Objective Leaf structure and physiology of resistant and susceptible Litchi chinensis Sonn. in response to anthracnose were compared for improved disease prevention and resistant variety breeding.

Methods Paraffin sectioned mature leaves of the resistant Haiken 5 (HK5) and the susceptible Nongmei 5 (NM5H) litchi were examined under a microscope. Wax content in the leaves was determined by chloroform extraction. Collected leaves were inoculated with Colletotrichum gloeosporioides Penz. on mycelial agar disks as treatment and on a PDA medium as control for microscopic observations with he leaves stained with aniline blue at 0, 6, and 24 h post inoculation (hpi). Activities of malondialdehyde (MDA), peroxidase (POD), superoxide dismutase (SOD), phenylalanine ammonia lyase (PAL), chitinase, polyphenol oxidase (PPO), and laccase (Lac) of the leaves were analyzed as well.

Results The structures of the HK5 and NM5H leaves were generally similar. The leaves and spongy tissue of NM5H were significantly thicker than those of HK5, and the HK5 leaves had a significantly higher wax content than NM5H. The appearances of disease spots on the leaves of HK5 and NM5H became significantly different at 24 hpi. The PAL activity rose significantly at 6 hpi, and POD at 24 hpi in HK5; PPO and Lac at 6 hpi, while POD at 24 hpi, in NM5H increased significantly; and Lac significantly increased at 6 hpi and chitinase at 24 hpi in both varieties.

Conclusion The wax content and thicknesses of leaf and spongy tissue seemed to reflect the anthracnose resistance of the litchi plants. The enzymes, such as PAL, POD, chitinase, PPO, and Lac, in the leaves appeared to play an important role in the mechanism.