Studies On Biochemical Marker Of Pepper Blight Resistance And A RAPD Marker Linked To Phytophthora Capsici Gene In Capsicum

Pepper blight is a very serious disease of Capsicum annum in the world. Experiments were conducted to study the main cultivars resistance to Phytophthora capsici, several biochemical components in six Capsicum cultivars with different resistance to Phytophthora capsici before and after infection, a RAPD marker linked to Phytophthora capsici resistant gene.The screening of Capsicum cultivars for resistance to Phytophthora capsici was proceeded at seedling stage in the glasshouse. Of the 30 cultivars tested,2 were highly resistant,5 resistant, 13 medium and 10 susceptible.The experiment result showed that , not only in healthy plants but in the infected, the content of soluble sugars was higher in susceptible cultivars than that in resistant ones. It implied that pepper blight was a kind of ''high sugar disease". It was very apparent that the more resistant the cultivars, the higher the content of soluble protein. The content of soluble protein reached the peak at 96th hour after inoculation.The changes of protective enzymes' activities and isoenzyme bands were studied. The results showed that the activities of POD and AsA-POD in healthy leaves were significantly higher in resistant cultivars than those in susceptible ones. The activities increased both in resistant and susceptible cultivars after inoculation. The activities were significantly higher in susceptible cultivars than those in the resistant during 96"'-120th after inoculation. The PPO activities increased both in the resistant and susceptible cultivars after inoculation, and their peaks were higher in highly resistant cultivars than those in the susceptible. However, the activities didn't increased sharply in resistant and medium resistant cultivars. The PAL activities increased greatly both in the resistant and susceptible cultivars after inoculation. At96th hour after inoculation the PAL activities reached the peaks, which were lower in the susceptible cultivars than those in the resistant.The POD isoenzyme bands were not significantly different before inoculation among the three pepper cultivars with different resistance. However, the PPO isoenzyme bands of susceptible cultivars were significantly weaker than those of the resistant before inoculation. A new band of POD and PPO isoenzyme appeared in all cultivars tested after inoculation. The new band POD and PPO isoenzyme were stronger in highly resistant and resistant cultivars than that in the susceptible.The analysis of inheritance showed that the cultivars resistance to Phytophthora capsici was controlled by one dominant gene. Randomly amplified polymorphic DNA(RAPD) was employed to detect a molecular marker linked to Phytophthora capsici resistant gene in the capsicum. A RAPD marker OPA18550 was proved to be linked to the resistant gene. This work will be helpful to molecular marker-assisted selection for disease resistance and make location and cloning of disease resistant genes possible.