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Wheat is the largest food crop in the world. It provides more calories in diet than any other crop and is known as "king" of the cereals. The demand of wheat is gradually increasing due to ever increasing population .Grain yield is a complex of many traits and is attributed to its associated components. Therefore, the present studies will be undertaken to estimate the genetic parameters; phenotypic and genotypic variance, coefficient of variability, heritability, genetic advance and correlation. For this, forty eight wheat genotypes will be planted at research area, College of Agriculture Dera Ghazi Khan using Lattice Design with two replications. The data will be recorded on days to heading and maturity, number of productive tillers per plant, plant height, peduncle and spike length, number of spikes per plant, number of spikelets per spike, spike density, number of grains per spike, 100 grain weight and grain yield per plant. Data recorded will be statistically analyzed using Minitab statistical software on a computer program to measure the genetic parameters. The result will be interpreted and information obtained will be helpful for wheat breeders to predict successful wheat breeding program.
IV) NEED FOR THE PROJECT:
Wheat (Triticum aestivum L.) is the most important and widely adopted food cereal of Pakistan. Wheat is leading food grain of Pakistan and staple diet of the people. Wheat quality depends upon endospermic protein, gluten, elasticity viscosity. It is a domesticated and worldwide cultivated crop grown on an area of 9.062 million hectares, producing 23.4 million tons with an average production of 2.6 tons ha-1 (Anonymous, 2009). The stagnant yield of wheat in Pakistan is due to limited diversity in the germplasm and moisture deficit conditions (Noorka et al, 2007). Manifestation of wheat yield fluctuates widely as a result of its interaction with environment because grain yield of wheat is a complex inherited character and is the product of several contributing factors affecting yield directly or indirectly.
The grain yield related traits; plant height, number of tillers, grains number and grain weight are directly associated with yield while peduncle length, spike length, days to heading and days to maturity are indirectly affect the grain yield of wheat.Therefore,the genetic information about these traits are helpful for improving its grain yield.
Different techniques are available to compute the genetic parameters and the index of transmissibility of characters. Knowledge of heritability of traits guides to plant breeder to predict behavior of succeeding generation and helps to know the response for selection. High genetic advance coupled with high heritability estimates offer a most suitable condition for selection. (Larik et al., 1989). However, high heritability and genetic advance clarifies that the selection among genotypes would be effective for yield and its associated components. (Ghandorah & Shawaf, 1993).Similarly the higher the heritability estimates, the simpler are selection procedure (Khan et al., 2008)
Heritability measures the phenotypic variance, which is attributable to genetic cause, has predictive function of breeding crop (Songsri et al., 2008) .The utility of heritability therefore increases when it is used to calculate genetic advance, which indicates the degree of gain in a character obtained under a particular selection pressure. Thus, genetic advance is yet another important selection parameter that aids breeder in a selection program (Shukla et al., 2004). It provides an estimate of genetic parameters to a breeder for selection from a population under certain environment. The present study therefore, will be conducted with following objectives.
To evaluate genetic variability for quantitative traits.
To measure the genetic parameters.
To know the genetic association for grain yield and its components.
To identify the characters of utmost importance used as selection criteria for successful wheat breeding program in future.
V. REVIEW OF LITERATURE
The study of available information in the literature helps researcher to conduct further research. The information regarding correlation and genetic parameters of wheat is reviewed briefly.
Jedynski (2001) explained the correlation and coefficient for grain yield and its components in wheat. He reported heritability estimates which were very high for plant height, 1000- grain weight, intermediate for number of grains per spike and very low for grain yield per plant.
Ashfaq (2002) worked on 45 wheat varieties under drought conditions and found that number of tillers per plant, peduncle length, spike length, number of spikelets per spike, number of grains per spike and 1000-grains weight exercised positive correlation, whereas plant height showed negative correlation with grain yield per plant at both genotypic and phenotypic levels. Plant height showed positive correlation with number of tillers, peduncle length and number of spikelets per spike at both genotypic and phenotypic levels. Number of tillers was positively correlated with all other traits. Peduncle length showed negative correlation only with spikes length. While, spike length was found to be negatively with peduncle length and plant height. Number of spikelets per spike showed positive correlation with all other traits studied. Path analysis revealed direct positive effects of plant height; number of tillers per plant, number of spikelets and number of grains per spike whereas peduncle length, spike length and 1000-grain weight indicated negative direct effects on grain yield per plant.
Khan et al. (2003) studied wheat to determine the broad sense heritability and genetic value for plant height, number of tillers per plant and grain yield per plant. The broad sense heritability values for plant height and number of tillers per plant ranged from 49.83 to 88.83 and 52.25 to 88.82 %, respectively. The broad sense heritability for grain yield per plant ranged from 65.58 to 90.01%.The genetic advance values for plant height, number of tillers per plant and grain yield per plant ranged from 6.30 to 19.88,1.87 to4.42 and 4.95 to 11.61, respectively.
Kashif and Khaliq (2004) estimated moderate to very high broad sense heritability for all the morphological characters except fertile tillers per plant. Plant height exhibited the highest heritability value of 92.08%, while fertile tillers per plant showed minimum value of 40.71%. Genotypically plant height, spike length, spikelets per spike, grains per spike and 1000-grain weight was positively and significantly correlated with grain yield while highly significantly associated phenotypically.
Asif et al. (2004) tested ten bread wheat elite lines and significant variation was observed for all traits studied viz: days to heading, days to maturity, plant height and grain yield. Genotypic and phenotypic correlations, heritability and path coefficient were computed and direct and indirect contributions of each trait towards grain yield were determined. Days to heading and plant height showed relative higher heritability. Grain yield showed significant association with plant height.
Tila et al. (2005) studied correlation and path coefficient analysis in 35 bread wheat varieties. Result showed that days to heading had negative and significant correlation with harvest index and grain yield. Days to maturity were negatively correlated at both genotypic and phenotypic levels with biological yield, harvest index and grain yield and the level of negative genotypic correlation was significant with harvest index and grain yield. Plant height showed negative genotypic and phenotypic correlation with harvest index and grain yield. Positive direct effect of days to heading and days to maturity with grain yield were observed. Path analysis showed the importance in order of harvest index, plant height, days to maturity and days to heading in grain yield.
Hayee (2005) reported that plant height, number of tillers per plant, spike length, peduncle length, number of spikelets per spike and number of grains per spike exhibited positive correlation whereas spike density and 1000-grain weight showed negative association with grain yield per plant in 16 wheat varieties. Spike density was found to be negatively associated with plant height, number of tillers per plant and spike length. Peduncle length showed negative correlation with spike length and 1000-grain weight. 1000-grain weight indicated correlation with plant height and spike density. Path analysis revealed positive direct effect of number of tillers per plant, peduncle length, spike density and number of grains per spike on grain yield per plant. On the other hand, plant height, spikelets per spike and 1000-grain weight exercised negative direct effects on grain yield per plant.
Cheema et al. (2006) reported that a considerable amount of genetic variability present in the research material indicated the possibility of selection for further improvement. Broad sense heritability estimates were observed as 61.62, 72.05, 47.38, 75.58, 79.94 and 80.59%, for number of productive tillers/ plant, spike length, number of spike lets/ spike, number of grains/ spike, 1000-grain weight and grain yield/ plant respectively and genetic advance values at 5% selection intensity were obtained as o.967, 1.230, 1.336, 5.658, 4.110 and 1.826 respectively, for the plant traits studied. It was suggested that selection based on plant traits such as productive tillers/ plant, spike length, grains/ spike and 1000- grain weight could effectively be practiced for developing high grain yielding wheat varieties for the rainfed areas.
Aycicek and Yildirim (2006) reported the estimation of heritability of yield components for 20 bread wheat genotypes. They observed low heritability for the characters such as grain yield, spike number per square meter, plant height, grain number per spike, grain weight per spike, 1000 kernel weight and time to heading.
Memon et al. (2007) evaluated seven F2 progenies and their 8 parental lines of spring wheat for some genetic parameters viz; coefficient of variability, genetic variance, heritability percentage and genetic advance in 7 quantitative characters (grain yield and its associated traits).Highly significant differences were observed viz, plant height, number of grains per spike, seed index and grain yield per plant among all the genotypes; indicating more variability. The highest heritability with more genetic advance for plant in height, number of spikelets per spike and number of grains per spike were observed in progeny Khirman x RWM-9313.Two progenies Soghat-90 showed more number of tillers per plant, spike length and grains per spike with more heritability and genetic gain. The parental line Khirman showed outstanding performance with respect to more number of tillers per plant and grain yield per plant also combining acceptable genetic parameters.
Jamali et al. (2008) conducted an experiment to find out the relation between the yield and yield components with plant height in semi-dwarf wheat. They studied 18 genotypes with 2 check varieties having highest grain yield. Correlations were calculated for pooled yield and yield components data of various genotypes. Plant height showed positive and highly significant correlation with spike length, number of spikelets per spike, number of grains per spike and main spike grain yield but no correlation with number of grains per spikelets. Main spike grain yield exhibited positive and highly significant correlation with plant height.
Akram et al. (2008) revealed positive correlation in case of number of spikelets per spike, number of grains per spike and 1000 grain weight with grain yield at both genotypic and phenotypic levels. However, number of tillers per m2 and spike length contributed negatively towards grain yield at both levels. Plant height was positively correlated with grain yield at genotypic level, whereas negatively correlated at phenotypic levels. It was, therefore, suggested that number of spikelets per spike, number of grains per spike and 1000 grain weight should be given emphasis for future wheat breeding program.
Waqar et al.(2008) evaluated ten wheat genotypes for estimation of heritability and genetic advance of various yield related parameters among all the studied characters, number of grains per spike, 1000 grain weight and grain yield per plant showed high values of heritability coupled with high genetic advance that resulted in proving suitable conditions for selection.
Majumdar et al. (2008) estimated genetic variability and genetic association for grain yield and its components from the study of 20 wheat varieties. Both genotypic and phenotypic variances were highly significant in all the traits with little higher phenotypic variations as usual. Similarly, the low differences between the phenotypic and genotypic coefficients of variations indicated low environmental influences on the expression of these characters. High heritability coupled with high genetic advance was obtained with plant height, grains per spike, 100-grain weight, harvest index and grain yield. Genotypic correlation coefficient was higher than the corresponding phenotypic correlation coefficients in most of the traits. Spikes per plant, grains per spike, spike length, 100-grain weight and harvest index were the most important characters which possessed positive association with grain yield
Ajmal et al. (2009) estimated broad sense heritability, genetic advance and correlation coefficient for various plant characters in six wheat varieties and their twelve F2 progenies. The genotypes were significantly different for plant height, number of tillers per plant, number of spikelets per spike, grain per spike and grain yield per plant. The magnitude of broad sense heritability of plant height, tillers per plant, and grains per spike and grain yield was high with values 0.94, 0.98, 0.92 and 0.91 respectively, and was low in case of number of spikelets per spike. The values of genetic advance ranged from 0.044 in 1000 grain weight to 25.289 in plant height.
Eid.(2009) conducted an experiment of wheat genotypes and found that the mean average for plant height, spike length, number of spikes per plant, number of grains per spike, 50% heading date and 1000-grain weight revealed highly significant differences among genotypes and crosses under both sowing conditions. Low, medium and high heritability was found in different yield traits under study. High heritability accompanied by high genetic advance was observed for spike length and 1000 grain weight. Low heritability coupled with low genetic advance was for plant height and number of grains per spike.
Mohsin et al. (2009) reported from study of 95 synthetic elites of wheat that harvest index exhibited highest heritability value of 83.31% while 1000-grain weight showed minimum value of 42.32%. Grain yield correlated positively with flag leaf area, plant height, biomass, number of spikes, spike length, number of spikelets per spike, number of grains per spike, 1000-grain weight and harvest index.
Khan and Dar (2010) studied 37 wheat genotypes and three checks. They estimated genotypic correlation coefficient were higher than corresponding phenotypic correlation coefficient for all the character combination. Seed yield was significantly and positively associated with number of spikelets per plant, followed by number of effective tillers and 100-seed weight at both phenotypic and genotypic level. Among the significant inter-relationships, the association of days to 75% spike emergence with days to maturity and 100-seed weight were significant and positive but were negative and significantly associated with number of seeds, spikelets per spike and number of grains per spike.
Haq et al. (2010) studied 10 wheat genotypes and found analysis of variance showed highly significant differences among the genotypes for all the traits. The correlation coefficient indicated that spike length, number of spikes per plant, number of spikelerts per spike, number of grains per spike, number of tillers per m2, 1000 grain weight were significantly and positively correlated with grain yield per plant, while days to heading, days to maturity and plant height showed non significant correlation with grain yield per plant.
Lagari et al. (2010) conducted an experiment to estimate heritability in F5 segregating generation of a cross between HT5 (female) and HT37 (male) of bread wheat. The genetic parameters calculated were genetic variance, environmental variance and heritability percentage in broad sense (h2%), genetic advance and heritability coefficient. The highest heritability was observed for spike length (79.3%), number of grains per spike (54.5%) and main spike yield (69.5%) associated with genetic advance (2.8,22.8 and 1.5 respectively).Moderate to high heritability were recorded for peduncle length (48.75%) and number of grains per spikelet (47.2%) which associated with high genetic advance (2.3 and 0.68 respectively).
From the literature reviewed, it is emphasized that genetic parameters estimated from the present research will enable us to make predictions about the possible progress that can be achieved by effective selection. Selection can only be fruitful if desired genetic variability is present in the germplasm.The recommendation will be made for the traits with higher heritability and genetic advance along with positive association with grain yield, would be preferred for selection during breeding program.
VI. MATERIALS AND METHODS
The present project of genetic investigation will be carried out at College of Agriculture D. G. Khan. Forty eight genotypes will be sown in field during crop season 2009-10 using Lattice Design with two replications. Keeping plot size of 0.6 m2, plant to plant and row to row distance will be maintained as 10 cm and 30 cm respectively. All recommended management practices will be applied equally to all genotypes. The data will be recorded from 10 randomly selected plants from each plot for the following traits and average will be computed.
Days to heading.
Days to maturity.
Number of productive tillers per plant.
Plant height (cm).
Peduncle length (cm).
Spike length (cm).
Number of spikes per plant.
Number of spikelets per spike.
Number of grains per spike.
100 grain weight (g).
Grain yield per plant.
The data will be statistically analyzed using the method as advocated by Steel et al, 1997. Genetic parameters (genotypic and phenotypic variance, heritability, genetic advance and correlation) will be calculated following different methods as mentioned by Singh and Narayanan (2000).Results will be interpreted for the genetic information to be utilized in future breeding programs.
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