Studies On Effective Control Of Citrus Canker Disease

In order to control the spread of citrus canker, which is a worldwide disease, and to minimize the growers’losses, pathogenesis of the disease should be investigated. A Vantage Pro2type automatic meteorological observatory was installed in the orchard to monitor meteorological factors, and the growth of shoots and fruit was recorded. At the same time, screening of chemicals and active agents was carried out.Breeding resistant varieties is an effective way to solve the disease problem. Citron has hypersensitive reaction and shows active resistance to citrus canker. It was used as male parent to hybridize with female parents like Shatian pomelo, Hongxin pomelo, Jinlan pomelo and Bingtang sweet orange. Up to now,43F1hybrids were obtained and36of them were assayed for their behavior to canker disease.The results are as follows:The first canker disease spot appeared on spring, summer and autumn shoots when young leaves almost reached the full size and the young fruits after the first physiological fruit drop.A prediction equation was formed:△Y=48.059+0.905X1-0.513X6-0.196X7, R△Y=0.959*, by disease index variation (△Y) and the number of rainy days (X1), average humidity (X6) and the days after shoots shearing (X7).In the screening of chemicals and active agents, new copper chemicals are considered to be the best ones."Spartan" active agents for copper chemicals can play better synergies, the control efficiency on partial new shoots reached a significant difference compared with copper chemical.In the resistance assay by inoculation with citrus canker pathogen,36F1hybrids resulted in a wide range of separation after. Resistant hybrids were:E41, E26, E43, E80, Y8, Y11; and the susceptible ones were:E55, E72, E48, E59, E19, E73, E13,2B9, B174, B64, Y23, Y22, Y18, Y9, E29, E64, E74. The ratio between the susceptible hybrids and the resistant ones is5:1.