Abstract
Increasing planting density is the main method and key management to enhance the grain yield. Preventing lodging and premature senescence in high planting density, and screening and enhancing the density-tolerance of maize variety is the main goal of agronomy. Differential response of maize hybrids to high plant density greatly affect the dry matter accumulation and its allocation to maize kernel, depending upon various traits responsible for crowding stress tolerance, of which ear characteristics are pivotal. Density resistance as a quality appraisal of certain variety permits the construction of a simple and accurate method to determine this value, useful for plant breeding. Therefore, we created a new quantitative method, which tested several maize varieties planted populary in China (e.g. Zhengdan 958, Xianyu 335, and Denghai 661) to quantify their response to crowding stress through model. We established 13 planting densities (ranging 1.67–16.67 plants m−2) by adopting fixed line spacing (80 × 40 cm) and then gradually increasing row spacing from 1 m to increasing planting density. A conventional standard plot was also established for verification and evaluation of the plant morphologic characteristics, ear traits, and the yield of maize at various standard densities during 5-year study period. By studying the density–yield relationship, a quantitative model was constructed to identify the density resistance of maize. Grain yield of maize varieties under varying planting densities were simulated, and models of population yield and yield per plant that fitted the data well with high biological significance were produced. From the models, the optimal density of the popular main maize varieties planted in China and the morphological characteristics of each variety at that density were identified. The density-resistance of each variety was referred to as the ear-sensitivity classification. With the highest yield at the optimal density, the plant height of each variety reached 98% to that of tallest plant. The ear/plant ratio was about 0.45, and the ratio between the stem diameter and the largest stem diameter was 0.65–0.80. During the harvest period, the ratio between average single-plant yield and the highest single-plant yield was 0.40–0.50. By gradually increasing planting density, the density resistance of the maize and the changes in yield with density were quantified. Present study provides a convenient tool for the effective selection of varieties by plant breeders through this method and model will help to rapidly identify the density resistance for a new variety and accurate confirmation to optimal planting density, it could be optimized to enable practical production at reasonable planting densities.
Highlights
A gigantic increase of six-fold was observed in maize grain yields since the onset of hybrid era starting from 1939 to date, mainly attributed to successful breeding strategies and superior agronomic managements, amongst which the increased planting density is a prominent contributor[1,2,3]
The varieties used for testing were upright-leaf maize varieties including Xianyu 335 (XY335), Zhengdan 958 (ZD958), Denghai 661 (DH661), and spreading-leaf maize varieties including Zhongdan 808 (ZD808) and Yinong 103 (YN103)
Over the range of densities examined in the study, the population yields of the different varieties followed the order Xianyu 335 > Denghai 661 > Zhengdan 958 > Zhongdan 808 > Yinong 103
Summary
A gigantic increase of six-fold was observed in maize grain yields since the onset of hybrid era starting from 1939 to date, mainly attributed to successful breeding strategies and superior agronomic managements, amongst which the increased planting density is a prominent contributor[1,2,3]. As proposed by Tollenaar et al.[12], the maize plant accumulates its half of the total dry matter after the flowering stage, which is mainly driven by maximum light interception by additional leaf area per land area as a function of canopy photosynthesis Another important feature to this yield increment is the genetic gain through rigorous breeding strategy of increasing yield per plant by selecting hybrids of functional stay-green and with improved source-sink balance[2,13]. Crowding stress hinders to attain full genetic potential for maize crop, but progressive breeding through successful selection under dense environments has resulted in development of maize hybrids in China which can perform best under stressful environments[10,17,18] This genetic gain is associated with increased kernel number, improved post-silking biomass accumulation and better partitioning of attained dry matter to economic plant parts[10,18,19]. The motivation for this study was the urgent need to devise a method that can identify density resistance and accurately evaluate multiple crop varieties in a time- and energy-efficient manner
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