Molecular Plant Breeding 2025, Vol.16, No.4, 211-220 http://genbreedpublisher.com/index.php/mpb 217 observe the impact of these treatments on pollination synchrony and seed setting rate. High density will cause the filaments to emerge more slowly, but most of the filaments can still be exposed within five days after spinning. If all the filaments are pollinated at one time at this point in time, it is called “simultaneous pollination treatment”. This approach significantly increased the number of kernels and the filigree setting index per plant. At low density, the number of kernels in the secondary panicles increases most significantly, with an increase ranging from 39% to 535%. At high density, mainly the number of kernels in the main panicle increased by 8% to 31% (Parco et al., 2022). In addition, the sowing time has little effect on the synchronization of the flower organs inside the spike, but there are significant differences among different varieties. Varieties with more tillers have more uniform development between spikes and less loss of flower organs at the spike tips. 8.3 Kernel yield, quality, and breeding implications Simultaneous pollination can directly increase kernel count and yield, and the effect is particularly obvious in low-density planting and varieties with many tillers (Parco et al., 2022; Rotili et al., 2022). Under high density, some superior varieties can achieve faster kernel filling and higher yield by enhancing the “source-reservoir relationship”, that is, improving photosynthesis and material transport efficiency (Ren et al., 2022). In addition, the combination of pollination synchronization with techniques such as male sterility and cross-pollination can further increase the kernel quantity, oil content and total yield, providing new management tools for growers (Westgate et al., 2022). When breeding, if the tillering ability, the synchrony of development between ears and the high-density adaptability can be taken into account, it will be easier to breed new varieties of glutinous maize with high and stable yields. 9 Challenges and Research Gaps 9.1 Climate variability and prediction models for flowering synchrony The annual climate change and seasonal temperature difference have a significant impact on the flowering time and pollination synchronization of maize. These factors will eventually affect the kernel quantity and total yield (Amas et al., 2022). However, at present, few studies have incorporated these climate changes into pollination synchronization prediction models. Especially now that extreme weather is becoming increasingly common, we still lack flowering prediction tools that can cope with different sowing periods. Moreover, many studies have only focused on a certain region or a certain year, and the universality and adaptability of the models are not strong enough (Liu et al., 2023). 9.2 Limitations in density-specific breeding lines Although increasing planting density can lead to a higher yield per mu, different maize varieties have different adaptations to density (Ghețe et al., 2021). At present, there are still relatively few specialized varieties that are highly adaptable to high-density or low-density environments. Especially for glutinous maize, the progress of genetic improvement in enhancing multi-spike ability and filamentary synchrony is still relatively slow (Omar et al., 2022; Parco et al., 2022). In addition, some breeding materials are very unstable at different densities and are not suitable for use in diverse planting methods. 9.3 Standardization of phenological measurement approaches Nowadays, the standards used in observing pollination synchrony and kernel development vary from place to place. Some look at when the filaments emerge, some look at the flowering time, and some look at the number of kernels. The recorded time points are not uniform. This leads to the fact that the results of various experiments are difficult to compare directly and the research conclusions are not easy to generalize. Especially in maize with multiple panicles or tillers, the measurement criteria for main panicles and lateral panicles are currently unclear (Parco et al., 2022). In addition, there is no efficient automatic monitoring technology at present, which leads to relatively low data collection efficiency in large-scale trials (Omar et al., 2022). 10 Concluding Remarks Whether pollination is synchronized will directly affect the seed setting rate and the number of maize kernels. If pollination can be synchronized, the number of kernels in both the main and secondary ears will increase significantly. Especially when the seeds are not planted so densely, the increase in the number of kernels in the
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