Physiological And Biochemical Responses To Bemisia Tabaci Feeding And Induced Volatile Changes By Cucurbit Chlorotic Yellows Virus In Cucumber

B(Middle East-Asia Minor 1)and Q(Mediterranean)biotypes,two cryptic species of Bemisia tabaci species complex,are important agricultural pests in China and worldwide.Extensive applications of insecticides for control of the pests have resulted in pesticide resistance in whiteflies,have endangered ecological safety and human health.Implementation of safe pest management strategy is therefore becoming very important and urgent.Utilization of plant defense is one of the important components in pest management control.The objective of this research was to investigate the differential responses of nutrients and defensive enzymes in cucumber induced by the feeding of Bemisia tabaci B and Q biotypes and thereby to elucidate the physiological and biochemical mechanism underlying defence responses of cucumber to B.tabaci.At the same time,CCYV-induced volatile were detected to analyze plant responses of volatile secondary substances to virus infestation.The experiments were conducted in the chemical ecology laboratory of Henan Agricultural University,China.Adults of Bemisia tabaci B and Q biotypes and cucumber plants(var.Bojie-I)from the laboratory cultures were used for the experiments.The cucumber plants at four leaf stage were respectively used to feed 200 adults of B.tabaci B and Q biotypes,with healthy plants as controls,and the contents of nutrients(soluble sugar and soluble protein)and polyphenolic contents,activity of phenylalanine ammonia-lyase(PAL),the enzyme of defensive substance biosynthesis,activity of protective enzymes in cucumber were determined after continuously feeding 1,3,5,7 and 9 days by B and Q biotypes of B.tabaci.At the same time,cucumber plant(var.Bojie-I)and Cucurbit chlorotic yellows virus variety were used to study the volatile released by health and infected cucumber.The volatiles were collected using the method of dynamic headspace collection and analyzed using GC-MS.The main results are as follows:1.The experiment of differential physiological and biochemical responses in cucumber to the feeding by Bemisia tabaci B and Q biotypes indicated that the contents of soluble sugar and protein in cucumber increased after 3-d infestation or later by B.tabaci B biotype,but decreased after 1-d feeding or later by B.tabaci Q biotype,compared to those in controls.The contents of polyphenols and activity of phenylalanine ammonia-lyase(PAL),the key enzyme in its biosynthesis pathway,increased after infested both by B and Q biotypes,with higher activities to Q biotype feeding.Activity of superoxide dismutase(SOD)and catalase(CAT)increased and the activity of peroxidase(POD)decreased after feeding by B biotype,while the activity of SOD increased and the activity of POD and CAT decreased after feeding by Q biotype.Differential changes of nutrients and defensive enzymes in cucumber after the feeding of Bemisia tabaci B and Q biotypes were found in the present study.both B and Q biotypes of B.tabaci were able to induce the synthesis of defense substance polyphenols,and increased the content of polyphenols in cucumber;but there were differences in inducing the contents of nutrients and the activities of protective enzymes,i.e.,more nutrients in cucumber by B biotype feeding,while higher activities of defensive enzymes by Q biotype feeding.2.The analysis of health and infected cucumber indicated that the healthy cucumber plants contain specific volatile,such as linalool,but CCYV-infected cucumber plants contain 1-Hexacosene,butyl acetate and cholesterol.The infection by CCYV induced that the content of d-Camphora reduced by 47.25% to 28.17%.Terpenes,functioning in the interaction of plant-whitefly-predators,can attract or repel whiteflies.Ecological or behavioral effects of induced volatiles in plants by CCYV on whitefly remain to be further studied.