Abstract
The woolly apple aphid,Eriosoma lanigerum Hausmann,is native to eastern North America.It threatens the survival of apple trees by infesting shoots and roots,ultimately resulting in decreased apple production.The woolly apple aphid has spread to most apple-growing regions of the world and is now an important pest in apple production areas.The following control methods have been tested: chemical control,biological control,agrotechnical control and host plant resistance.However,chemical control causes resistance,residue and resurgence(the 3R problem),biological control is constrained by climate,and agrotechnical control wastes time and resources.Consequently,host plant resistance seems optimal because it is safe,effective and economically viable.Some studies have shown that physiological indices can indicate the insect resistance of a plant.To reveal the relationship between physiological indices in apples and resistance to woolly apple aphid,we studied changes in soluble sugar,protein,free amino acids,total phenolic compounds and defense enzymatic activities in five apple cultivars damaged by E.lanigerum.The five apple cultivars studied were Red Fuji,Golden Delicious,Zhaojin 108,Qinguan and Red General.Red Fuji is the most sensitive cultivar and Qinguan the most resistant.Golden Delicious,Zhaojin 108 and Red General demonstrate average resistance.To examine physiological indices,one-year-old injured branches from the lower parts of the trees were clipped and frozen with Drikold.Undamaged branches were treated using the same method as for the control group.Results showed that the soluble sugar contents increased in damaged branches,except in those of Red General trees.Soluble sugar contents in Red Fuji increased by 13.7%.Protein contents in the four cultivars besides Red Fuji decreased.Amino acid contents increased in all five cultivars,increasing by 68.8% in Red General.Total phenolic compound is an important defensive substance against aphids.The total phenolic compound was increased in Red Fuji,Zhaojin 108 and Qinguan after damage by woolly apple aphid,and the rate of change of total phenolic compound in Zhaojin 108 and Qinguan was about twice that of Red Fuji.The Superoxide Dismutase(SOD),Peroxidase(POD),Polyphenol Oxidase(PPO) and Catalase(CAT) activities in Red Fuji were markedly lower than that in Zhaojin 108.The SOD activity was increased in all five cultivars.Activities of PPO and POD were increased in all cultivars except Red General.The activity of CAT in Golden Delicious and Fuji increased by 110.8% and 45.5%,respectively.Plant resistance to pests is closely linked with the defensive enzymes exhibited by the plant.It is suggested that the contents of soluble sugar,amino acids and the activities of SOD,POD,PPO and CAT affect host selection by woolly apple aphids.Changes in physiological indices in different apple cultivars are associated with resistance to woolly apple aphid.
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