Dao Ngoc Quang, Le Van Binh
Forest Science Institute of Vietnam
Dendrolimus punctatus Walker is the most damaging pest to Pinus merkusii Jungh. &Vriese in terms of both level of attack per individual tree and percentage of trees attacked in a location. It causes not only serious losses in yield as well as wood and resin quality, but also effects the ecological environment. However, about three hectares of 30 year old P. merkusii plantation in Son Loc commune, Can Loc district, Ha Tinh province have not been attacked by D. punctatus, while an adjacent large plantation are of the same age is heavily attacked by D. punctatus annually.
In order to determine the basis of pest and disease resistant tree breeding, we carried out research on that P. merkusii plantation to find out the resistance mechanism to D. punctatus:
· Surveying to discover individual resistant trees.
· Biochemical analysis of leaf samples of resistant and susceptible trees.
· Rearing larvae in laboratory.
· Rearing adults in laboratory.
· Comparison of some characteristics between resistant and susceptible tree.Study results show that there are two initial determining mechanisms in Pinus merkusii to Dendrolimus punctatus:
· Antixenosis
o Differences in morphological characteristics and construct of leaf sample of resistant and susceptible tree: cutin layer and epidermal layer of leaves of the resistant tree are deeper than leaves of the susceptible tree; hypodermis and parenchyma is thinner so D. punctatus larvae don’t like them.
o Differences in some other characteristics between resistant and susceptible tree such as branch angle distribution, resin color and production.
o When conducting larvae rearing experiments in the laboratory, the adults do not lay eggs on the resistant trees; and the larvae moved to susceptible trees after only a short time (several hours after hatching) to find suitable food. Such can be said that the chemical composition in leaves of resistant and susceptible trees has a different volatile which can affect both adults and larvae.
· Antibiosis
o There are clear differences in oil composition in leaf sample of resistant and susceptible trees. Some substances that appear only in the leaves of susceptible trees did not appear in the leaves of resistant trees.o Content of component of group Terpenes in the leaves of the resistant trees is higher than leaves of susceptible trees.However, to determine the mechanism of resistance in Pinus merkusii to Dendrolimus punctatus needs further research.
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