Study on Photosynthesis of the Pecan Under the Stress of Black Spot Disease

Taking five pecan varieties with different resistance, ‘Pawnee’‘Xinxuan 4-1’‘Kanza’‘Mahan’‘Wichita’ as test materials, field test and instrumental measurement methods were used.The effects of black spot disease on the photosynthetic physiological parameters of net photosynthetic rate（Pn）,transpiration rate（Tr）,intercellular CO₂ concentration（Ci） and stomatal conductance（Gs）,and the chlorophyll relative content of the disease leaf and healthy leaf were studied in five varieties, in order to provide reference for the control of black spot disease of pecan.The results showed that black spot significantly affected photosynthesis, and the net photosynthetic rate, transpiration rate, stomatal conductance and chlorophyll content were significantly decreased（P＜0.05）.The intercellular CO₂ concentration of all cultivars except ‘Kanza’ were significantly increased（P＜0.05）,suggested that non-stomatal factors might be one of the main reasons for the decrease of photosynthesis of susceptible pecan.It was also found that the decrease range of net photosynthetic rate, transpiration rate, stomatal conductance and chlorophyll content of the resistant cultivars was lower than that of the sensitive cultivars,indicated that the resistant cultivars could delayed the damage of photosynthesis caused by black spot disease to a certain extent.