荔枝霜疫霉游动孢子及卵孢子生物学特性研究

Biological Characteristics of Zoospore and Oospore of Peronophythora litchii

为了更深入理解荔枝霜疫霉在果园内侵染流行规律．利用植物病理学方法．通过离体培养研究了环境因素对荔枝霜疫霉游动孢子释放、萌发及卵孢子萌发的影响。结果表明，在荔枝果肉培养基中，孢子囊萌发的温度等于或小于孢子囊形成的温度时．孢子囊主要以释放游动孢子的方式萌发．28℃是荔枝霜疫霉孢子囊释放游动孢子的临界温度。荔枝霜疫霉在荔枝果肉培养基中，于26℃下培养7d后，游动孢子释放最适温度范围为12～20℃，最适pH值为5～7；游动孢子萌发的最适温度为20～24℃，最适pH值为7-9；孢子囊在水滴中才释放游动孢子．游动孢子在水滴中方可萌发。荔枝霜疫霉在荔枝果皮和叶片煎汁培养基中均可产生卵孢子。当温度为28℃，pH值为5，12h光暗交替光照时，卵孢子的萌发率最高，可达到49．68％；温度是影响孢子囊萌发和萌发方式的主要因素．水是游动孢子释放和萌发的必要条件。卵孢子广泛存在于果园中，为翌年初侵染源：荔枝霜疫霉主要以游动孢子再次侵染寄主．

In order to understand how Peronophythora litchii spread in litchi orchard, the biological characteristics of zoospore and oospore germination were investigated in vitro by phytopathological research methods. Different means of germination by sporangia were determined by using temperature gradients. If the germinating temperature of sporangia was equal to or below the culture temperature, the sporangia germinated as releasing the zoospores. No zoospores were released if P. litchii was kept at 28 ℃ or higher. When P. litchii was cultured at 26 ℃ on 20% litchi flesh agar, the optimal temperature for zoospore release was 12-20 ℃ and the optimal pH was 5-7. The optimal temperature for zoospore germination was 20-24 ℃ and the pH was 7-9. Release of zoospores by sporangia and germination of zoospores relied on the availability of water. The oospores of P. litchii could generate in a juice medium of the litchi pericarp and leaf. The highest germinating rate of oospores was 49.68% which was achieved under optimal conditions at 28 ℃, pH 5 and 12 h alternating illumination. Oospores throughout the litchi orchard are a source of primary inoculum of P. litchii. Rainfall, night and morning dew in the litchi orchard is conducive to zoospore colonization and infection host.