aziz afarinesh

Maize is an important crop that is cultivated in many parts of the world. The evaluation of genotypes in breeding programs often faces two important challenges, the genotype × environment interaction effect for the target trait and unfavorable relationships between the target traits. Even though many methods have been offered for stability analysis, especially graphical tools and their relatively good efficiency in interpreting the results, it seems that the best linear unbiased predictions (BLUP) method estimates the means with high accuracy, especially in mixed models, in multi-environmental trails (MET). Therefore, the stability index of weighted average absolute scores (WAASB), which is estimated from the integration of the two stability methods of additive main effect and multiplicative interaction (AMMI) and best linear unbiased predictions, can be used in METs to estimate more accurately the stability of genotypes. Maize breeding programs prioritize high grain yields and earliness as important traits. The multi-trait stability index (MTSI) is a valuable tool for the simultaneous selection of multiple traits. It is estimated based on the average performance and simultaneous stability of genotypes in different traits and environments. Therefore, the current research aimed to identify stable and high grain yield maize hybrids along with the optimal level of grain moisture percentage at harvest time and days to physiological maturity using the integration of AMMI and BLUP methods with WAASB, WAASBY, and MTSI indices.

This study involved the evaluation of seven promising maize hybrids along with four commercial check varieties, including SC647, TWC647, SC704, and SC715, in maize METs based on a randomized complete block design with four replications across 10 regions (Karaj, Moghan, Shiraz, Kermanshah, Kerman, Mashhad, Dezful, Miyandoab, Jiroft, and Mazandaran) during two cropping seasons of 2019-2020. The recorded traits were grain yield adjusted at 14% moisture content, grain moisture percentage at harvest time, and days to physiological maturity. The WAASB was used to estimate genotypic stability for each genotype. It was computed from the singular value decomposition (SVD) of the matrix of best linear unbiased predictions of genotype vs. environment interaction effects generated by a linear mixed-effect model. The WAASBY index for simultaneous selection based on grain yield (Y) and stability (WAASB) was  estimated by assigning different weights to grain yield and stability. The simultaneous selection for grain yield and stability based on several traits was conducted using the scores obtained from an exploratory factor analysis (MTSI).

Based on the grain yield across 10 environments over two years, promising hybrid NO. 3 had the highest grain yield with 12.80 tons per hectare. According to the likelihood ratio test (LRT), the genotype-by-environment interaction was significant for the traits of grain yield, grain moisture percent at harvest time, and the days to physiological maturity. Therefore, BLUP analysis can be performed on these data due to the significant genotype by environment interaction. The BLUPs performed for hybrids were followed by stability analysis using the AMMI method on these BLUPs. The results indicated that the first and second components justified 27.7% and 24.6% of the hybrid by environment interaction variances, respectively. The highest predicted grain yield by the BLUP method belonged to hybrids No. 3, 2, 4, and 1, with higher than average predicted grain yields. Based on the biplot for the first principal component of the environments against the nominal grain yield, hybrids 2, 6, 3, and 1, having the lowest scores of the first principal component (coefficient b or line slope), had a negligible contribution to the hybrid by environment interaction and were distinguished stable. To enable simultaneous selection based on both grain yield and stability, the WAASBY index was estimated by integrating grain yield (Y) and the WAASB stability index. Considering the 50% contribution of each of the two grain yield and yield stability components, five hybrids (1, 2, 3, 6, and 4) showed above-average WAASBY. Among these, hybrids 1, 2, and 3 had significantly higher WAASBY than the other hybrids. All four control cultivars SC647, TWC647, SC704, and SC715 had lower-than-average WAASBY. Based on the MTSI, hybrid 3 was selected as the best hybrid. In addition, the estimated variance components by restricted maximum likelihood (REML) for grain yield indicated that 75.72% and 7.57% of the phenotypic variance were explained by the environment and GEI variances, respectively, whereas the contribution of residual variance to the phenotypic variance was 16.77%.

Based on the results, hybrid 3 (K47/2-2-1-4-2-1-1-1× MO17) was identified as a high-yielding hybrid, which can be introduced to farmers as a new superior maize hybrid. It seems that the use of the ratio of the WAASB stability index to grain yield (WAASB/Y) and the selection of superior genotypes based on the MTSI could identify hybrids with high grain yields, stability, and desirable levels of important agronomic traits.

This study was carried out in the two crop years of 2016 and 2017 at Safi Abad Research Center. The experiment was conducted as a factorial split plot in the form of a randomized complete block design with four replications. The main factor of the experiment was to cut off irrigation at three levels (control), cut off irrigation at the stage Silking and cut off irrigation at the stage Blister and the secondary factor wascycocel zero, 442.5 and 885 mg/l Micronutrients were zero, 1000 and 1500 gr/ha and control. The correlation results of the assessed traits with each other were determined, seed yield with plant height, number of seeds per cob, thousand seed weight had a significant positive correlation with hydrogen peroxidase, malondialdehyde, electrolyte leakage rate, catalase activity, peroxidase, superoxide dismutase and proline in leaves showed a significant negative correlation, the highest positive correlation was related to the number of seeds in the cob (0.893) and the highest negative correlation was from electrolyte leakage (-0.945) and hydrogen peroxide. (-0.854) was observed. The placement process of different amounts of micronutrients and cycocel was determined; So that different levels of micronutrients tend to be more towards the center; And consumption of 1000 gr/ha tends to zone III and the zone where yield and yield components are located. In general, it was found that foliar spraying with concentrations of 1500 gr/ha of micronutrients and 885 mg/l of cycocel by reducing the negative effects of stress, could be suitable treatments to increase tolerance toin corn stress at the end of the season.

In order to investigate the effect of cycocel and micronutrient consumption on yield, physiological traits, and antioxidant content of maize under low irrigation conditions at the end of the season, a split factorial experiment was carried out based on a randomized complete block design with four replications in Safiabad Agriculture Research Center in Dezful during two cropping years 2017-18 and 2018-19. The main treatment included water stress with three levels control (without water stress), water stress in female flower formation stage and water stress in grain swelling stage. Also, foliar application of cycocel at three levels of control (no use of cycocel), 442.5 ppm, and 885 ppm and three levels of micronutrient fertilizers, namely control (no fertilizer application), foliar application of 1000 g. ha-1, and foliar application of 1500 g. ha-1 were considered as the sub-factors. Results of the combined ANOVA showed that the interaction of the effects of year, stress, micronutrient, and cycocel on relative water content, proline and grain yield and also the interaction of the effects of stress, micronutrient, and cycocel on hydrogen peroxide, glutathione peroxidase, and soluble proteins were statistically significant (p≤0.01). The results also showed that the highest activity of superoxide dismutase enzyme was obtained under stress conditions at the grain swelling stage, which showed an increase by about 37% compared to the irrigation treatment under optimal conditions. Foliar application of 1500 g. ha-1 micronutrient and 885 ppm cycocel in non-stress conditions increased the average grain yield (11500 kg. ha-1) in the second year by about 85% compared to stressed condition at grain swelling stage and no application of micronutrient and cycocel. In general, to increase grain yield under optimal irrigation conditions and reduce the drop in stress conditions, growth regulators such as cycocel with a concentration of 885 ppm and micronutrient foliar application at 1500 g. ha-1 are recommended.