Submitted to: Journal of Food Agriculture and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 8, 2011
Publication Date: February 28, 2012
Citation: Malik, N.S., Perez, J.L., Patt, J.M., Zibilske, L.M., Mangan, R.L. 2012. Increased infestation of Asian citrus psyllids on cold treated sour orange seedlings: Its possible relation to biochemical changes in leaves. Journal of Food, Agriculture and Environment. 10(2):424-429. Interpretive Summary: Asian citrus psyllids (ACP) are vectors of the devastating citrus greening disease. Since there is no cure for this disease, it is crucial to find ways to manage the vector. To develop efficient management strategies for the psyllid vector, it is important to understand the physiology and biochemistry of its interactions with host plant under different environmental conditions. It has been reported in the literature that various environmental stresses could have pronounced effects on the outbreak of insect herbivores. However, little is known regarding the effect of environmental stresses on the ACP interactions with its host plants. Citrus growing areas of southern Texas encounter unique environmental conditions where heat waves could interrupt winter conditions for several days. Therefore in this study, we investigated the interaction of ACP with host plants that are brought to warm temperatures (mimicking heat waves in winter) from cold winter conditions. Results of this study indicated that plants that were cold-stressed attracted more psyllids during their recovery period (5 and 24h) under warm temperatures than the plants that were continuously grown under warm conditions. Biochemical analysis showed that the levels of free alpha amino nitrogen were increased during the cold stress recovery period. Similarly, higher levels of ammonia were observed during the recovery period of cold-treated plants compared to controls that were continuously kept under warm conditions. The levels of two polyamines significantly increased in leaves during the recovery period while the level of a third slightly decreased but returned to the level of the control plants 24h after recovery. In addition, the levels of most of the polyphenolic compounds that are known to deter insects were lesser in quantity in cold- stressed plants compared to control plants. In general, cold stress that increased ACP infestation of sour orange leaves also increased the levels of biochemicals that attract insects and decreased the levels of insect deterrent. The biochemical changes produced by cold stress in sour orange leaves appear very similar to biochemical changes noted for various plants subjected to different stresses that similarly promoted plant-herbivore interactions.
Technical Abstract: Cold-stressed sour orange seedling (Citrus aurantium L.) attracted significantly more Asian citrus psyllid (ACP) (Diaphorina citri Kuwayama) during 5h and 24h 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 5h and 24h recovery periods, levels of free alpha amino nitrogen increased by 27% in 24h post treated samples. Levels of ammonia, a known insect attractant, also increased throughout the recovery period, and after 24h ammonia emission was 170% higher in the cold-stressed plants than in the controls. Higher levels of putrescine and spermidine were found during 24h 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 5h 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 5h and 24h 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.