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Increased infestation of Asian citrus psyllids on cold treated sour orange seedlings: Its possible relation to biochemical changes in leaves

Malik, Nasir S.A., Perez, Jose L., Patt, Joseph E., Zibilske, Larry M., Mangan, Robert L.
Journal of food, agriculture & environment 2012 v.10 no.2 pp. 424
Candidatus Liberibacter, Citrus aurantium, Diaphorina citri, Psyllidae, adverse effects, amino nitrogen, ammonia, bacteria, boring insects, buds, caffeic acid, cages, carbohydrates, chlorogenic acid, cold, cold stress, environmental factors, feeds, free amino acids, greening disease, herbivores, insect attractants, leaves, nutrient availability, nymphs, oviposition sites, phloem, plant response, plant-insect relations, polyphenols, putrescine, rutin, sap, secondary metabolites, seedlings, senescence, spermidine, spermine, temperature, vector control
Cold stressed sour orange (Citrus aurantium L.) seedling attracted significantly more Asian citrus psyllid (ACP) (Diaphorina citri Kuwayama) during 5 and 24 h recovery periods compared to control plants in choice test experiment. Cold stressed plants were held placed at 6±1°C for 6 days and then transferred to a cage at room temperature (28±2°C) for the ACP choice test. During these 5 and 24 h recovery periods, levels of free alpha amino nitrogen increased by 27% in 24 h post treated samples. Levels of ammonia, a known insect attractant, also increased throughout the recovery period, and after the 24 h ammonia emission was 170% higher in the cold stressed plants than in the controls. Higher levels of putrescine and spermidine were found during 24 h recovery period in cold treated plants than controls. On the other hand, spermine levels in the cold treated leaves decreased by 25% in the first 5 h but then increased to the same levels as the controls in 24 h post cold treatment samples. A number of polyphenols known to be insect deterrents decreased in cold stressed plants. For example, chlorogenic acid, rutin, homoorientin, caffeic acid, naranginin and eriodictoyl decreased significantly in the cold treated plants during 5 and 24 h recovery period. In general, cold stress that increased ACP infestation of sour orange leaves also increased the levels of biochemical insect attractants and decreased the levels of insect deterrents. Key words: Amino nitrogen, ammonia, Asian citrus psyllid, cold stress, polyamines, polyphenols. Introduction Asian citrus psyllid (ACP), Diaphorina citri (Kuwayama), is a vector for the bacteria (Candidatus Liberibacter spp.) known to cause the devastating Huanglongbing (HLB) or the citrus greening disease 9, 18. ACP feeds on phloem saps; young newly emerging bud growth is the primary site for ACP oviposition and nymph colonization 18. There is no known cure for HLB, so the primary efforts to manage the problem are through the control of the vector psyllids 18, 39, 40. Several biotic and abiotic stresses or stimuli affect the interaction of insects with host plants 2, 19, 48. Stress in general initiates senescence and senescence is known to promote proteolysis that enhances levels of free amino acids in tissue providing attractive feeding opportunities for herbivore insects 25, 35, 46, 49. However, not all insects respond similarly to stress induced nutrient availability. For example, while stress might have positive effect for boring and sucking insects it had adverse effect on gall-makers and chewing insects 24. Changes in secondary metabolites (e.g. polyphenols) which generally act as a deterrent to insects also occur in plant tissue under stressful conditions 45. Generally, increased levels of polyphenols in the leaves have been reported to increase defense response or resistance in several plants 13, 15, 23, 34. Changes in polyphenols could occur from changes in the environmental conditions or by the feeding of herbivores 11, 44. Polyphenols in free form, or in some cases as esters of carbohydrates (e.g. caffeic acid esters), could promote resistance response in plants due to their deleterious