Legume Genomics and Genetics 2025, Vol.16, No.6, 297-312 http://cropscipublisher.com/index.php/lgg 305 water vapor around the plants cannot dissipate, forming a high-humidity microenvironment in the field. Peas are vine crops. In the late growth period, the vines are entangled with each other. If the planting density is too high and there is continuous rain, the ventilation and light transmittance of the lower part will be extremely poor. Group closure will bring multiple adverse effects: First, the leaves in the lower part of the closed canopy can hardly receive sunlight, and the photosynthesis is weak but still consumes nutrients, becoming a net "energy-consuming" part. Not only does it not contribute to the yield, but it also competes with the pods for limited nutrients. Secondly, pests and diseases are more likely to spread in a closed environment. For example, gray mold can quickly spread between the lower branches and leaves of the closed canopy, causing large spots and mold layers. The poor ventilation of the farmland also limits the penetration effect of pesticide spraying, making it difficult to prevent and control. Third, group closure makes the lower part of the plant prone to premature aging. Many lower pods have yellowed leaves before they mature, and they can no longer provide assimilates for grain filling, resulting in an increase in barren pods. For every 10% increase in plant density, the number of days with extremely high humidity increases by 2 to 3 days. This shows that the degree of canopy closure is proportional to the high humidity state in the field. Continuous rain is equivalent to artificially creating a "dense but not ventilated" condition, and even normal density planting will produce a similar canopy closure effect. Therefore, in the case of continuous rain, we should be more vigilant about the problem of group canopy closure. The solutions include: appropriately reducing the sowing density, especially the varieties that are prone to leggy growth should be sown reasonably sparsely to avoid excessive competition for light between plants; the vines of peas cultivated on trellises should be straightened out in time to guide them to be evenly distributed; clearing ditches and draining water in time after rain to reduce field humidity; and artificial pruning and topping can be carried out when necessary to improve ventilation and light transmittance. Foreign studies have suggested that the row closure time can be delayed by increasing the row spacing, so as to maintain good ventilation conditions for a longer period of time. Some domestic regions have also begun to adopt the "peak sowing" technology to make the peas grow unevenly to form a ladder structure that is conducive to ventilation. In disaster-resistant agriculture, these are experiences worth promoting, which can alleviate the adverse effects of group canopy closure caused by continuous rain on the pod setting rate of peas to a certain extent. 6 Preventive Strategies and Field Management 6.1 Proper plant spacing and resistance cultivar combinations In view of the adverse effects of continuous rain on peas, agricultural production should first adopt strategies from variety selection and planting layout. Different varieties have significant differences in pod-setting performance under low light and high humidity conditions, so the reasonable matching of stress-resistant varieties is a basic measure for disaster prevention and mitigation. In areas with frequent continuous rain, pea varieties with strong shade and humidity tolerance and good disease resistance should be given priority. For example, in the rainy mountainous areas in the southwest, varieties with thick stems that are not easy to fall and resistant to gray mold can be selected; while in the rainy and flood-prone areas in the north, varieties with developed waterlogging-resistant root systems can be selected. Some bred stress-resistant pea varieties need to be demonstrated and promoted to let farmers recognize their value. In terms of variety matching, a combination of "main planting + auxiliary planting" can also be adopted. While planting the main varieties in large areas, a certain proportion of shade-tolerant varieties can be intercropped or surrounded. Once the continuous rain seriously affects the main varieties, the auxiliary shade-tolerant varieties can still partially set pods to achieve risk dispersion. In addition, staggered sowing dates are also part of variety matching. For example, early, medium and late maturing varieties can be selected for sowing in stages to avoid all peas being in the flowering period at the same time and collectively suffering from continuous rain. Reasonable close planting is also an important means to deal with continuous rain. Usually, for high yields, people tend to plant at a higher density, but in areas or seasons prone to continuous rain, appropriately reducing the density can reduce the degree of group closure (Gawłowska et al., 2022; Kumar et al., 2022). It is generally recommended to reduce the sowing amount by 10%~15% compared with the usual amount to ensure ventilation and light transmission between plants. Especially for peas, which are legumes, if the density is too large, they are very likely to entangle with each other and fall
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