Physiologic Differences between Resistant and Susceptible Cultivars Infected by Welsh Onion Alternaria Leaf Spot

In order to study resistance of welsh onion to alternaria leaf spot,evaluation of resistance of welsh onion seedling was done.Also,two varieties with different resistance to welsh onion alternaria leaf spot were used to study changes of chlorophyll content,carotenoid content,POD activity,MDA content,proline content,soluble protein content,soluble sugar content and free amino acid content.The results showed that the chlorophyll content and carotenoid content dropped on both varieties.But the susceptible cultivar dropped more than the resistant one.The POD activity of the resistant cultivar was higher than the susceptible one,and increased more than the latter.The MDA contents between two cultivars were little difference before infection.The susceptible cultivar increased more than the resistant one after infection.The proline content of the resistant cultivar was higher than the susceptible one,and increased more than the latter after infection.The soluble protein contents between two cultivars were little difference before infection.The susceptible cultivar increased a little,and the resistant one dropped after infection.The soluble sugar content of both cultivars dropped after infection,but the susceptible cultivar dropped more than the resistant one.The free amino acid content of the resistant cultivar was higher than the susceptible one,and the susceptible cultivar increased a little,and the resistant one decreased after infection.