Association between enzyme activity levels in Eucalyptus clones and their susceptibility to the gall wasp, Leptocybe invasa, in South China

The activity levels of five defensive enzymes, namely, peroxidase (POD), polyphenol oxidase (PPO), superoxide dismutase (SOD), phenylalanine ammonia-lyase (PAL) and catalase (CAT) were assessed in shoots of four commercial Eucalyptus clones (DH201-2, DH32-29, U6, GL9) at ages of 13, 29 and 38 months. Levels were also assessed in healthy and damaged shoots of clone DH201-2 at 15 months, shortly after it was severely attacked by the shoot gall wasp Leptocybe invasa. Foliar levels of these five enzymes did not show any significant increase with age. The level of CAT was found to be significantly higher at ages 29 and 38 months in clone GL9, a clone relatively resistant to L. invasa, than in the three other clones. Clone DH201-2, which was relatively susceptible to L. invasa, had non-significantly lower CAT levels than the rest of the clones at all three ages examined. The levels of the other four enzymes showed no obvious differences between clones and overall activity levels of the five enzymes did not show any clear association with the qualitative ranking susceptibility of the clones to L. invasa. In 15-month-old DH201-2 trees, marked increases in the levels of CAT, SOD and PPO were observed in shoots attacked by L. invasa compared with shoots from healthy trees of the same age, while levels of PAL and POD decreased compared with those in shoots from healthy trees.