Apple canker disease, also named as apple Valsa canker, is one of the most destructive diseases for apples (Malus domestica Borkh.). Cytospora/Valsa spp. are the dominant causal agent of this disease, but many studies have revealed that fungi from some other genus can also cause typical apple canker symptoms. In this study, we performed fungal pathogen isolation from cankered ‘Fuji’ apple barks. Six representative morphologically different fungi (Strain 1–6) were further subjected to ITS sequencing and evolutionary analysis. Molecular identification results revealed that Strains 1–6 are Cytospora mali, Fusarium cf. solani, Alternaria alternata, C. mali, Diplodia seriata and F. proliferatum, respectively. All these fungi have been reported to be causal agents of apple diseases. By inoculating fungal plugs onto trunks of ‘Fuji’ apple trees, the pathogenicity of the six fungi were accessed. Only the inoculations of the two C. mali strains (Strain 1 and Strain 4) and the A. alternata strain (Strain 3) resulted in typical apple canker symptoms in trunks. It is worth noting that Strain 1 caused much more severe canker symptoms and higher pathogenicity incidence than the other two fungi. A. alternata has been identified as a pathogen causing diseases on apple fruits and leaves. By further assessing its pathogenicity on apple fruits and leaves, we verified that it can also cause typical fruit rot and leaf spot symptoms. To the best of our knowledge, this is the first report on apple canker disease caused by A. alternata in China. Our present study can provide a theoretical foundation for the prevention and control of apple canker disease.

Combining leaf gas exchange with chlorophyll fluorescence, this study quantified the effects of soil water content (SWC) on mesophyll conductance (g_m) and biochemical parameters in 8-year-old pear trees across three soil textures [clay (CS), sandy (SS), loam (LS)], each subjected to three irrigation levels (100%FI, 75%FI, 50%FI). Results showed that SWC differed significantly, with CS > LS > SS, and that the difference in SWC in loam soil was the most obvious among different irrigation levels. The leaf water content (LWC) of SS was higher than that of LS and CS, and SS_50%FI showed 7.53% and 13.30% greater LWC compared to LS_50%FI and CS_50%FI, respectively. Specific leaf area (SLA) peaked at CS_75%FI and SS_100%FI. Soil texture and irrigation level had significant interactive effects on g_m, the product of light absorption coefficient and light energy partitioning ratio (α·β), leaf apparent CO₂ compensation point, dark respiration rate under light, and photosynthetic biochemical parameters. Differences in the values of α·β among the nine treatments were significant and the maximum values in the three soil textures were 0.660 (LS_75%FI), 0.366 (SS_100%FI) and 0.462 (CS_50%FI), respectively. The most sensitive treatment of g_m, responding to photosynthetically active radiation (PAR), was SS_100%FI and the maximal g_m under saturated PAR reached 0.271 molCO₂·m⁻²·s⁻¹, increasing 2.2-fold and 8.8-fold compared to that of SS_75%FI and SS_50%FI, respectively. An underestimation of 26.4% to an overestimation of 30.3% for g_m and an underestimation of 28.8% to an overestimation of 15.5% were observed for biochemical parameters if the empirical value (0.425) of α·β was adopted. Our findings indicated that the maximum leaf g_m could be obtained at 75%FI for loam soil, 100% FI for sandy soil, and 50% FI for clay soil, respectively.