,9].Days to heading of different genotypes were significantly varied by genotypes, locations and sowing times (Table 1, 2, 3, 4).It was earlier at the optimum sowing condition.In case of environmental condition, maximum genotypes took a long time to head both sowing conditions under the weather conditions of Dinajpur than Jashore.Maximum genotypes showed faster heading at late sowing conditions than optimum sowing conditions under the weather condition of Jashore.This result was similar to the result of Hossain et al. [14] where they found days to heading was faster in late sowing conditions than timely sowing conditions in some spring wheat genotypes.Among the genotypes, Gen.-4, Gen.-5, Gen.-6, and Gen.-10 took less time as compared to check variety BARI Gom 21 and BARI Gom 26.These differences of days to heading under ITS and ILS conditions in both locations might be due to environmental instability especially temperature.This result was confirmed by several studies [15,16,17,18] where they found that the crops complete their life cycle much faster in high temperatures than normal temperature conditions.However, the variation of phenological stages depends on genotypes [19].

Days to maturity
In the present study, similarly, days to heading days to maturity of wheat was also significantly influenced by sowing time, environmental locations and genotypes (Table 1, 2, 3, 4).In both locations, late sown wheat genotypes completed their life cycle very quickly than timely sown while all genotypes took a long time to complete their life cycle under the weather condition of Dinajpur than Jashore condition might be due the environmental factors especially temperature.Among the genotypes, Gen.-4, Gen.-5, Gen.-10, Gen.-14, Gen.-16, and Gen.-18 took a short time for maturity than both check varieties might be due to the different genetic makeup.This result was similar to the result of Hossain et al. [14] where they reported that late sown wheat completed their life cycle faster than timely sown wheat.Several reports showed that days to maturity of wheat genotypes affected by environmental factors especially temperature and their inherent characters [20,21,22].

Spike per square meter
Among the parameters of yield contributing characters, spikes/effective tillers are one of the important parameters.The maximum number of spikes per m -2 was at ITS condition in both locations (Table 1, 2, 3, 5).In the present study, in the case of locations, the favorable environment for spike m -2 was Dinajpur compared to Jashore both in ITS and ILS conditions.Tahir et al. [23] also confirmed our result who noticed that the total number of tillers per m 2 was significantly higher on 20th November than the 20th December.The tillering capacity of the late sowing crop was lower due to less soil moisture (drought), high soil and air temperature and low relative humidity (RH).The highest tiller production on 15 November sowing was due to elongate vegetative phase weather during this period as reported.Considering the genotypes, highest spikes m -2 was recorded in genotype 'Gen.-3,followed by 'Gen.-18,'Gen.-12,Gen.-15, and Gen-10 and the minimum were produced by Gen-7 and Gen.-16.Genotypespecific spikes m -2 was due to the genetic makeup of a genotype as well as location-specific environmental factors.

Grains per spike
Performance of the genotypes for the trait grains per spike under different sowing time and locations was presented in Tables 1, 2, 3, 5.The wheat reproductive stage is the most sensitive period to temperature [14].In high-temperature stress (above 30 °C) at the flowering stage, nearly all field crops reducing grain set ultimately decreased the grain number per spike due to lower fertilization caused by pollen sterility and/or ovule abortion that ultimately decreases the grain number per spike [24,16].In the present study, the highest grains spike -1 was recorded in ITS condition (Table 2), due to friendly weather condition, that finally helps to increase grain set.In the case of environmental condition, the environmental condition of Dinajpur was better for setting grains per spike than Jashore (Table 3).Among the genotypes tested in this study, Gen-8 and Gen-9 produced higher grains per spike compared to both checks.The genotypic difference might be due to the genetic variation, climatic and edaphic factors as determine among the field conditions.

Thousand-grain weight
Heat stress under late sown condition reduces TGW due to a decrease in individual grain weight, while in optimum sowing.Top TGW is gotten due to the maximum individual grain weight that might be due to favorable environmental conditions.In our present study, wheat is sown in ITS condition (20th November) produced the maximum TGW and the minimum TGW was achieved from ILS condition (30th December sowing) (Table 1, 2, 3, 6).Considering on locations, highest TGW was achieved in Dinajpur due to favorable weather condition during the growth stage of wheat (Table 6).In the case of genotypes, the highest TGW was observed in Gen.-16, followed by Gen.-7, 13 and check BARI Gom 26, and the minimum TGW was in 'Gen.-9'.Location-specific sowing dates showed that all genotypes achieved the highest TGW under ITS condition.While in ILS condition, 'Gen.14 achieved the top TGW in Dinajpur and 'Gen.-13'gave the highest TGW in Jashore location.Reduced in grain weight in two locations might be due to late sowing that decreased in the growth stage and curl of grain, due to high-temperature dominate during in milk and grain filling stage.High temperature (soil, air) and a shortage of soil moisture (drought) in late sowing reduced individual grain weight, which finally affected 1000-grain weight, due to early heading and abnormal maturity.

Table 1 .
Effect of sowing times on yield and yield contributing characters of wheat genotypes, 2013-2014

Table 2 .
Effect of locations on yield and yield attributes of wheat genotypes, 2013-2014

Table 3 .
Yield and yield attributes of wheat genotypes varied due to their inherent characters, 2013-2014

Table 4 .
Effects of genotypes, locations and sowing times on heading and maturity days, 2013-2014

Table 5 .
Effects of locations, sowing times and genotypes on spike per square meter and grains per spike, 2013-2014

Table 6 .
Effect of genotypes, sowing times and locations on TGW and grain yield, 2013-2014