To study stability in maize (Zea mays L.) under non- stress situation

Introduction

Among the cereals grown globally, maize (Zea mays L.) ranks foremost. It is placed in the tribe Maydeae of the family Poaceae, carries 2n=20 and is native to South America. Short day in its flowering behaviour and monoecious in nature, the crop was brought under domestication about 8,years ago. Two genera stand as its close relatives, namely Tripsacum (gama grass) and Teosinte (Euchlena). Cultivation of maize extends throughout the world, and the crop has emerged as one whose genetic yield potential is the highest and whose adaptability spans widely varied agroclimatic conditions. Rising industrial requirements, together with the demand for value-added foods in a growing economy and population, indicate that maize will retain its share as a crop of consequence. Within India it ranks third among cereals for grain production, behind only rice and wheat. Its grain is directed mainly to feed, poultry, swine and fish accounting for about 52 percent and cattle about percent, while 23 percent serves as food and 13 percent as industrial raw material. In its role as a food crop the utilization pattern of maize is more diverse than that of other major crops, a consequence of the array of by-products developed from it and of the diverse types available, among them quality protein maize (QPM), sweet corn, popcorn and baby corn etc (Yadav et al., 2014) [1] . Globally the crop occupies an area of 199 million hectares, returning a production of 1129.20 million tonnes at a productivity of 5820 kg ha -1 (Anon., 2024) [2] . The Indian figures stand at 461.49 lakh tonnes of grains produced from an area of 128.35 lakh hectare, corresponding to a productivity of 3595 kg ha -1 . Karnataka accounts for 19.02 lakh hectares under the crop, from which a production of 63.51 lakh tonnes is obtained at a productivity of 3339 kg ha -1 (Anon., 2025-26) [3] . Drought and low soil fertility rank foremost among the abiotic stresses that limit tropical maize production. Rainfed conditions account for the greater part of tropical maize production, and in such areas drought is regarded as the most important abiotic constraint to production (CIMMYT 1999). Of all the limitations that keep maize from realizing its grain yield potential, drought is the most pervasive (Edmeades et al., 2001) [4] . The way a genotype reacts to environmental conditions governs the stability of its yield, and that capacity rests on the genetic composition of the genotype (Borojevic, 1990) [5] . Identifying hybrids whose interaction with environments is least therefore calls for extensive testing of maize hybrids in different environments. For yield stability to be achieved efficiently in maize improvement, heterozygosity has been reported to be a prerequisite (Becker and Leon, 1988) [6] . Working with maize, Eberhart and Russell (1969) [7] showed heterogeneous populations to possess better yield stability than homozygous ones, and observed further that two single cross hybrids were as stable as any of the double crosses while yielding higher besides. There is a need to evaluate the yield stability of maize hybrids raised from parental lines differing in their levels of tolerance to drought (Duvick et al., 2004) [8] , and (Tollenaar and Lee, 2002) [9] observed that the yield gains realised genetically over the preceding 30 years owed themselves to greater stress tolerance rather than to any increase yield per se. Knowledge of phenotypic stability serves a further purpose, being useful both for the selection of crop varieties and for the conduct of breeding programmes. Wherever a set of genotypes (cultivars) is evaluated over environments that differ widely, genotype × environment interaction emerges as a universal phenomenon. Traits of agronomic and economic importance, grain yield foremost among them, are quantitatively inherited and routinely display G × E interaction. Genotypes must consequently be evaluated over a number of environments once selection has reached its advanced stages (Fan et al., 2007) [10] . The present study, entitled " to study stability in maize (zea mays l.) under nonstress situation ", was accordingly planned and executed.

Materials and Methods

Main Agricultural Research Station, Dharwad, situated at 150 0 25' N Latitude and 70 ⁰ 25' East longitude with an altitude of 678m above mean sea level, served as the site of the present investigation, which spanned the kharif, rabi and summer seasons of 2011-12, 2012-13 and 2013-14. Appendix I furnishes the data on climatic parameters registered over the period of crop growth, namely rainfall and the minimum and maximum temperature. The Botanical garden of Main Agricultural Research Station, College of Agriculture, Dharwad, was where the experiment was carried out, during rabi and summer. Climatic parameters over the period of crop growth, namely rainfall and the minimum and maximum temperature registered, are set out in Appendix I. The weather data over the total crop growth period indicated mean minimum and maximum temperatures lying between 15.6 and 32.62 ⁰C with 56.60 mm rainfall during rabi 2011-12, while for rabi 2012-13 the temperatures ranged from 15.65 to 29.20 ⁰C with 144.50 mm rainfall, and summer 2013-14 registered temperatures from 19.50 to 35.08 ⁰C with 178.40 mm rainfall. The experiments in every season were conducted in rabi / summer, covering stress as well as non-stress situations. Eight single cross hybrids were produced during kharif 2011, and these single cross hybrids were subsequently assessed, together with five commercial checks (900M Gold, NK6240, Arjun, Bio-9681 and All-rounder), under non-stress situations in a randomized complete block design (RCBD) replicated three times. Sowing was taken up on 14.12.2011, 12.10.2012 and 08.02.2013, respectively. Each entry occupied a four row plot, 4 meter in length, at a spacing of 75x20 cm. Two seeds per hill were placed by hand dibbling and thinned out to maintain a single plant per hill during the second week after sowing (10-15 days after sowing). Besides the recommended cultural practices, the genotypes under non-stress received regular irrigation (furrow) at an interval of 10-days, so that they did not experience any stress. Five competitive plants selected at random were tagged separately. Observations on morphological traits and yield contributing traits were recorded from five randomly selected competitive plants per replication per genotype. For every character the mean value of the five observations was computed, and these means were used for stability analysis. The single cross hybrids along with the checks are listed as follows: Statistical analysis followed the procedure of Eberhart and Russell (1966) [11] and was performed in WINDOSTAT 8.0 software.

Results and Discussion

For each of the eight single cross hybrids and the five checks, the data gathered on the different character were evaluated over three years under non-stress, the object being to find out the performance of each genotype over environment.

Table gives the pooled ANOVA for stability of the different characters (Eberhart and Russell, 1966) [11] . Nine characters showed significant genotypic differences when pooled over environments, viz,. [11] , which a number of workers have applied to maize and to other crops. On the criteria of Eberhart and Russell (1966) [11] , stability in a variety implies a regression coefficient (bi) equal to one, a deviation from regression (S²di) lying as close to zero as possible, and high mean performance. For Allard and Bradshaw (1964) [12] , the selection of a stable genotype rests on the genotype having less interact with environments. The three measures named above, viz., mean, regression coefficient (bi) and the mean square deviation (S²di), were the means by which stability was assessed among the genotypes included in the present study. Response of a particular genotype may simply be measured by the linear regression (bi): a value greater than one marks the genotypes as sensitive to environment changes but adopted to favourable environments, while a value below one points to above average stability. Where the latter goes together with a high mean value, such a genotype counts as better adapted to widely differing situations for unfavourable environment, whereas a low mean value points to greater G×E interaction (Finlay and Wilkinson, 1963) [13] . Deviation around the regression line, however, ranks as the better measure of stability. Taking the non-linear component of the G×E interaction, whichever genotype carries the lowest standard deviation will prove the most stable, and viceversa. Findings of the present study with respect to stability parameter are discussed below.

When the stability parameters of the genotypes tested over environments are considered, stable performance was not attained by any of the genotypes. _ KDMI-15× NEI-9202B among them took the fewest days to anthesis to silking interval, Bio-9681 the most. Since a smaller number of days to anthesis to silking interval is the more desirable attribute, KDMI-15×NEI-9202B emerged as the ideal genotype in this respect. Regression values above unity, which point to suitability to favourable environments, were returned by the hybrids Bio-9681, CM-111×NEI-9202B 4 KDMI-15×NEI-9202B, RMH-2, NK-6240, H S-2 × NEI-9202B and Allrounder. A regression coefficient statistically below unity, coupled with non-significant S²dᵢ, was found in the hybrids Arjun, 900M, H S-4 ×NEI -9202B, NEI-9208B × H S-15, H S-15×HS-17 and CI-4×HS-4 ; ; such hybrids, having above average stability, are adoptable to unfavorable environments, or more specifically to poor environments. In CI-4×CML-446 a significant regression value again indicates suitability to favourable environments. Agreement with these findings is found in Arun and Singh (2004b) [14] , Kaundal and Sharma (2006) [15] , Nagabhushan (2008) [16] and Vijaykumar (20008). Among the stability parameters for number of cobs per plant, the genotype Arjun emerged as stable across the environments, with its regression (b i ) value statistically equal to unity and S²dᵢ approaching to zero. [17] , Nagabhushan (2008) [16] and Vijaykumar (20008), Kuchanur (2010) [18] , Romay et al. (2010) [19] and Badu-Apraku and Oyekunle (2012) [20] . As regards DSI, among the eight single cross hybrids and five checks it was the single cross hybrids viz. (H S-15 × H S-17) that returned the lowest DSI values for grain yield (kg/ ha). Findings of a similar nature have also been reported by Jafaria et al. (2009), Kuchanur (2010) [18] , Majid et al. (2010) [21] , Lata et al. (2011) [22] , Ijaz-Ul-Hassan et al.

(2011) [23] , Badu-Apraku and Oyekunle (2012) [20] , Moradi1 et al. (2012, Khalil (2013) [24] and Paulo Roberto et al.

To conclude, of the 13 single cross hybrids subjected to stability analysis under nonstress, eight proved stable across seasons, viz., Arjun, NEI-9208B × HS-15, NK6240, 900M, CI-4×HS-4 ， KDMI-15×NEI-9202B, HS-4 × NEI-9202B and HS-2 × NEI-9202B.

Conclusion

The present study demonstrated substantial variation among maize (Zea mays L.) hybrids across three seasons under non-stress conditions. Environmental effects were significant for most traits, whereas genotype × environment interaction was generally non-significant, indicating comparatively consistent hybrid performance. Significant linear environmental effects and largely non-significant pooled deviations further suggested that most responses were predictable. Among the tested entries, KDMI-15 × NEI-9202B showed desirable stability for grain yield, with a regression coefficient close to unity and minimal deviation from regression. HS-2 × NEI-9202B recorded the highest mean grain yield, while HS-15 × HS-17 exhibited the lowest drought susceptibility index. Overall, eight hybrids-Arjun, NEI-9208B × HS-15, NK6240, 900M, CI-4 × HS-4, KDMI-15 × NEI-9202B, HS-4 × NEI-9202B and HS-2 × NEI-9202B-were identified as stable across seasons. These hybrids may support cultivation and future breeding programmes targeting reliable performance under non-stress environments and variable seasonal conditions in practice.

References

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