Abstract: In order to understand the effects of stem rust on the photosynthetic characteristics of oat leaves, we selected four oat varieties (sensitive varieties Bayou 1 and Mengyan 1; insensitive varieties Bayou 18 and Baiyan 5) to examine the changes of chlorophyll content and photosynthetic parameters in oat leaves 1, 3, 5, 7 and 9 days after inoculation with stem rust fungi. The results showed that net photosynthetic rate of oat leaves increased first and then decreased after inoculation, and that the sensitive varieties increased earlier than insensitive varieties. After being inoculated with stem rust fungi for three days, leaf net photosynthetic rates of insensitive varieties were significantly increased by 20.2% and 17.9% (P<0.05). After being inoculated for five days, except for intercellular CO₂ concentration, the photosynthetic parameters of sensitive and insensitive varieties were significantly decreased. Insensitive varieties can improve plant resistance by maintaining higher net photosynthetic rate, stomatal conductance, and transpiration rate, and lower intercellular CO₂ concentration.

Key words: oat, stem rust, photosynthetic characteristics, photosynthetic pigment.