Low temperature (LT) and low illumination (LI) are common meteorological factors posing a great risk to plants. This study aimed to clarify and quantify the effects of LT, LI, and their combined stress (LTLI) on the photosynthetic physiological processes of strawberry plants during the flowering stage. The results indicated that LI stress increased Chla and b levels in strawberry plants while lowering the chlorophyll a/b ratio. In contrast, LT and LTLI stress reduced chlorophyll content. All stress conditions (LT, LI, and LTLI) decreased net photosynthetic rate, stomatal conductance, transpiration rate, the maximum photochemical efficiency of photosystem II, photosynthetic electron transport rate, and actual photochemical quantum efficiency. These stresses also raised intercellular carbon dioxide concentration, non-photochemical quenching coefficient, and levels of malondialdehyde, proline, hydrogen peroxide, and peroxide ion content. Moreover, LI stress treatment boosted the activity of superoxide dismutase, peroxidase, and catalase, while LT and LTLI stress initially raised the activity of these enzymes before it eventually declined. Importantly, the previously mentioned photosynthetic physiological parameters showed notable changes under the combined stress conditions. Ultimately, the TOPSIS model was used to quantitatively evaluate the impact levels of different stressors and treatment durations on the photosynthetic system of strawberry plants. In conclusion, the synergistic impact of LT and LI results in a reduction in photosynthetic rate and photosystem II activity, a disruption in the equilibrium of the antioxidant system, and an intensification of photoinhibition, ultimately leading to diminished photosynthetic efficiency in plants.

High temperatures significantly injure the flowering, pollination, fruit growth, and quality of plants. Photosynthesis, the fundamental process supporting plant life, is crucial. Nevertheless, the quantitative evaluation of the physiological activity of the photosynthetic system of Nanfeng tangerine (NT) plants under high-temperature conditions remains a challenge. This research utilized NT plants, a distinctive citrus variety in Jiangxi Province, as the experimental subject. The study investigated the effects of varying degrees of high-temperature stress and duration on 16 photosynthetic physiological parameters of NT plants. The study examined the impact of four varying high-temperature treatment levels (32/22 °C, 35/25 °C, 38/28 °C, and 41/31 °C) for durations of 2, 4, 6, and 8 days, respectively. Principal component analysis was utilized to identify the key indicators of photosynthetic physiological activity in NT plants, with F_v/F_m, P_max, LCP, H₂O₂, MDA, and POD being selected as key parameters. The high-temperature stress index model previously constructed was used to calculate the high-temperature stress index value of the NT plants exposed to varying degrees and durations of high temperature, in order to provide a comprehensive assessment of the photosynthetic system of NT plants under high-temperature stress. Subsequently, the high-temperature stress levels were categorized into five levels based on the calculated values: Level 0 for 0 < HSI ≤ 2, Level 1 for 2 < HSI ≤ 4, Level 2 for 4 < HSI ≤ 6, Level 3 for 6 < HSI ≤ 8, and Level 4 for HSI > 8. The research results provide valuable data for agricultural meteorological departments to carry out disaster risk zoning and risk assessment in the future.

Low-temperature freezing stress constitutes the most significant meteorological disaster during the overwintering period in the Nanfeng Tangerine (NT) production area, severely impacting the normal growth and development of the plants. Currently, the accuracy of meteorological disaster warnings and forecasts for NT orchards remains suboptimal, primarily due to the absence of quantitative meteorological indicators for low-temperature freezing stress. Therefore, this study employed NT plants as experimental subjects and conducted controlled treatment experiments under varying intensities of low-temperature freezing stress (0 °C, −2 °C, −5 °C, −7 °C, and −9 °C) and durations (1 h, 4 h, and 7 h). Subsequently, physiological and biochemical parameters were measured, including photosynthetic parameters, chlorophyll fluorescence parameters, reactive oxygen species, osmoregulatory substances, and antioxidant enzyme activities in NT plants. The results demonstrated that low-temperature freezing stress adversely affected the photosynthetic system of NT plants, disrupted the dynamic equilibrium of the antioxidant system, and compromised cellular stability. The severity of freezing damage increased with decreasing temperature and prolonged exposure. Chlorophyll (a/b) ratio (Chl (a/b)), maximum quantum yield of photosystem II (F_v/F_m), soluble sugar, and malondialdehyde (MDA) were identified as key indicators for assessing physiological and biochemical changes in NT plants. Utilizing these four parameters, a comprehensive score (CS) model of freezing damage was developed to quantitatively evaluate the growth status of NT plants across varying low-temperature freezing damage gradients and durations. Subsequently, the freezing damage grade index for NT plants during the overwintering period was established. Specifically, Level 1 for CS ≤ −0.50, Level 2 for −0.5 < CS ≤ 0, Level 3 for 0 < CS ≤ 0.5, and Level 4 for 0.5 < CS. The research results provide valuable data for agricultural meteorological departments to carry out disaster monitoring, early warning, and prevention and control.

The mandarin is an important fruit crop worldwide, and ‘Xinyu mandarin’—a local Citrus reticulata variety—is widely cultivated in Jiangxi Province, in China. Autopolyploidy has frequently been used for the improvement of crop varieties. In a previous study, we identified a tetraploid (4X) material of ‘Xinyu mandarin’ generated from its diploid (2X) mother seedling via a spontaneous mutation. However, the physiological and metabolic variations after polyploidy are not clear enough, which is not conducive to the early screening. In the present study, we analyzed the morphological, physiological, and metabolic differences between the tetraploid and diploid plants. The tetraploids had larger and thicker leaves, and the activities of key enzymes in photosynthesis, the total chlorophyll, phenolic, and proline contents, were all higher in tetraploids. In the non-targeted metabolomic profile, a total of 522 metabolites were identified, of which 61 were significantly different between diploids and tetraploids. The differential metabolites included similar proportions of primary and secondary metabolites, and most of these were up-regulated in tetraploids, especially stress-related metabolites such as phenolic acids, flavonoids, alkaloids, and so on, indicating that tetraploids may possess better stress tolerance ability and vigor. Therefore, the tetraploids of ‘Xinyu mandarin’ may serve as an excellent female parent for the improvement of citrus varieties.

To clarify the genetic background and biological characteristics of grape germplasm resources and provide theoretical support for germplasm innovation and new-variety breeding, we conducted systematic morphological identification and SSR molecular-marker analysis on 38 core grape germplasms (29 fresh-eating cultivars, 1 local cultivar, and 8 wild germplasms) from the National Southeast Mountainous Crop Germplasm Repository (Jiangxi·Yichun) and other regions. For morphological identification, 14 quantitative traits and 5 descriptive traits of leaves, floral organs and fruits were determined in strict accordance with the NY/T 2932-2016 Descriptors for Grape Germplasm Resources. For SSR molecular-marker analysis, eight pairs of internationally universal core primers were used for PCR amplification and fluorescence detection referring to the NY/T 3640-2020 Identification of Grape Cultivars Using SSR Markers, and genetic diversity analysis was conducted on 11 local and wild grape germplasms. The results revealed abundant phenotypic diversity among the tested germplasms: the functional leaves of cultivars were predominantly pentagonal and cuneate, while those of wild germplasms were mostly reniform and cordate, with 3–5 lobes for most germplasms; all germplasms were hermaphroditic, except for two wild accessions with unisexual flowers. Significant variations were observed in fruit traits, with the coefficient of variation (CV) of cluster weight and berry weight reaching 67.64% and 50.53%, respectively. The genetic plasticity of weight-related traits was much higher than that of shape- and length-related traits, and the average Shannon–Wiener index (H′) of 19 morphological traits was 3.47, indicating a high level of overall phenotypic diversity. SSR analysis showed that the eight primer pairs amplified a total of 42 genotypes (5.25 per primer pair on average). The population had a mean observed number of alleles (Na) of 5.28, a mean effective number of alleles (Ne) of 7.25, and a mean polymorphism information content (PIC) of 0.74, demonstrating rich genetic diversity and high polymorphism of the tested loci. Cluster analysis divided the 11 local germplasms into four groups, which clearly reflected the genetic relationships among them, and genetic admixture was found in some germplasms due to unclear introduction traceability. In this study, fresh-eating grape cultivars suitable for the climatic conditions of Jiangxi Province were screened, the utilization value of local germplasm resources was clarified, and a two-dimensional evaluation system based on phenotypic traits and SSR molecular markers was constructed. The findings provide basic data and a scientific basis for the precise evaluation, elite gene mining, and new-variety breeding of grape germplasm resources in Jiangxi Province.

Low temperature and low irradiance (LTLI) stress severely limits strawberry growth and productivity during winter protected cultivation. This study investigated the physiological responses of the short-day strawberry cultivar ‘Benihoppe’ to individual and combined LTLI stress and developed a quantitative damage evaluation index. Seedlings were exposed to four treatments for 20 d: control (25/15 °C, 600 μmol m⁻² s⁻¹), single low temperature (LT: 15/5 °C), single low irradiance (LI: 100 μmol m⁻² s⁻¹), and combined stress (LTLI: 15/5 °C, 100 μmol m⁻² s⁻¹). Compared to isolated stress factors, combined LTLI treatment exhibited a statistically verified synergistic damaging effect (two-factor ANOVA, LT × LI p < 0.01) on leaf structure and function. LTLI-treated plants showed severe reductions in leaf area, palisade tissue thickness, chlorophyll content, and net photosynthetic rate (Pn), alongside elevated malondialdehyde (MDA) accumulation. Chlorophyll a fluorescence (OJIP) analysis revealed that LTLI stress strongly blocked the electron transport chain at the PSII acceptor side, increasing the J-step relative variable fluorescence (Vj) and suppressing the performance index (PI). To quantify these impacts, a Low Temperature and Low Irradiance Damage Index (LTLDI) was derived from 12 core physiological and morphological variables. The LTLDI scores demonstrated that LTLI induced severe damage by day 10 (score: 0.69) and extremely severe damage by day 20 (0.87), which were substantially higher than the damage caused by LT (0.58 at 20 d) and LI (0.63 at 20 d) alone. The index reliability was confirmed by its strong correlation (r > 0.9) with key stress markers (Fv/Fm, Pn, and MDA). Overall, combined LTLI stress exacerbates structural degradation and PSII photoinhibition in strawberry leaves. The proposed LTLDI offers a practical, standardized tool for evaluating stress severity, facilitating timely environmental management in greenhouse strawberry production.