Stem canker pathogen inhibits poplar leaf photosynthesis in the early stage of inoculation.

Fungal pathogens can induce canker lesions, wilting, and even dieback in many species. Trees can suffer serious physiological effects from stem cankers. In this study, we investigated the effects of (. ) on () leaves photosynthesis and stomatal responses, when stems were inoculated with the pathogen. To provide experimental and theoretical basis for preventing poplar canker early. One-year-old poplar stems were inoculated with . using an epidermal scraping method. In the early stage of . inoculation (2-14 days post inoculation, dpi), the gas exchange, stomatal dynamics, hormone content, photosynthetic pigments content, chlorophyll fluorescence parameters, and non-structural carbohydrate (NSC) were evaluated to elucidate the pathophysiological mechanism of . inhibiting photosynthesis. Compared with the control groups, . noteworthily inhibited the net photosynthetic rate ( ), stomatal conductance ( ), intercellular CO concentration ( ), transpiration rate ( ), and other photosynthetic parameters of poplar leaves, but stomatal limit value ( ) increased. Consistent with the above results, . also reduced stomatal aperture and stomatal opening rate. In addition, . not only remarkably reduced the content of photosynthetic pigments, but also decreased the maximum photochemical efficiency ( / ), actual photochemical efficiency ( ), electron transfer efficiency (ETR), and photochemical quenching coefficient ( ). Furthermore, both chlorophyll and were positively correlated with . In summary, the main reason for the abated under stem canker pathogen was that . not merely inhibited the stomatal opening, but hindered the conversion of light energy, electron transfer and light energy utilization of poplar leaves. In general, the lessened CO and would reduce the synthesis of photosynthetic products. Whereas, sucrose and starch accumulated in poplar leaves, which may be due to the local damage caused by . inoculation in phloem, hindering downward transport of these products.