Genetic variability analysis of wheat (Triticum aestivum L.) genotypes for yield and related parameters

The present experiment was conducted to find out the genetic variability in 100 different wheat genotypes/germplasms at Agricultural Research Station Baffa, Mansehra, Pakistan. The experiment was laid out in RCBD with three replications. The results of statistical analysis showed significant differences among genotypes for all characters like days to heading, days to maturity, plant height (cm), number of grain/spike, spike length (cm), 1000 grain weight (g), biological yield (tons/ha), grain yield (tons/ha) and harvest index (%). Genetic diversity among genotypes reflect their broad genetic background. The days to heading ranged from 109 to 141 showed by genotypes 3032 and 3008, maturity from 142-184 days by genotypes 3032 and 3023, plant height from 83 to 125 cm by genotypes 3002 and 3077, number of grains/spike from 19 to 75 by genotypes 3173 and 3082, spike length from 8.10 to 12.30 cm by genotypes 3173 and 3082, 1000 grain weight from 21 to 64 gram by genotypes 3148 and 3015, biological yield from 9.30 to 17.50 tons/ha by genotypes 3004 and 3082, grain yield from 1.80 to 5.90 tons/ha by genotypes 3078 and 3082 and harvest index from 14.17 to 44.73 % by genotypes 3144 and 3015. The significant genetic diversity amongst wheat germplasms were recorded in this experiment. Genetic variability analysis revealed that genotypes 3015, 3032 and 3082 were the most promising ones and it is suggested that these lines may be focused and involved in future wheat breeding programme. The use of reported genetic diversity will assist wheat breeders for development of high yielding varieties in future.


Introduction
Wheat (Triticum aestivum L.) is the major cereal crop which is widely cultivated for food purpose in most area of the world including Pakistan.It is popular for high nutritional value and is used in a variety of products.Wheat is considered a good source of protein, carbohydrate, dietary fiber and minerals including calcium, iron, magnesium and phosphorous [1].Wheat is the leading grain crop of the temperate climates and its area and productivity is rapidly increasing throughout the world because of its high adoptability and sustainability under diverse agro ecological zone [2].Major wheat producing countries include China, United States of America, India, Pakistan and Russia.Pakistan is amongst the top ten wheat producing countries where more than 70 % of farming community is directly or indirectly involved in cultivating wheat [3].In Pakistan wheat was grown over an area of 9.1 million hectares which produced 26 million tons [4] while in Khyber Pakhtunkhwa province, the total area under wheat cultivation was 0.72 million hectares [5].There are various yield limiting factors including biotic and abiotic stresses and responsible for low productivity of wheat.Beside harsh environmental conditions, the use of fertilizers, quality of soil and genetic diversity have also great influence on crop yield [6]. Therefore, to withstand under nonconducive and stressful environmental conditions, a broad genetic diversity is required.Due to modern breeding it has been observed that genetic diversity in wheat has been increasingly narrowed which has directly affected the adoptability and sustainability of wheat under disease and unfavourable conditions.Various strategies are used for assessing genetic variability including morphological analysis in field and molecular analysis using molecular markers such as simple sequence repeats (SSR), restriction fragment length polymorphism (RFLP), random amplified polymorphic DNA (RAPD) and diversity arrays technology (DArT) markers [7].Due to unavailability of broad genetic diverse varieties, the average yield of Khyber Pakhtunkhwa province (1807 kg/ha) is much lower than the national average yield (2787 kg/ha) [5].With the increase in population in Pakistan the demands of wheat are continuously increasing.In order to fulfil the demand of population and overcome future food shortage, high yielding and disease resistant varieties of wheat are required.For this purpose wheat varieties with broad genetic background should be developed.1).Two varieties PS. 2015 and NARC-2011 were also included as a checks in the experiment.The genotypes were planted in a well maintained soil condition.The experiment was designed under RCBD (Randomized complete block design) model with three replications.Each plot were consisted of five rows each of 5 m in length with a row to row distance of 30 cm.The crop was grown under normal experimental conditions.The basal dose of fertilizer of 120 Kg N, 60 Kg P2O5 and 40 Kg K2O was applied at sowing.Irrigation was given when required.Normal cultural practices were followed through out the experiment.Data from six randomly selected plants from each replication was recorded.Data was taken on days to heading, days to maturity, plant height (cm), number of grains / spike, spike length (cm), 1000 grain weight (g), biological yield (tons/ha), grain yield (tons/ha) and harvest index (%).The final yield was calculated as mature seed harvested.Grain weight was recorded as weight of 1000 randomly selected seeds taken from each plot.The data was analysed for analysis of variance through M-Stat-C [24] statistical software.Mean comparisons among genotypes were done by further analysis of the significant data through Least Significant Difference (LSD) test at 5% probability level.Grain yield usually depends on other yield related physiological characters of plant.Variation in grain yield are due to genetic diversity of plant materials studied.In the present experiment highly significant variation was recorded for grain yield.The observed genetic variation in grain yield, under the same experimental conditions, represents the high diversity in genetic makeup of wheat genotypes studied.The grain yield ranged from 1.80 to 5.90 tons/ha (Table 2).The line 3082 gave the highest yield (5.90 tons/ha) and was superior amongst all genotypes.Grain yield of two other promising lines 3032 and 3015 was recorded up to 5.60 and 5.10 tons/ha respectively.These lines were statistically at par with high yielding varieties PS. 2015 and NARC-2011 used as checks in the experiment.In contrast, least grain yield was produced by line 3078 (1.80 tons/ha) and 3004 (1.90 tons/ha) which was considered poor genotypes in this experiment.Overall, the genotypes 3082, 3032 and 3015 were the most promising and superior throughout the experiment and therefore, it is suggested that these genotypes may be included in future wheat breeding program.Similar results of grain yield were found by Ishaq

Harvest index (%)
Harvest index was measured in percent by a formula such as grain yield/biological yield x 100.The harvest index ranged from 14.17 to 44.73 % as shown in table 2. Genotype 3015 was observed with highest (44.73 %) harvest index while germplasm 3144 showed minimum (14.17 %) harvest index.
Variation in harvest indices were due to differences in biological and grain yield of tested genotypes.Genotypes with more harvest index and more grain yield were considered superior genotypes.As stated above the genotypes 3082, 3032 and 3015 showed promising results and performed efficiently among all genotypes tested in this experiment.

Conclusion
From the genetic variability analysis of 100 different wheat genotypes, it is concluded that the germplasms 3082, 3032 and 3015 remained superior in term of yield production as well as in other important yield components.It is, therefore suggested that these lines may be brought forward and included in wheat breeding program across the various ecological zones of the country.
Conceived and designed the experiments: M Ghaffar, Performed the experiments: M Ghaffar, Analyzed the data: S Khan & W Khan, Contributed materials/ analysis/ tools: M Ghaffar, Wrote the paper: S Khan, M Ghaffar & W Khan.

Table 2 . Mean performances for various plant trait of wheat genotypes
Grain yield is one of the important and most desirable parameter of crop plant.It is quantitative trait which greatly affected by various genetic and environmental factors.