Phomopsis longanae Chi infection induces changes in the metabolisms of energy and respiration in relation to longan pulp breakdown

Pulp breakdown is one of the primary symptoms of quality deterioration in postharvest longan fruit. As a pivotal pathogen, Phomopsis longanae Chi (P. longanae) leads to the spoilage of fresh longan. This work aimed to elucidate the influences of P. longanae infection on the metabolisms of energy and respiration in relation to longan pulp breakdown. Longan fruit were infected for 5 min with P. longanae at 10⁴ spores mL⁻¹, while the fruit dipped in distilled water were served as the control. These longans were stored for five days under the conditions of 28 °C and 90 % relative humidity. The results showed that, compared with the control longans, P. longanae-infected longans displayed a higher index of pulp breakdown, lower levels of ATP, ADP and EC, and lower activities of H⁺, Ca²⁺ and Mg²⁺-ATPase in the membranes of mitochondria, plasma and vacuoles. Besides, P. longanae-infected longans presented a higher respiration rate, higher activities of PGI, SDH, CCO, AAO, PPO and AOX, and higher levels of NAD and NADH, while showing lower activities of G-6-PDH + 6-PGDH and NADK, and lower levels of NADP and NADPH. These findings suggest that P. longanae infection aggravated the development of pulp breakdown in fresh longan, which was related to the reduced energy status and the enhanced respiratory metabolism.