The Asian citrus psyllid (ACP) (Diaphorina citri) avoids colonizing trifoliate orange (Poncirus trifoliata). The proximity of Poncirus leaves, especially mature leaves, to citrus hosts regularly colonized by ACP produces a significant reduction in the number of eggs laid by ACP. Compositional analysis of mature versus immature leaves of Poncirus trees showed remarkably contrasting profiles. Of particular note are compounds tentatively identified as eriodictyol-di-C-glucoside and hesperetin-di-C-glucoside in the leaves of young leaves, but which were undetected in mature leaves. During leaf transition from immature to mature, there were similar drops in concentrations of a number of flavanone glycosides, and the main flavone-C-glycoside (fortunellin). In contrast, most of the flavone-O-glycosides showed no such decreases during the maturation of the Poncirus leaves. Nine linear furanocoumarins were detected in Poncirus leaves, including two unknown compounds and seven identified compounds: xanthotoxin, bergapten, isopimpinellin, prangenin, imparatorin, phellopterin and cnidicin. These compounds occurred at nearly the same concentrations in the mature leaves and young flushes, with the exception of xanthotoxin which was sharply lower in concentration in the mature leaves. Interactions between insects and plant furanocoumarins have been extensively investigated, and trace levels of furanocoumarins in Poncirus leaves may occur near the leaf surfaces and play as of yet unknown roles as a behavior modifying agent for the ACP.

Seasonal changes in trifoliate orange (Poncirus trifoliata) leaf polyphenols

2019 Spring National Meeting

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