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.

The color of an apple is an important index of its appearance quality, which affects the fruit’s marketability and value. The green variety “Granny Smith” remains green when ripe, and the pigment in the peel is mainly chlorophyll. The chlorophyll in the peel of the yellow variety “Golden Delicious” degrades as the fruit ripens. To explore the different mechanisms of chlorophyll degradation in the “Golden Delicious” and “Granny Smith” varieties, transcriptomic analysis was performed on the mature peels of both cultivars. High-quality sequences totaling 48,206,940 and 48,796,646 raw bases, as well as 9632 differentially expressed genes (DEGs), were identified. A total of 1206 DEGs were classified in 118 KEGG metabolic pathways. Additionally, 3258 transcription factors from 428 gene families were predicted, and DEGs associated with chlorophyll degradation, including MdSGR2, MdNYC1 and MdHCAR, were identified. Subsequently, the MdSGR2 gene was isolated from the mature peel of “Granny Smith” apples. Subsequent subcellular localization analysis confirmed that MdSGR2 specifically targets chloroplasts. The transient overexpression of MdSGR2 was found to negatively regulate chlorophyll degradation, leading to the inhibition or deceleration of chlorophyll breakdown, thereby maintaining green coloration in the leaves and peel. Conversely, silencing MdSGR2 positively regulated chlorophyll degradation, resulting in chlorosis in the leaves and peel. These findings offer valuable insights into the regulatory mechanism governing apple fruit coloration and lays a solid foundation for further investigation in this field.

Zinc oxide nanoparticles (ZnO NPs) have garnered increasing attention in agriculture due to their potential to enhance plant growth and nutrient use. This research investigates the concentration-dependent effects of ZnO NPs on young crabapple (Malus robusta) plants, addressing gaps in understanding how different concentrations influence plant development. A hydroponic experiment was conducted, applying foliar treatments of 200 mg L⁻¹ ZnSO₄ (S200) and 200, 500, and 1000 mg L⁻¹ ZnO NPs (N200, N500, N100). The control group (CK) was treated with deionized water (dH₂O). Growth parameters, antioxidant enzyme activity, and nutrient contents were measured to evaluate the impact of ZnO NPs on plant development and nutrient uptake. The results showed that N200 enhanced growth, increasing plant height by 22.64%, total dry weight by 49.36%, and root length by 116.07%. In contrast, N500 and N1000 induced oxidative stress, elevating H₂O₂ and MDA by 32.02~54.43% and inhibiting growth. N200 also improved nutrient uptake, increasing K, Ca, Fe, and Zn uptake fluxes by 84.92%, 112.12%, 185.15%, and 149.92%, respectively, whereas N1000 suppressed overall nutrient uptake but increased root Ca accumulation by 64.59%. These findings suggest that ZnO NPs can enhance plant growth and nutrient utilization at low concentrations, with potential implications for agricultural practices involving nanoparticle (NP)-based fertilizers.

Amino acid metabolism plays a crucial role in plant adaptation to drought stress, however, the underlying regulatory mechanisms remain elusive. Here, we identify MdALI, a glutamine amidotransferase in apple, as a new player in drought stress tolerance. Yeast two-hybrid, co-immunoprecipitation, bimolecular fluorescence complementation and split-luciferase assays demonstrate that MdALI interacts with MdMYB88. Biochemical assays confirm its glutamine amidotransferase (GATase) activity, catalyzing the conversion of glutamine to glutamate. Overexpression of MdALI enhances drought tolerance by promoting amino acid accumulation, notably glutamate and proline. Grafting experiments reveal that MdALI-overexpressing rootstocks confer improved drought resilience of grafted plants by modulating amino acid profiles. These findings uncover a GATase-mediated mechanism linking amino acid metabolism to drought tolerance and highlight MdALI as a promising target for breeding drought-tolerance apple rootstocks.

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.