Defensive Response Of Cotton Induced By Tetranychus Cinnabarinus Feeding And Its Effect On The Development Of Aphis Gossypii

Inducible defenses is an important strategy of plant against herbivores invasion. Tetranychus cinnabarinus and Aphis gossypii are both serious pests of cotton seedling in North China. In this study,induced defence response of cotton to the feeding of T. cinnabarinus and its effect on the development of Agossypii were determined. This research revealed that the T. cinnabarinus feeding induced defensive response in cotton is density dependent, and these induced defences showed negative effect on cotton aphid and played important roles in plant-mediated interspecific interaction between T.cinnabarinus and A.gossypii.The defensive enzymes (PAL, LOX, PPO and POD) activities and the secondary metabolites(gossypol and condensed tannins) contents were enhanced remarkably in cotton seedling leaves infested by T. cinnabarinus at density of 10 and 15 ind/cm2 at 24, 48 and 72 hr post infestation. The most defense enzymes activities and the secondary metabolites contents were significantly higher than control in cotton leaves infested by T. cinnabarinus at 5 and 8 ind/cm2 at 48 and 72 hr post infestation.The T. cinnabarinus-induced production of defense enzymes and secondary metabolites was correlated with infestation density.The contents of salicylic acid was enhanced remarkbly in cotton seedling leaves infested by four density (5 ind/cm2, 8 ind/cm2, 10 ind/cm2 and 15 ind/cm2) T. cinnabarinus at 24, 48 and 72 hr post infestation.The contents of salicylic acid in cotton seedling leaves infested by four density T.cinnabarinus was 1.22, 1.48, 1.78 and 2.19 times that of control, respectively, at 24 hr post infestation.Which was 1.43, 1.57, 2.01 and 2.62 times that of control, respectively,at 48 hr post infestation and was 1.80, 1.81, 1.75 and 1.96 times that of control, respectively,at 72 hr post infestation.The expression of genes (PAL,NPR1 and EDS1) of cotton seedling leaves infested by there density(5ind/cm2, 10ind/cm2,15ind/cm2) T. cinnabarinus were enhanced remarkbly at 24, 48 and 72 hr post infestation. The expression of PAL of cotton seedling leaves infested by there density T. cinnabarinus was 1.73, 2.59 and 3.78 times that of control, respectively, at 24 hr post infestation and which was 1.98,2.49 and 2.85 times that of control, respectively, at 48 hr post infestation and which was 2.50, 2.51 and 2.76 times that of control, respectively, at 72 hr post infestation. The expression of NPR1 of cotton seedling leaves infested by there density T. cinnabarinus was 2.32, 3.77 and 4.93 times that of control,respectively, at 24 hr post infestation and which was 2.68, 3.44 and 4.30 times that of control,respectively, at 48 hr post infestation and which was 3.35, 3.54 and 3.40 times that of control,respectively, at 72 hr post infestation. The expression of EDS1 of cotton seedling leaves infested by there density T. cinnabarinus was 1.15, 3.30 and 4.17 times that of control, respectively, at 24 hr post infestation and which was 1.93, 2.40 and 2.58 times that of control, respectively, at 48hr post infestation and which was 2.58, 2.45 and 2.42 times that of control, respectively, at 72 hr post infestation.The developmental duration of A.gossypii nymph was remarkably increased and the mean relative growth rate was remarkably reduced in cotton infested by the high dentisy T. cinnabarinus. The developmental duration of A. gossypii nymph was 1.16 and 1.18 times that of control, respectively, in the cotton infested by T. cinnabarinus at the density of 10 and 15ind/cm2.The mean relative growth rate of A. gossypii was 0.71 and 0.62 times that of control, respectively, in cotton leaves infested by T.cinnabarinus at density of 10 and 15ind/cm2. The fecundity of A. gossypii had no significant difference in differet density T. cinnabarinus infested cotton.The defense enzyme activities and secondary metabolites contents of cotton were enhanced remarkbly after different concentration (1.0 mmol·L-1, 2.0 mmol·L-1, 5.0 mmol·L-1 and 10.0 mmol·L-1)exogenous SA treatment (P<0.05). The activities of PAL, LOX and PPO reached a peak at 24 hr and the activities of POD reached a peak at 12 hr after different concentration exogenous SA treatment. The contents of gossypol reached a peak at 36 hr after lmmol·L-1 and 2mmol·L-1 SA treatment and at 24 hr after 5mmol·L-1 and 10mmol·L-1 SA treatment. The contents of condensed tannin increased gradually after different concentration exogenous SA treatment. The developmental duration of A. gossypii nymph fed on cotton treated with 1.0 and 2.0 mmol·L-1 SA were all 1.06 and 1.08 times that of control,respectively.The fecundities per female were 18.4% and 20.4% less than the control, respectively.This study identified the induced defense responses of cotton to different density Tetranychus cinnabarinus feeding and its effect on development of Aphis gossypii. This study provides a theoretical basis for the study of the induced defense responses of plants to different degrees of feeding stress and the role of plant induced defenses in interspecific interactions.