Excessive nitrogen (N) application may induce powdery mildew (PM) in perennial grasses, but the resistance mechanisms to PM remain unclear. This study evaluated the physiological and molecular mechanisms of PM resistance affected by N supplies in Kentucky bluegrass (Poa pratensis L.). Cultivar ‘Bluemoon’ (N tolerant) and ‘Balin’ (N sensitive) were treated with low N (0.5 mM), normal N (15 mM), and high N (30 mM) for 21 d in a greenhouse. With increasing N levels, the disease growth was more severe in ‘Balin’ than in ‘Bluemoon’. RNA-seq and weighted gene coexpression network analysis revealed that the PpGS1.1 gene encoding glutamine synthetase was a potential hub gene for PM resistance after comparisons across cultivars and N treatments. The N metabolism pathway was connected with the plant-pathogen interaction pathway via PpGS1.1. The expression of PpGS1.1 in rice protoplasts indicated that the protein was located in the nucleus and cytoplasm. Overexpression of PpGS1.1 in wild type Kentucky bluegrass increased carbon and N contents, and the transgenic plants became more susceptible to PM with a lower wax density. The most differentially expressed genes (DEGs) for N metabolism were upregulated and DEGs for fatty acid metabolism pathway were downregulated in the overexpression lines. The results elucidated mechanisms of PM resistance in relation to N metabolism in Kentucky bluegrass.

Fodder soybean (Glycine max L.) with high protein and yield is a popular forage grass in northeast China. Seasonal drought inhibits its growth and development during seedling stage. The objective of this study was to observe morpho-physiological changes in fodder soybean seedlings under melatonin (MT) treatments and identify appropriate concentration to alleviate the drought damage. Two varieties commonly used in northeast China were treated with 0, 50, 100, and 150 μM melatonin at soil water content of 30%. The results indicated that applying melatonin enhanced height, biomass and altered root morphology of fodder soybean seedlings under water-deficient conditions. The treatments with melatonin at different concentrations significantly reduced the contents of H₂O₂, O₂⁻ and MDA, while boosting the capacity of the antioxidant defense system and the content of osmotic adjustment substances. Meanwhile, increases in light energy capture and transmission efficiency were observed. Furthermore, treatment with melatonin regulated the expression levels of genes associated with photosynthesis and the antioxidant defense system. Notably, 100 μM melatonin treatment produced the most favorable effect in all treatments under drought conditions. These research results provide new information for enhancing the drought tolerance of fodder soybean using chemical measures.

The fodder soybean (Glycine max) is an excellent leguminous forage with a high protein content and hay yield, cultivated comprehensively in alpine regions, but seasonal drought in northern regions severely impacts the growth of seedlings. Melatonin (MT) and strigolactone (SL) are critical in relieving the restraint of plant growth in water-deficient environments, but the mechanisms of MT- and SL-mediated drought resistance in fodder soybean needs to be explored. This study mainly investigated the potential morphophysiological mechanism of MT and SL treatments in protecting fodder soybean from drought stress. The fodder soybean ‘Gongnong 535’ was treated with 100 µM MT or 1 µM SL under normal, moderate, and severe water deficit conditions. The results showed that MT and SL treatments enhanced the plant growth parameters and stomatal aperture under drought stress. Moreover, the observed reductions in superoxide ion (O₂^.-), malondialdehyde (MDA), and relative electrical conductivity (REC), along with enhancements in the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), as well as higher levels of ascorbate (AsA), glutathione (GSH), soluble sugar (SS), soluble protein (SP), and free proline (Pro), indicated that MT and SL application effectively alleviated the oxidative damage and prevented the cell membrane disruption caused by drought stress. Additionally, MT and SL treatments improved photosynthesis and growth in fodder soybean seedlings under water stress by adjusting chlorophyll pigments, gas exchange indexes, and chlorophyll fluorescence parameters, as well as endogenous hormone levels. Simultaneously, MT and SL influenced the expression of genes associated with photosynthesis and antioxidant defenses, as well as phytohormone concentrations. Notably, the protective effect of the SL treatment was superior to that of MT in water-deficient conditions. This study contributes to further understanding the defensive mechanism of MT and SL against drought stress.

Plant–metabolite–microbe interactions play essential roles in disease suppression. Most studies focus on the root exudates and rhizosphere microbiota to fight soil-borne pathogens, but it is poorly understood whether the changes in phyllosphere metabolites can actively recruit beneficial microbes to enhance disease resistance. In this study, the differences of phyllosphere microbial communities and key leaf metabolites were systematically explored in resistant and susceptible black currant cultivars related to powdery mildew (PM) by integrating microbiome and metabolomic analyses. The results showed that the diversity and composition of microbiome changed, as highlighted by a reduction in microbial alpha-diversity and beta-diversity of susceptible cultivars. An increasing fungal network complexity and a decreasing bacterial network complexity occurred in resistant cultivar. Bacillus, Burkholderia (bacteria), and Penicillium (fungi) were identified as keystone microorganisms and resistance effectors in resistant cultivar. Metabolites such as salicylic acid, trans-zeatin, and griseofulvin were more abundant in resistant cultivar, which had a positive regulatory effect on the abundance of bacterial and fungal keystones. These findings unravel that resistant cultivar can enrich beneficial microorganisms by adjusting leaf metabolites, thus showing the external disease-resistant response. Moreover, the reduced stomatal number and increased tissue thickness were observed in resistant cultivar, suggesting inherent physical structure also provides a basic defense against PM pathogens. Therefore, resistant black currant cultivar displayed multilevel defense responses of physical structures, metabolites, and microorganisms to PM pathogens. Collectively, our study highlights the potential for utilizing phyllosphere microbiome dynamics and metabolomic adjustments in agricultural practices, plant breeding, and microbiome engineering to develop disease-resistant crops.

Understanding the differences in cool-season turfgrass responses to shade is critical for future turfgrass management and breeding for improved shade tolerance. The purpose of this study was to evaluate the shade-tolerance mechanisms of two cool-season turfgrass species in terms of turf performance, growth, and physiological characteristics. Two turfgrass species, namely, ’SupraNova’ (Poa. supina Schrad.) and ‘Lark’ (Lolium perenne L.), were subjected to 0 (CK, unshaded), 35% (LS), 70% (MS), and 92% (HS) shade, respectively. Compared with ‘Lark’, ‘SupraNova’ showed better turf quality (TQ) and turf color intensity (TCI) under shade. The total length and surface area of the roots of ‘Lark’ gradually decreased as the shade increased, while those of ‘SupraNova’ increased and then decreased with increasing shade. The chlorophyll fluorescence photochemical quenching coefficient (qP), electron transport rate (ETR), and maximum quantum yield of primary photosystem II (PSII) photochemistry (Fv/Fm) decreased significantly under HS; however, these decreases were more significant in ‘Lark’ than in ‘SupraNova’. The leaf reflectance of the two turfgrasses under shade was lower than that under CK, but the leaf reflectance of ‘Lark’ was higher than that of ‘SupraNova’ in the visible light band. The normalized difference vegetation index (NDVI) of the two grasses first decreased and then increased. The NDVI of ‘Lark’ under shade was slightly higher than that under CK. ‘SupraNova’ showed strong tolerance on the basis of malondialdehyde (MDA), hydrogen peroxide (H₂O₂), superoxide anion (O₂·⁻), and ascorbic acid (AsA) contents and superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activity. The MDA, H₂O₂, O₂·⁻, and AsA contents and SOD, POD, and CAT activity (which represent indicators) changed the most under MS. Taken together, the results indicated that the adaptability of ‘SupraNova’ to shade was better than that of ‘Lark’.

Bermudagrass (Cynodon dactylon) shade tolerance is a trait of immense importance to the turfgrass industry. However, little is known about shade tolerance of turf-type bermudagrass native to China. Additional knowledge of the mechanism of shade tolerance in bermudagrass is required to identify specific plant features that promote shade tolerance and assist breeding efforts worldwide. This study examines shade tolerance of two different bermudagrass cultivars, Yangjiang (prostrate form) and Guanzhong (upright form), which were developed in China. Each cultivar was subjected with 0, 30.4, 61.2, and 90.6% shade levels during growth and assessed for turf quality, turfgrass color intensity, biomass allocation, growth rate, antioxidant enzyme activity, leaf anatomy, and photochemical properties. Results generally demonstrated that turf quality and turf color intensity were lower in Guanzhong compared with Yangjiang on the 90.6% shade testing days. Yangjiang exhibited a less severe reduction of growth rate, leaf thickness, root to shoot ratio, and chlorophyll a to chlorophyll b ratio (Chla/b) under 90.6% shade compared with Guanzhong. Both cultivars exhibited a decrease in photochemical efficiency as determined by reduced qP, ETR, and Fv/Fm values. Photochemical efficiency was impacted less in Yangjian, and superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) enzymes activities were greater than in Guanzhong when exposed to severe shade. When exposed to 90.6% shade level, Yangjiang had better turf quality than Guanzhong as determined by morphological, anatomical, and physiological features. Breeding efforts focused on these shade tolerance features will lead to improved bermudagrass germplasm and aid turf management in shade environments.