Genetic variability, heritability, and correlation of hybrids maize agronomy characters adaptive to dry land, medium plains

The selection of hybrid maize plants that adapt to dry land in the medium plains is very important considering the very widely available such land in Indonesia, so the existence of adaptive varieties is needed. Information on agronomic characters of adaptive hybrid maize is the basic information for character selection to make the breeding program more effective. The study aims to determine the genetic variability, heritability, and correlation of hybrid maize agronomic characters tested in dry land of medium plains. The genetic material used 22 maize hybrids, arranged in randomized block design with 3 replications. The experiment was carried out in Polewali Mandar Regency, West Sulawesi from June to September 2021. The results showed the characters that were strongly influenced by the environment were ear position height, stem diameter, male and female flowering time, and shelling percentage. The characters of stem diameter, male and female flowering time, and shelling percentage can be used for selection characters in the advanced generations. The characters that had significantly positively correlated with yield characters were plant height, leaf width, ear diameter, harvested ear weight, and weight of 1000 kernels, while the character that had negatively correlated with yield was kernel moisture content.


Introduction
Corn is a multifunctional food crop whose needs are very large for food, feed, and industry, but the high demand for corn is not matched by high national production in Indonesia [1].The low national corn production is influenced by several factors, including the use of suboptimal lands, which are often hit by drought [2].The availability of dry land in Indonesia is 68% [3], and some are located in the medium land, the land utilizes rainfed irrigation sources while corn plants per production cycle normally require between 400 -600 mm of water [4] and still the lack of dryland adaptive varieties [5] have been released in Indonesia.Therefore, hybrid corn that is adaptive to the midlands and drought tolerant and has highyielding potential is an alternative to increase maize productivity in Indonesia.
The main requirement for assembling varieties that are adaptive in the medium plains, drought tolerant and high yielding is to test these varieties in the target environment.Selection in the target environment will be successful if the characters observed show wide variability values.High genetic diversity is very useful for the conservation of germplasm and the improvement of varietal characters in the future through direct selection [6].Genetic diversity can describe variations between individuals in a population [7] [8].Heritability is an illustration of the size of the genetic contribution to a character.A high heritability predictive value indicates that genetic factors play a greater role than environmental factors, while a low heritability predictive value is the opposite [9] [10].Heritability is an important parameter in maize plant breeding.Information about genotypic and phenotypic correlations between plant traits is also needed in planning a breeding program [11].This important information is useful to shorten the selection time.Correlation is a method of determining the closeness of one character to another [12].Studying genetic and phenotypic diversity, heritability and correlation between characters of a plant population is very important for increasing the efficiency of maize plant breeding [13] especially for the specific environment.
The purpose of this study was to determine the components of genetic diversity that most influenced the agronomic characteristics of hybrid corn and to determine the heritability value caused by environmental variation and genetic variation of hybrid maize plants and the correlation between the characters on dry land, medium plains.
The experimental treatments were arranged in a randomized block design repeated three times with a plot size of 3 m x 5 m with a spacing of 75 cm x 20 cm, 2 kernels were planted in each hole, and after growing the plants were thinned and 1 plant per planting hole was left.The first fertilization was carried out when the plants were 10 days after planting (DAP) with Urea and Phonska at a dose of 150 kg and 300 kg/ha, respectively.The second fertilization was carried out at 30 HST with Urea at a dose of 200 kg/ha.Plant maintenance which includes irrigation, growth hormone spraying and pest, disease and weed control is carried out optimally.Sampling observations in the two medium rows of the experimental plot.The observed characters were plant height, ear height, stem diameter, leaf angle, leaf length and width, male and female flowering time, plant aspect, ear aspect, ear closure, ear length and width, number of rows of kernels, number of kernels per row, harvest ear weight, harvest water content, weight of 1000 kernels and yield.The yield is calculated based on the formula: Shelling Percentage (%) = Weight of 10 ears -Weight of 10 cobs Weight of 10 ears Corn yields at 15% harvest kernel moisture content are presented in units of ton/ha using the formula: Yield (t/ha) = 10.000x 100 -WC x B x R ÷ 1.000 HA (100 -15) HA = Harvested area (m 2 ), WC = kernel water content at harvest (%), B = Wet ear weight (kg), R= Shelling percentage and Y=Yield (%).Genotypic and phenotypic diversity values were derived from analysis of variance [14], as presented in Table 1.  1, the genotypic and phenotypic variances can be calculated using the formula: Heritability value in a broad sense, is calculated with the following formulation H 2 = σ 2 g σ 2 p (4) The grouping of heritability values is H2 > 0.5 (high), 0.2 <H2 <0.5 (medium), and H2 <0.2 (low) [15].
The standard deviation of genotypic variance is calculated based on the formula: Standard deviation of phenotypic variance: Genotypic and phenotypic diversity was grouped according to the formulation of [16][17], where: σ 2 g < 2 σ σ 2 g = narrow; σ 2 g ≥ 2 σ σ 2 g = wide, and σ 2 p<2 σ σ 2 p = narrow, σ 2 p ≥ 2σ σ 2 p = wide .Genotypic and phenotypic covariance analyzes were carried out using the PBT tools program and to determine the significance of the phenotypic and genotypic correlation coefficients between two characters was used T-Test, with the formula: r : correlation values The t values of the two characters are then compared with the t values in the table with df = n-2 and an error rate of 5% [18].

Results and discussion
Variance analysis of the hybrid maize tested on the medium plains in Table 2 showed the variation in all observed characters, except for the stem diameter, male and female flowering as well as shelling percentage.These four characters have a small ratio between Means Square (MS) genotype and MS error, so the diversity were very small, while the characters that have a very large ratio of MS genotype to MS error were ear length, ear diameter, number of kernels per row and number of row per ear.Diversity in a population can be caused by genetic or environmental factors, this study used hybrids formed from various parents, so that the differences in MS genotypes would be very significant, however, there were insignificant characters in the adaptation of plants in the medium plains, which might be due to environmental factors [19].The coefficient of variation (CV) is a value that shows the diversity in the population being tested, the smaller the percentage value, the higher and the accuracy of the selection.In this study, it was found that the CV values ranged from 1.62 -20.34% which indicated that the level of selection in this study was quite high, while the large CV was found only in the weight of the harvested ears and the yield.This showed that the data collected in the results of this experiment will be representative to provide the right conclusions to carry out selection breeding programs in the dry medium plains environment.
Selection to obtain plants that can adapt to certain environments requires a very diverse genetic resource, therefore high genetic diversity or variability is an important key in selection activities and this is determined by genetic background and characters that are special for adaptation to certain environments.Based on Table 3, the narrow genetic variation were found in the characters of ear height, stem diameter, male and female flowering time and shelling percentage.Low variability among hybrids for these characters because these characters are an ideotype characters of corn hybrids that are commonly released in Indonesia, where hybrid corn must have a moderate cob position, so it is easy to harvest and not susceptible to pests, the same and not too deep flowering time, large stem diameter to be able to support plants well and high shelling percentage.The characters of plant height, leaf angle, leaf length, leaf width, ear length, ear diameter, number of kernel rows per ear, number of kernels per row, ear weight, moisture content, weight of 1000 kernels and yields had a wide variability.The characters those have wide genetic variability will provide a great opportunity for selection to obtain superior genotypes and more effectively.The wide variability in these characters could be due to genetic and environmental factors, so to find out whether this variability is purely due to genetic factors or due to environmental influences, it is necessary to analyze both the genotypic and phenotypic variation for each character [16].Characters with different genetic and phenotypic variations indicate a considerable environmental influence.In our case, the characters that have different values of genotypic and phenotypic variation are the characters of ear position height, stem diameter, flowering time and shelling percentage, the results of this study were in contrast to the results shown in lowland hybrid maize studies.The different values of genetic and phenotypic variance in the characters of ear position height, stem diameter, male and female flowering time from the results of single cross hybrid maize research in the lowlands, did not show differences between genotypic and phenotypic variance [20].The Differences in the values of genetic and phenotypic variance indicate a large role for the environment in influencing plant diversity, which means that the conditions of the land used are quite varied and also that efforts to trait improvement through selection for these characters cannot be expected to.This is also seen by the heritability values of the four characters.
The estimated value of heritability is a picture of the role of genotype or environment on the appearance of a character.Characters with high heritability values were plant height, leaf angle, length and width of leaf, ear length and diameter, rows kernel number per ear, number of kernels per row, weight of harvested ears, water content, weight of 1000 kernels and yields.The results of this study were in line with the results obtained in the maize experiment on dry land where several characters such plant height, leave number per plant, ear length, ear diameter, weight of dry ear harvested per plant and yield have high heritability values [14,21].Similar results were reported for ear lenght and plant height [22], number of kernels per row in maize number of kernel row per ear 1000 grain weight [23,24].Characters with moderate heritability values were stem diameter, male flowering time and yield, while characters with low heritability were only shown for female flowering time characters.These result in line with several researches that gain heritability for female flowering (0.22) and male flowering (0.24) [25].A low genetic variety will have a low heritability predictive value, so that this character cannot be used as a good selection character for hybrid maize in the medium plains.Characters with high heritability and variance are very well used as selection and trait characters.It seems that the characters of plant height, ear length, ear diameter, weight of harvested ear and yield are very well used for early generation selection of hybrid corn plants in dry land which often occur in the medium plains because of these characters have high heretability value and are not much affected by the environment, although these character were quantitative characters controlled by many genes, generally the influence of the environment is large because many genes interact with each other.
Knowing the heritability value of a character needs to be supported by a comprehensive study of the closeness relationship of the characters through analysis of genotypic and phenotypic correlations.A positive correlation between characters indicates that selecting one character will increase another character at the same time.Conversely, a negative correlation between characters will decrease another character while increasing another.Both types of correlation can be used for specific purposes, depending on the needs of a research activity so that it will facilitate the selection activities that will be carried out later.Table 4 showed four types of correlations between genotypic and phenotypic values, namely 1) genotypic and phenotypic correlations between characters are significant and in the same direction, 2) genotypic and phenotypic correlations are significant but in different directions, 3) genotypic correlations are significant but phenotypic correlations are not significant, and 4) genotypic correlations are not significant but phenotypic correlations are significant.In our study, we obtained 6 plant height had significant positive phenotypic and genotypic correlations with the same direction for ear position height, harvest weight, weight of 1000 kernels and yield.The genotypic correlation coefficient that is in the same direction as the phenotypic correlation coefficient will describe the effect of the expressed genotype on the phenotype, so that phenotypic correlation can be used as a basis for selection if environmental influences are not significant.Similar study obtained a positive and unidirectional correlation in the character of plant height to ear weight and yield [20]. Significant and unidirectional correlations were also found between ear position height to stem diameter, leaf length, and ear length.Between stem diameters to leaf length, ear length, and the number of kernels per row.Between Leaf length to ear length and kernels per row.Between Leaf width to male and female flowering time, ear length, number of kernels per row, harvest ear weight, and yield.The male flowering time is significantly positive correlated with the female flowering time.The ear length to the number of kernels per row.Ear diameter to the number of kernel rows per ear, ear weight, and yield.Harvested ear weight to 1000 kernel weight and yield characters, while 1000 kernel weight positively correlated genotypic and phenotypic to yield characters. Characters that are positively and significantly correlated to yield will be the priority characters to obtain high-yielding hybrids in dry, midland areas and this is only shown by plant height, leaf width, cob diameter, harvest cob weight and 1000 seed weight.These characters can be secondary characters for selection if seed yield is deemed not representative.
The present study did not find the characters that have significant genotypic and phenotypic correlations but in different directions, this means that there is no environmental influences affecting the relationship between the two characters that cause the two characters to have conflicting actions.Similar findings also happened to no significant genotypic correlations with significant phenotypic correlations, this may be due to the influence of the environment that did not greatly affect the appearance of plant characters in the field.
Significant genotypic correlations with no significant phenotypic correlations were found in the correlation between ear diameters for plant height.Ear position height for male and female flowering time, kernel number per ear and 1000 kernel weight.Stem diameter for female flowering time, harvested ear weight and shelling percentage.Leaf angle for leaf width.Leaf length for kernel row per ear and kernel water content.Male flowering time for ear length, ear diameter and kernel row per ear.Female flowering time for ear length, ear diameter and kernel row per ear time and kernel number per ear.Ear length for shelling percentage and water content and kernel number per ear for water content.Single crosses hybrid maize research reported similar findings [20].Research on wheat has the same case of significant genotypic correlation relationship but no significant phenotypic correlation, between the characters of plant height and number of tillers [26,27].This can occur in plants because of the small influence of the environment on gene expression that affects the relationship between the two characters so that it does not affect significant changes in the two characters in the field [28].

Conclusion
Maize breeding programs in medium plains of dry land are largely determined by the selection of the most effective selection characters to obtain high-yielding hybrids.The characters that were strongly influenced by the environment were ear position height, stem diameter, male flowering time, female flowering time, and shelling percentage.The characters of stem diameter, male flowering time, female flowering time, and shelling percentage can be used as selection characters in breeding programs in the advanced generations.The characters that had significantly positively correlated with yield characters were plant height, leaf width, ear diameter, harvested ear weight, and weight of 1000 kernels, while the only characters that had negatively correlated with yield was kernel moisture content.

Table 1 .
Sources of variance and components of analysis of variance and mean square estimates.

Table 4 .
The estimated value of genotypic and phenotypic correlations between agronomic characters of hybrid corn, Polewali Mandar, West Sulawesi, 2021.