Molecular Plant Breeding 2025, Vol.16, No.4, 211-220 http://genbreedpublisher.com/index.php/mpb 215 6 Interactions Between Sowing Date and Density 6.1 Synergistic and antagonistic effects on pollination window The combination of sowing time and planting density will jointly affect the pollination synchronization of maize. Generally speaking, the higher the density, the later the filaments will appear. However, most of the filaments will still be fully exposed within five days after they are spun. If both the main spike and the secondary spike can successfully complete pollination during this period, it will significantly increase the number of fruiting kernels and the fruiting ratio of filaments per plant. In the fields where the seeds are planted relatively sparsely, the increase in the number of kernels in the secondary panicles is the most obvious. Under high density, the increase in kernels of the main panicle is more obvious. Synchronous pollination can alleviate the problems caused by the late appearance of filaments, make the coordination time between filaments and pollen more compact, and improve the pollination efficiency. 6.2 Combined influence on spikelet fertility and kernel set The coordination of sowing time and density also affects the differentiation process of spikelets at the spike, whether they can be successfully pollinated, and whether kernels can be produced in the end. Late sowing combined with high density will result in less nutrient distribution from the plant to the spikelet, making it more difficult for the spikelet of the spikelet to grow well and reducing the proportion of exposed filaments. Eventually, the seed setting rate of the spikelet will decline. However, if the density is appropriate and the sowing time is also appropriate, the spikelets of the main spike and the secondary spike can grow more uniformly together, and the fruiting will be more stable (Parco et al., 2022). Moreover, the more synchronous the pollination is, the higher the seed setting rate and quantity will be, especially when the competition for nutrients is relatively intense (Rotili et al., 2022). If the sowing time and planting density can be properly adjusted, the kernel miscarriage caused by the asynchronous development of filaments can be reduced, and the overall fruiting efficiency can be improved (Shen et al., 2019). 6.3 Management strategies based on G ×E ×M interactions There are significant differences among various maize varieties, climatic conditions and management methods (such as sowing time and planting density), so when planting, strategies can be adjusted according to the situation to make pollination more synchronized and the kernels grow better. For varieties that are prone to secondary panicles or have many tillers, if low density is used and the sowing time is appropriate, the secondary panicles can develop smoothly and produce seeds normally, which helps to improve the stability of yield (Rotili et al., 2022). However, if the density is too high or the resources in the environment are insufficient, the normal development and pollination of the main spike should be ensured first to avoid the secondary spike competing for nutrients (Parco et al., 2022). In addition, appropriately adjusting the pollination time, such as artificial synchronous pollination, can also increase the seed setting rate, especially when the density is high or the weather is bad (Westgate et al., 2022). Therefore, considering the variety characteristics, weather conditions and field management methods in combination, that is, the so-called G×E×M integrated management model, is the key to growing glutinous maize well and increasing yield and quality. 7 Physiological and Molecular Regulation of Kernel Development 7.1 Hormonal crosstalk during fertilization and early kernel growth At the beginning of kernel development, some hormones, such as auxin (IAA), abscisic acid (ABA), salicylic acid and cytokinin, play a significant role and mainly affect the differentiation process of kernels after fertilization (Zhou and Hong, 2024). Auxin can help kernels with sugar metabolism and cell division, making them more active. ABA, on the other hand, is related to the early developmental competitiveness of kernels. Studies have found that IAA can promote the expression of genes related to sugar utilization, while inhibiting the synthesis and signal transduction of ABA, thereby helping kernels develop better (Du et al., 2023; Wang et al., 2023). The relationship between hormones and sugar is also very close. The level of sugar can affect auxin synthesis genes (such as ZmYUC), and thereby affect whether the kernels grow fast or not (Doll et al., 2017). Under stress conditions such as high temperature, the reactions of IAA, ABA and salicylic acid will also change, which is very crucial for kernel development (Figure 2) (Guo et al., 2021).
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