Hail, known as an agricultural meteorological disaster, can substantially constrain the growth of the apple industry. Presently, apple orchards use a variety of colored (photo-selective) hail nets as a preventative measure. However, it is unclear which color proves most effective for apple orchards. This study provides a systematic investigation of the impact of four photo-selective colored hail nets (white, blue, black, and green; with white being the control) on the microenvironment of apple orchards, fruit tree development, fruit quality, and yield over a two-year period (2020–2021). Different photo-selective nets do not evidently alter the intensity of light, although the nets’ shading effects decrease in the order from black to green to blue. Among them, blue nets increased the proportion of blue light, while green nets enhanced the proportion of green light. On the other hand, black, green, and blue nets diminished the proportion of red and far-red light. Such photo-selective nets effectively lowered soil temperature but did not have an impact on relative humidity and air temperature. Encasing apple trees with blue nets promoted growth, increasing shoot length, thickness, leaf area, and water content, while simultaneously decreasing leaf thickness. Black nets had comparable effects, although the impacts of green nets were inconsistent. Different photo-selective nets did not significantly influence the leaf shape index or overall chlorophyll content. However, black and green nets reduced the chlorophyll a/b ratio, while blue nets slightly boosted this ratio. Additionally, blue nets proved beneficial for apple trees’ photosynthesis. With the employment of a principal component analysis and comprehensive evaluation, this study concludes that blue nets offer the most favorable environmental conditions for apple growth while protecting apple orchards against hail, compared to black, white, and green nets.

MYB30-Interacting E3 Ligase1 (MdMIEL1) plays a negative role in apple (Malus × domestica) cold tolerance by mediating the degradation of its target proteins. Its protein stability decreases under cold stress; however, how MdMIEL1 is regulated under cold conditions remains unclear. Here, we report that the α-catalytic subunit of sucrose non-fermenting-1-related protein kinase, MdKIN10, a positive regulator of cold stress, interacts with MdMIEL1, leading to its phosphorylation and subsequent degradation. Specifically, cold-activated MdKIN10 phosphorylates MdMIEL1 at serine 198, which occurs near the AIM motif; this modification further enhances the interaction between MdMIEL1 and MdATG8i, thereby promoting MdMIEL1 degradation through the autophagy pathway. Furthermore, MdBBX7, which functions as a positive regulator in apple cold stress responses by positively regulating the expression of ω-3 fatty acid desaturase (MdFAD8) and C-repeat-binding factor 2 (MdCBF2), thus promoting fatty acid desaturation and cold-responsive gene expression, is a target of MdMIEL1. In addition, MdKIN10-mediated phosphorylation of MdMIEL1 at Ser198 attenuates the ability of MdMIEL1 to inhibit apple cold tolerance and decrease MdBBX7 protein abundance in response to cold stress. Our study reveals an intricate post-translational modification cascade of MdKIN10-MdMIEL1-MdBBX7 molecular module under cold stress in apple.

Drought stress represents a major constraint on global apple production, with the widely used semi-dwarfing rootstock ‘M.26’ being particularly vulnerable to water deficit. Although the osmolyte trimethylamine N-oxide (TMAO) has been shown to improve abiotic stress tolerance in the model plant Arabidopsis, its potential role in enhancing drought resilience in woody fruit trees remains largely unexplored. Under prolonged moderate drought stress, exogenous TMAO application significantly promoted plant growth, mitigating the drought-induced suppression of plant height by 5.3–12.2% compared to untreated drought-stressed controls and alleviating the decline in above-ground biomass. This improvement was underpinned by a substantial alleviation of root growth inhibition, with TMAO restoring total root length and biomass from 37% in the control to only 6.1–9.5%. TMAO also fine-tuned the root-to-shoot ratio to favor resource allocation to roots. Consequently, TMAO-treated plants maintained superior leaf water status, exhibiting higher relative water content (drought-induced reduction limited to ~17.5% with TMAO versus 26.3% in the control). Physiologically, TMAO alleviated the drought-induced stomatal limitation of photosynthesis, sustaining higher net photosynthetic rate, stomatal conductance, and transpiration rate. Crucially, under severe drought stress, TMAO pretreatment markedly enhanced ‘M.26’ survival rates from approximately 39% in the untreated control to 60–68%, representing a relative increase of approximately 74%. Collectively, this study demonstrates that exogenous application TMAO significantly enhances drought tolerance in apple rootstock ‘M.26’, highlighting its potential as an effective and environmentally safe plant growth regulator for more sustainable cultivation of fruit trees under irregular/erratic irrigation conditions.