Genetic variability and correlation studies for morphological and yield traits in maize ( Zea mays L . )

This experiment was conducted at the University of Agriculture Peshawar, during spring 2015 to estimate genetic variability in maize genotypes for morphological and yield related traits. The study was laid out in randomized complete block design with three replications using 22 genotypes comprising 20 hybrids and two local checks. Data were taken on days to tasseling, anthesis, silking, anthesis-silking interval, plant height, ear height, flag leaf area, cob length, kernel rows cob, 100-kernel weight and grain yield. Significant (P≤0.01) variability among the hybrids was found for all the traits. Mean values for the traits ranged between 49-65(tasseling), 52-70 (anthesis), 52-72 (silking), 0-4 (anthesis silking interval), 161.7-213.5(plant height), 53.898.6(ear height), 422.4-662.5(flag leaf area), 17.2-24.5(cob length), 13.0-17.0(kernel rows cob), 25.3-38.3(100-kernel weight) and 2770-7500(grain yield). Hybrid-1 performed better for yield and yield associated traits under the tested agro-climatic conditions. Grain yield had significant and positive correlation with ear length (r=0.45) and non-significant but positive correlation with plant height (r=0.23), ear height (r=0.41), flag leaf area (r=0.03) kernel rows per cob (r=0.05) and 100 kernel weight (r=0.21). The positive correlations suggested that the desired characters in these hybrids could be improved simultaneously in further maize breeding programs. Based on the result of current studies hybrid could be recommended for commercial cultivation of maize hybrids for the agro-climatic condition of Peshawar.


Introduction
Maize (Zea mays L.) is the third most important cereal crop after wheat and rice worldwide.Its grain is highly nutritive, with 4-4.5% fats, 70-72% carbohydrates, oils 2-2.8% and 9.5-11% proteins [1].According to Food and Agriculture Organization (FAO) worldwide maize was cultivated over the area of 118 million hectares with an annual production of 600 million metric tons.In Pakistan, maize is the fourth major crop after wheat, cotton, and rice.The area under maize cultivation in Pakistan was 1168.5 thousand hectares with a production of 4944.2 thousand tons [2].Genetic variability for different traits among the maize genotypes is a key factor for crop improvement [3].High yielding and stable cultivar is the major goal of almost all breeding programs.Uniform performance of genotypes both with low and high yield across different maize environment is desirable and referred as yield stability [4].The grain yield is a quantative (polygenic) trait in nature, controlled by many genes and also interacts with environmental conditions thus have low heritability [5].During the evaluation of maize genotypes for grain yield comparison several agronomic traits are taken into consideration.Among these, anthesis silking interval, plant height, ear height, kernel rows per cob, cob length and cob diameter are significantly important [6].In most of the maize breeding programs genotypes are selected on the basis of desirable combination of traits and not only its yield potential.
Hence, yield improvement can be achieved easily through direct selection as well as indirect selection through yield component because of complex nature of a trait [7].Evaluation of genotypes for traits is an important step towards the development of varieties or hybrids.Breeders usually evaluate advanced breeding material to select superior genotypes for generation advancement or possible release as new variety.Hence it is important to explore relationships among morphological and yield associated characters in maize hybrids [8].This experiment was therefore conducted to investigate the magnitude of genetic variability and trait association of various plant traits with grain yield in maize hybrids.

Materials and methods
During spring crop season 2015, a set of twenty maize hybrids (Table 1) along with two local checks were evaluated for morphological and yield related traits in Randomized Complete Block (RCB) design using three replications at The University of Agriculture, Peshawar.Each plot consisted of two rows.The row length was 5 m with 0.75 m spacing between them.Fifty seeds were planted in each plot on 27 th , March 2015.Normal culture practices including tillage, hoeing, irrigation, application of fertilizer etc. were performed during whole cropping season.Data recorded included days to tasseling, anthesis and silking, anthesis-silking interval (ASI), plant height, ear height, flag leaf area, ear length, kernel rows cob -1 , 100 kernel weight and grain yield.Data on flowering traits and grain yield were recorded on plot basis while for yield and yield components, the data were taken on a sample of ten plants.Data recorded were subjected to analysis of variance (ANOVA) and correlation coefficients were calculated using computer software SPSS v. 16 who also stated a positive relationship between anthesis silking interval and grain yield.Synchronization between anthesis and silking leads to higher seed setting and ultimately higher grain yield.

Plant height
Mean square values exhibited highly significant differences among the maize hybrids for plant height (

Kernel rows cob -1
Significant (P≤0.01)variations were found for kernel rows cob -1 among the maize hybrids (Table 2).Mean values for kernel rows cob -1 ranged from 13.00 to 17.00 rows per cob (Table 3).Minimum kernel rows cob -1 (13.00) was recorded for Check-I while, maximum kernel rows cob -1 (17.00) was observed for hybrid 1. Kernel rows cob - 1 had significant (P≤0.01)positive association with plant height (r=0.57)while, with a rest of the characters it had nonsignificant positive correlation (Table 4).Umakanth et al. and Altenbas and Algan [23, 24] also reported that kernels rows cob -1 had significant (P≤0.01) and positive association with plant height.They suggested that while doing selection yield improvement ear diameter and kernel rows ear -1 should be given more preference.100 Kernel weight Mean square values revealed significant (P≤0.01)differences among the maize hybrids for 100 kernel weight (Table 2).For 100 kernel weight among maize hybrids mean values ranged from 25.27 to 38.27 g.Minimum 100 kernel weight (25.27 g) was recorded for hybrid 20 whereas, maximum 100 kernel weight (35.27 g) was observed for hybrid 1 as shown in table 3. Hundred kernel weight exhibited significantly negative association with flag leaf area (r=-0.46)and non-significant but positive association with all the traits except with ear length (r=-0.09)which had non-significant negative association with 100 kernel weight (Table 4).Rahman et al. [25] also observed a positive association between ear length and 100 kernel weight.Rahman et al. and Nizam-ud-din et al. [25,26] reported that 100 kernel weight and ear length are major contributors to grain yield.

Table 1 . List of hybrids and their pedigree Hybrid Pedigree
Our findings are in conformity with Shakoor et al. [11], who also noted negative association of days to tasseling with grain yield in maize genotypes.Early tasseling could cause earlier pollen shedding and silking which ultimately affects the overall maturity period of maize crop.Days to 50% anthesis Means square values exhibited significant (P≤0.01)variationamong the hybrids for days to anthesis (Table 2).Our findings are in line with Sabiel et al. and Ahmad et al. [12, 13] who also reported highly significant variation among maize genotypes for days to anthesis.Mean values for this parameter ranged from 51 to 70 days (Table3).Earliest anthesis (51 days) was observed for Check-II while late anthesis was reported for hybrid 19 (70 days).Days to anthesis had significant (P≤0.01) and positive association with days to tasseling (r=0.92) and days to silking (r=0.91),whereas, it exhibited nonsignificant association with rests of studied traits (Table4).Our findings are in correspondence withDuvick et al. [14]who also reported a positive association of days to anthesis with days to anthesis silking interval, plant height, and 100 kernel weight.