Leaf gas exchange and chlorophyll a fluorescence in Hevea brasiliensis in response to Pseudocercospora ulei infection

South American leaf blight (SALB), the main disease found in the rubber tree crops of Latin America, is caused by the fungus Pseudocercospora ulei. This study aims to determine the photosynthetic response of two clones of H. brasiliensis with different resistances to SALB from P. ulei under controlled conditions, by means of a temporal analysis of gas exchange and chlorophyll a fluorescence. The results show that the effect on photosynthesis was proportional to the temporal progress and intensity of the disease symptoms to this effect, the maximum significant decrease (p < 0.05) in photosynthetic rates in the clone FX 3864 (susceptible) (88.3%) and in FX 4098 (moderately resistant) (45.2%) was observed 8 days after inoculation in B leaflets that were 18 days old. Meanwhile, a significant difference was found between the two clones' ability to capture, use, and dissipate light energy through photosystem II, which was evidenced by the minimum photosynthetic activity registered in the susceptible clone.