Powdery mildew (PM) is one of the most important fungal diseases in Cucurbita moschata (pumpkin) cultivation. This experiment was conducted to shed light on the physiological mechanisms of PM resistance in pumpkin cultivars. PM pathogen was inoculated on pumpkin seedlings, PM-susceptible genotype (JJJD) and PM-resistant genotype (inbred line 112–2) to study the PM-fungal growth, plant photosynthetic and biochemical parameters with different intervals of time. The disease index and pathogen growth observed for the PM-infected 112–2 seedlings were milder than those observed for the JJJD seedlings. The net photosynthetic rate (Pn), stomatal conductance (gs) and transpiration rate (Tr) were reduced for both the PM-infected genotypes, while the internal CO2 concentration (Ci) increased in comparison with the non-infected controls. PM pathogen inoculation impaired the photosynthetic performance in seedlings of both genotypes and this was largely associated with stomatal closure. In comparison with the non-infected controls, the superoxide dismutase (SOD) and β-1,3-glucanase activities were reduced for both the PM-infected genotypes, while the peroxidase (POD) and phenylalanine ammonia lyase (PAL) activities were increased. The catalase (CAT) activity was reduced in the 112–2 genotype and increased in the JJJD genotype after PM pathogen inoculation. Together, our data show that PM resistance in pumpkin seedlings is associated with the maintenance of photosynthetic performance and the regulation of defense-related enzyme activities .

中文翻译：

---

Cucurbita moschata 基因型感染白粉病后的光合特性和生化代谢

白粉病（PM）是南瓜（Cucurbita moschata）栽培中最重要的真菌病害之一。本实验旨在阐明南瓜品种抗 PM 的生理机制。将 PM 病原体接种在南瓜幼苗、PM 易感基因型（JJJD）和 PM 抗性基因型（自交系 112-2）上，以研究不同时间间隔的 PM 真菌生长、植物光合和生化参数。观察到 PM 感染的 112-2 幼苗的疾病指数和病原体生长比观察到的 JJJD 幼苗温和。与未感染的对照相比，PM 感染的两种基因型的净光合速率 (Pn)、气孔导度 (gs) 和蒸腾速率 (Tr) 均降低，而内部 CO2 浓度 (Ci) 增加。PM 病原体接种损害了两种基因型幼苗的光合性能，这在很大程度上与气孔关闭有关。与未感染的对照相比，PM 感染基因型的超氧化物歧化酶 (SOD) 和 β-1,3-葡聚糖酶活性均降低，而过氧化物酶 (POD) 和苯丙氨酸解氨酶 (PAL) 活性增加. 接种 PM 病原体后，过氧化氢酶 (CAT) 活性在 112-2 基因型中降低，而在 JJJD 基因型中增加。总之，我们的数据表明南瓜幼苗的 PM 抗性与光合性能的维持和防御相关酶活性的调节有关。与未感染的对照相比，PM 感染基因型的超氧化物歧化酶 (SOD) 和 β-1,3-葡聚糖酶活性均降低，而过氧化物酶 (POD) 和苯丙氨酸解氨酶 (PAL) 活性增加. 接种 PM 病原体后，过氧化氢酶 (CAT) 活性在 112-2 基因型中降低，而在 JJJD 基因型中增加。总之，我们的数据表明南瓜幼苗的 PM 抗性与光合性能的维持和防御相关酶活性的调节有关。与未感染的对照相比，PM 感染基因型的超氧化物歧化酶 (SOD) 和 β-1,3-葡聚糖酶活性均降低，而过氧化物酶 (POD) 和苯丙氨酸解氨酶 (PAL) 活性增加. 接种 PM 病原体后，过氧化氢酶 (CAT) 活性在 112-2 基因型中降低，而在 JJJD 基因型中增加。总之，我们的数据表明南瓜幼苗的 PM 抗性与光合性能的维持和防御相关酶活性的调节有关。接种 PM 病原体后，过氧化氢酶 (CAT) 活性在 112-2 基因型中降低，而在 JJJD 基因型中增加。总之，我们的数据表明南瓜幼苗的 PM 抗性与光合性能的维持和防御相关酶活性的调节有关。接种 PM 病原体后，过氧化氢酶 (CAT) 活性在 112-2 基因型中降低，而在 JJJD 基因型中增加。总之，我们的数据表明南瓜幼苗的 PM 抗性与光合性能的维持和防御相关酶活性的调节有关。