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Character Association and Path Analysis of Grain Yield and its Components in Maize (Zea mays L.) under Heat Stress

Globally, maize (Zea mays L.) is the third most important cereal crop, which is cultivated on nearly 197.19 million hectare of land with wider diversity of soil, climate, biodiversity and management practices with production of 1134.75 million tonnes and productivity of 5.76 tonnes per hectare (FAOSTAT, 2017). India is the sixth largest producer and the fifth largest consumer of maize in the world, grown on an area of 9.22 million hectare with production of 28.72 million tonnes and productivity of 3.12 tonnes International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 9 Number 3 (2020) Journal homepage: http://www.ijcmas.com


Introduction
Globally, maize (Zea mays L.) is the third most important cereal crop, which is cultivated on nearly 197.19 million hectare of land with wider diversity of soil, climate, biodiversity and management practices with production of 1134.75 million tonnes and productivity of 5.76 tonnes per hectare (FAOSTAT, 2017). India is the sixth largest producer and the fifth largest consumer of maize in the world, grown on an area of 9.22 million hectare with production of 28.72 million tonnes and productivity of 3.12 tonnes

ISSN: 2319-7706 Volume 9 Number 3 (2020)
Journal homepage: http://www.ijcmas.com Maize (Zea mays L.) is one of the most diversified and versatile crop grown worldwide under varied agro-climatic condition. However, a significant amount of reduction in grain yield has been reported because of heat stress. Being a complicated character that depends on multiple component traits, direct selection is in effective for grain yield. Considering these aspects, a study was conducted to determine the magnitude and extent of trait interdependency among yield and yield attributing characters under heat stress condition using forty five maize hybrids. The hybrids were evaluated by following randomized block design with two replications at EB-II section of the Department of Plant Breeding and Genetics, College of Agriculture, OUAT, Bhubaneswar during Summer 2018. Association studies revealed that, six characters viz., plant height, ear height, cob diameter, number of grain rows per cob, number of grains per row and 100 seed weight exhibited significantly positive correlation at both genotypic and phenotypic level, while anthesis to silking interval was the only trait that attained negative significant correlation at genotypic level with grain yield per plant. Path analysis indicated that plant height, ear height, number of rows per cob and 100 grain weight have positive direct effect while, anthesis to silking interval has negative direct effect on grain yield per plant. Hence, these traits in desirable direction could be relied upon for selection of genotypes in order to improve genetic yield potential of maize under heat stress condition.
per hectare (FAOSTAT, 2017). It is one of the most widely distributed crops and its expansion to new areas and environment still continuesowing to its adaptability to diverse environmental condition.
Forecasts indicate that by the year 2050, the demand for maize in the developing countries will double (Rosegrant et al., 2009 andPrasanna 2014) owing to the newly emerging food habits, livestock products as well as enhanced industrial requirements of rapidly expanding human population. Thus, in order to meet this demand, intensification of cropping system and increased productivity is the only way. However, this goal of increasing maize production and productivity has been hindered by the global climate change that includes rising temperatures, frequent heat waves, drought, floods, desertification and weather extremes (IPCC, 2009).A record drop in maize production due to heat waves has already been reported globally (Ciais et al., 2005;Van der Velde et al., 2010).It has been anticipated that growing season temperature in the tropics and subtropics will exceed even the most extreme seasonal temperatures so far, while in temperate regions, the hottest seasons on record will become the normal temperature (Battisti and Naylor, 2009). Thus a huge loss in corn production can be expected in the near future. Hence, development of heat stress tolerant maize germplasm is the need of the hour.
Selection based on grain yield is quite not reliable as yield is a complex quantitative trait that is governed by poly genes and also highly influenced by environmental factors in which the crop is grown. So selection of secondary traits associated with this complex trait is a way to achieve higher grain yield. Correlation analysis used as effective tool to determine the relationship among different traits in genetic diverse population for enhancement of crop improvement process. As more variables are included in the correlation study, the associations become more complex. In such a situation, the path coefficient analysis provides an effective means of finding out direct and indirect causes and effects of association and permits a critical examination of the specific forces acting to produce a given correlation and measures the relative importance of each factor. Thus aim of this study was to find out potential secondary traits associated with grain yield under heat stress condition in maize hybrids through correlation and path analysis.

Experimental details
The experimental material for the present study comprised of forty five maize F 1 s (Table  1) generated by crossing previously identified 15 heat tolerant double haploid lines with 3 double haploid testers collected from International Maize and Wheat Improvement Center (CIMMYT), Hyderabad, India. The F 1 s were evaluated in a randomized block design with two replications during spring, 2018 at EB-II section of the Department of Plant Breeding and Genetics, College of Agriculture, OUAT, Bhubaneswar. Each entry was sown in two rows of 4 meter length spaced at 60cm with a plant to plant spacing of 30 cm. Two seeds per hill were sown followed by thinning to maintain single plant per hill. In order to avoid the influence of moisture stress on the plants, proper care was taken by mulching the soil with paddy straw along with need based irrigation. Fertilizers were applied at the rate of 120 kg N, 60 kg P 2 O 5 and 60 kg K 2 O per hectare in the form of Urea, SSP and MOP respectively along with FYM 12 cart loads/ha and Zinc Sulphate 25kg/ha. Normal agronomic practices and plant protection measures were followed to raise a successful crop.
The flowering occurred during the month of May, wherein the maximum and minimum temperature ranged between 35-39ºC and 20-28ºC respectively, while the mean relative humidity during the flowering period was 74%.Data was recorded on five randomly selected plants from each F 1 s for twelve traits viz.,days to 50% tasseling (DT), days to 50 % silking (DS), anthesis to silking interval (ASI), days to 75 % dry husk (DDH), plant height (PH), ear height (EH), cob length (CL), cob diameter (CD), number of grain rows per cob (R/C), Number of grains per row (G/R), 100 seed weight (SW) and grain yield per plant (GY/P).The data was analyzed for estimating the correlation coefficients as described by Snedecor and Cochran, (1965) and path co-efficient analysis was carried out at the genotypic level by taking grain yield per plant as dependent variable against other measured traits as independent variables as suggested by Wright (1921) and discussed by Dewey and Lu (1959).

Results and Discussion
The phenotypic, genotypic correlation and path coefficients of twelve agro-economic traits of forty five maize hybrids were depicted in table 2 and table 3 respectively. The correlation coefficients were found to be significant at both genotypic and phenotypic level for most of the character combinations. In majority of the cases, genotypic correlation coefficient was higher than phenotypic correlation coefficients. Grain yield per plant was observed to have significant positive genotypic and phenotypic correlation with plant height ( , Najeeb et al., (2009) and Nemati et al., (2009). Anthesis to silking interval was the only character that exhibited significant negative association with grain yield per plant suggesting that the genotypes with less gap between anthesis and silking will give higher grain yield per plant under heat stress condition.  reported that selection for genotypes with reduced ASI was more effective than grain yield alone under drought stress. Days to 50% tasselling, days to 50% silking and days to 75% dry husk were positively correlated with each other whereas each one of them exhibited a non-significant negative correlation with yield per plant indicating the reverse relationship among the maturity related traits and grain yield per plant.     Khodarahmpour and Choukan, (2011), Pavan et al., (2011) and Begu et al., (2016. It is worth to note that cob diameter and number of grains per row recorded negative direct effect, but positive correlation with grain yield per plant. The positive correlation might arise due to high positive indirect effects via plant height. Thus in maize hybrids, tall stature was associated with better yield and might be taken into consideration for further studies under heat stress. This finding is in accordance with Al-Tabbal and Al-Fraihat (2012). Ear height possessed very less positive direct effect but significantly high positive correlation with grain yield per plant. This result is supported by Khodarahmpour (2012), who suggested that tall plants with high ear placement gave better yield under heat stress. Anthesis to silking interval is the only character that exhibited negative correlation and also negative direct effect on grain yield per plant. Such finding was also reported by . Hence, for improving grain yield, emphasis must be given for selecting genotypes with minimum anthesis to silking interval.
The results obtained from this research of character association and path coefficient analysis revealed that plant height, ear height, number of rows per cob, and 100 seed weight in positive direction and anthesis to silking interval in negative direction have significant influence on grain yield per plant in maize under heat stress condition. Thus selection for these characters can be considered as important criteria in improving grain yield of maize under heat stress.