| The eucalyptus forest is the main forest resource in south China. It is one of the widely planted and fast-growing timer species. There are tens of thousands of hectares of artificial eucalyptus foresty which are developing by leaps and bounds in Fujian province. However, because of the cultivation of large area of man-made pure eucalyptus forest and inadequate management, the eucalyptus growing environment becomes worse and worse, the varieties of eucalyptus disease increase, develop frequently and occur wider and wider. The eucalyptus dieback which caused 12．5 hm of eucalyptis to wither and die was found for the first time in the forest-experimental station of Tuanshi in Yong'an County in Fujian province in July 1999, and for this reason, the civil forestry department released the epidemic situation to notify. Nowadays, the control measure of eucalyptus dieback in China is mainly base on chemical control. Although chemical control has acquired great effect, it is also difficult to control the disease economically, effectively and persistently now. Fujian has formed rich resource of cultivatation varieties (strains) in the long process of introduction and cultivation, it will be a available and possible way to utilize and enhance the resistance of the host for controlling eucalyptus dieback.In order to provide the evidences for selecting excellent and resistant varieties (strains), controlling the disease effectively and clearing away the obstacles for wide and all-round development of eucalyptus cultivation, We made scientific researches on the investigation, collection and identification of eucalyptus varieties (strains) that are widely planted in Fujian province, measured varieties (strains) resistance by artificial inoculation and natural infection, and were engaged in the physiological and biochemical changes of each variety (strain) after inoculated with Cylindrodadium quinqueseptatum. The results are as follow:1．We investigated, collected and identified eleven kinds of eucalyptus variety (strain) in Yong'an County, the serious region of eucalyptus dieback in Fujian, and established experimental site. According to artificial inoculation and natural infection, we divided the eucalyptus varieties (strains) into resistant varieties (strains) (E. grandisxE .urophylla 9224, E. grandisxExamaldu-lensis M1) , middle resistant varieties (strains) (E.grandisxE.camaldulensis 201-2, Eucalytus dunnii Maiden, Eucalyptus Saligna, E. grandisxE.urophylla guang9, E.urophyllaxE.grandis Ug9) , middle susceptible varieties (strains) (Eucalyptus bethamii, E.urophylla xE.grandis 3229) and susceptible varieties (strains) (Eucalyptus grandis 3, Eucalyptus grandis 5) .2．The contents of polyphenols in healthy leaf or disease foliage of resistant varieties (strains) were higher than that of susceptible varieties (strains). The contents of polyphenols of resistant varieties (strains) and susceptible varieties (strains) all promoted after inoculation, and with the increasement of infection index, the promotion percentage decreased. The contents of flavonoids in healthy leaf or disease foliage were resistant varieties (strains)>middle resistant varieties (strains) > middle susceptible varieties (strains) > susceptible varieties (strains), which changed regularly, and the promotion percentage of flavonoids in disease foliage of each eucalyptus variety (strain) did not change regularly. So the contents of polyphenols and flavonoids in leaves can be used as the criterions to estimate the host resistance in the measurements of eucalyptus resistance to eucalyptus dieback.3．The peroxidase (POD) activities showed no differences with the increasement of infection index among different varieties (strains) in healthy leaves before inoculation. The peroxidase activities in resistant varieties (strains) and middle resistant varieties (strains) remained higher than those of middle susceptible varieties (strains) and susceptible varieties (strains) from Oh to 60h. Variance analysis showed that peroxidase activity in each variety (strain) was significantly different. The changes of perocidase special activities were similar to those of peroxidase activities after inoculation, which showed that not only peroxidase prossessed by the sick plant was activated, but also added some new peroxidase enzyme. The level of peroxidase activity can be used as the biochemical criterion to estimate the host resistance. However, the peroxidase isozyme showed no differences among each variety (strain) in healthy and sick organ, so peroxidase isozyme can not be use as the criterion to estimate the host resistance.4．No matter in healthy or sick organ, the polyphenoloxidase (PPO) activities of resistant varieties (strains) were higher than those of susceptible varieties (strains), and the polyphenoloxidase activities in different varieties (strains) were significantly different. With the increasement of infection index, the polyphenoloxidase activity of healthy organ decreased before inoculation, and the higher the polyphenoloxidase activity and polyphenoloxidase special activity were, the stronger variety (strain) resistance. The polyphenoloxidase activity of each variety (strain) increased after inoculation, activity had regularly relative to the resistance to the disease, the changes of polyphenoloxidase special activities were similar to those of polyphenoloxidase activities.Therefore, the level of polyphenoloxidase activity can be use as the criterion to estimate the host resistance. The activities of polyphenoloxidase isozyme of resistant varieties (strains) and middle varieties (strains) were obviously stronger than those of middle susceptible varieties (strains) and susceptible varieties (strains) before and after inoculation. After inoculation, the resistant varieties (strains), appeared two new polyphenoloxidase isozyme bands, the middle resistant varieties (strains) appeared two bands except E.urophylla xE.grandis Ug9 only appeared one new band, the middle susceptible varieties (strains) appeared one new band, but susceptible resistant varieties (strains) had no change. The resistance of different varieties (strains) to the disease concerned with the number of the bands and the strength of polyphenoloxidase isozyme. These provide an evidence for the measurements of host resistance to eucalptus dieback.According to the results above, E.grandisxE.urophylla 9224, being the characteristics of being fast-growing and high-yielding, growing into timber in a short time, high resistance, high percentage of getting hold of pulp, being adaptable and high economic benefit, is known as excellent tree for papermaking and wood based panel. So in order to control eucalyptus dieback, we suggest setting up E.grandisxE.urophylla 9224 nursery and producing a large number of tissueculture seedlings for popularizing in eucalyptus planation. |
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