Ethephon Improved Stalk Strength of Maize (<i>Zea Mays</i> L.) Mainly through Altering Internode Morphological Traits to Modulate Mechanical Properties under Field Conditions

Stalk strength is critical for reducing maize stalk lodging and maintaining grain yield. Ethephon has been widely applied to molding compact plant-type to reduce the lodging risk in maize production. However, there is little information on how ethephon regulates internode mechanical properties to improve maize stalk strength. Multiyear field experiments (2013&#8211;2017) were conducted to determine the effects of foliar-applied ethephon on summer maize internode morphological, chemical and mechanical characteristics. The hypothetical structural equation model was used to analyze the contribution of ethephon-induced changes of internode morphological and chemical traits to stalk mechanical strength. Ethephon significantly reduced the basal internode length, while increasing internode diameters and breaking resistance. Meanwhile, ethephon significantly increased the ratio of structural dry matter to total dry matter and the amount of structural dry matter per unit length and volume. Mechanical assays suggested that ethephon significantly altered geometric properties and increased the maximum bending moment, maximum failure force, while depressing the material properties. Furthermore, correlation and path analyses revealed strong correlations and significant contribution of internode morphological properties to stalk mechanical strength, respectively. These results support the conclusion that ethephon-induced morphology alteration played a major role in improving maize internode strength

Coupling Effects of Optimized Planting Density and Variety Selection in Improving the Yield, Nutrient Accumulation, and Remobilization of Sweet Maize in Southeast China

Low planting density and lack of density-tolerant varieties are the critical factors limiting the yield of sweet maize in Southeast China. However, there is relatively limited information about the interaction effects of plant density and variety on sweet maize in Southeast China. A two-year (2021–2022) field experiment was conducted with two sweet maize varieties (MT6855 and XMT10) and three plant densities (D1: 45,000 plants ha−1, D2: 60,000 plants ha−1, and D3: 75,000 plants ha−1). The results showed that plant density and variety had significant interaction effects on sweet maize yield and most traits. Increasing plant density significantly increased the fresh ear yield of MT6855, while it did not affect the XMT10 variety. The increase in fresh ear yield for MT6855 under D2 treatment was 14.9% and 14.0% higher than that under D1 treatment in 2021 and 2022, respectively. Meanwhile, increasing plant density significantly increased the bare plant rate and decreased the number of grains per ear of XMT10, while no sustainable changes were observed in MT6855. Moreover, we observed significantly increased pre-silking dry matter, N, P, and K accumulation across different densities in both varieties. In contrast, during the post-silking stage, the increasing plant density significantly improved the accumulation of dry matter, N, P, and K, only in MT6855 but not in XMT10. Meanwhile, harvest index, dry matter remobilization, and leaf N, P, and K remobilization of MT6855 were significantly higher than those of XMT10. Increasing plant density significantly increased N, P, and K partial factor productivity of MT6855 but did not remarkably affect those of XMT10. In addition, fresh ear yield of sweet maize was significantly and positively correlated with pre-silking, post-silking, and total N and P accumulation but had no significant relationship with leaf K remobilization across the two varieties. These results suggest that MT6855 is a density-tolerant variety of sweet maize, and optimizing planting density with a density-tolerant variety can improve the accumulation and remobilization of dry matter and nutrients, thereby improving the fresh ear yield and nutrient use efficiency of sweet maize

Optimal Plant Density Improves Sweet Maize Fresh Ear Yield without Compromising Grain Carbohydrate Concentration

It is crucial to synergistically improve the yield and quality of sweet maize by implementing precise and strategic planting methods. However, a comprehensive understanding of how increasing plant density affects the sweet maize fresh ear yield, grain-filling rate, and grain carbohydrate concentration is not fully understood. Thus, a field experiment was performed using a split-plot design in Southeast China in 2021 and 2022, involving four sweet maize varieties (MT6855 and WT2015 were compact-type varieties, XMT10 and YZ7 were flat-type varieties) and three plant densities (D1: 4.5 plants m−2; D2: 6.0 plants m−2; and D3: 7.5 plants m−2). The results showed that an increasing plant density markedly increased the fresh ear yield of sweet maize varieties (MT6855 and WT2015) over the two years. However, it did not influence the fresh ear yield of XMT10 and YZ7. Across all four varieties in 2021 and 2022, the increasing plant density decreased the sweet maize filled ear length, while it did not affect the grain soluble solid concentration and grain residue ratio. The sweet maize grain weight, the maximum grain-filling rate, and the mean grain-filling rate decreased significantly with the increase in planting density across all four varieties. However, plant density did not significantly affect the grain soluble sugar, sucrose, fructose, and starch concentrations across different varieties at most stages during the grain filling. The current study also found that the sweet maize fresh ear yield was dramatically positively correlated with ears ha−1, grains per ear, grain-filling rate, and grain starch concentration but negatively correlated with the bare plant rate. Notably, a parabolic relationship existed between the fresh ear yield and 100-grain weight. These findings suggest that optimizing the plant density, particularly with compact-type varieties, can improve the sweet maize fresh ear yield without decreasing its quality