Rubber Tree Anthracnose Disease Resistance Mechanisms

The resistance of Hevea brasilliensis vary in their susceptibility to Colletotrichzon gloeosporioides. But the mechanism of defence is not fully understood. This investigation was undertaken to study the characteristics of the morphology of the leaf surface and anatomical structure, as well as biochemical properties of resistant and susceptible clones. The result showed that the density of stoma, the anatomical structure, the opening size of stoma ,the thickness of cuticle and wax lattices have close relationship with resistance to Colletotrzchwn gloeosporioides. The leaf surface of resistant clone Daling6l-l is covered with low density of stoma, where deposited with thick wax lattices .With small opening size,the stoma of resistant clone Daling6 I -1 deposited with thick cuticular ridge. The semithin sections were carried to found the difference of the cuticula thickness between moderate susceptible clone LCB87O and susceptible clone RRIC 110. It was found that the cuticula of resistant clone is thicker than that of susceptible clone RRIC 110. However the leaflet of susceptible clone PB 5/51 covered with high density of stoma ,with large stoma opening size and thin wax lattices.When fungus attacked young leaflet ,hypersensitive response. was observed on the leaf surface of resistant clone and moderate susceptible clone, however the susceptible clone did not appear hypersensitive response.The change in activity of defense enzyme (POD,PAL,SOD)after inoculation with Colletotrichum gloeosporioides was studied? The activity of POD,PAL of resistant clone (Nanqiangl-97 DaIing髄-l)increased rapidly ,not only they reach the peak earlier, but also the peak of enzymes is higher than that of susceptible clone Nanhual ,PB86,PB5/5 1. The activity of SOD of resistant clone remained stable after inoculation. However the activity of SOD of susceptible clone decreased greatly to a faint point , which lead the high concentration of activated oxygen to hurt the plant cell membrane system . The activity of peroxidase isozyme enhanced greatly and a new strong band was appeared after inoculation. However the activity of POD isozyme of susceptible clones is weaker than that of resistant clones and no new band was found. Band (PA2)of PPO isozyme of resistant clone increased a lot ,however the susceptible clone without the band PA2 still. The experiment results provide a direct evidence for the enxymes(POD,PAL,SOD,POD isozyme,PPO isozyme )activities are closely related to the disease resistance of Hevea brasilliensis . There was no marked change after inoculation in activity of esterase isozymes(EST), this suggested that EST has no significant relationship with disease resistance.The genomic DNAs isolated from 11 resistant clones and 11 susceptible clones of Hevea brasilliensis were amplified with 100 random primers by RAPD technique. a 600bp band was consistently amplified by using genomic DNAs from resistant clones as templates. However, such band was not amplified from the susceptible clones. These results suggested that the band is closely linked with the resistant gene of rubber tree to colletotrichum gloeosparioides.