QTL Mapping For Leaf Area, Growth, Phenolic Compounds And Borer Resistance In Populus Deltoides

Poplar is one of main forest tree species for afforestation and industrial timber in China, and its planting area amounts to 6.67 million hm2. However, a heavy loss of poplar plantations have been brought about due to the impacts of poplar borers, among which Anoplophora glabripennis and Anoplophora nobilis Ganglbauer are two main species. The 'Shanbei'forest-defending belts system has been seriously damaged. Therefore, it is critical to protect poplar plantations from borer damage and to breed new poplar varieties of resistance to insects. QTL (Quantitative traits loci) mapping for borer resistance is of both theoretical and practical significances to map-based cloning, genetic basis for insect resistance and marker assisted selection. On the basis of a P. deltoids backcross population, an integrated AFLP (Amplified fragment length polymorphism) linkage map is constructed by applying two-way pseudo-testcross method. Morphologic polymorphism of tissue-culture seedlings and rooting traits are investigated. According to the survey of phenotypic traits of the leaf, growth, phenolic compounds and borer-resistance in the backcross population, QTLs for variation of these traits are analyzed, and the main results are as follows. A segregated backcross population from the cross between F1 clone P. deltoides Cl. 'Nankang1'with high resistance to Batocera horsfiedi (Hope) as female and its father P. deltoides Bartr. Cl. 'Harvard'(I-63/51), is successfully generated by the artificial control pollination. Based on the progeny test plantations of the backcross, resistances to Anoplophora glabripennis and Apriona germari (Hope) are tested. The progeny test plantations can be used as breeding populations for selection of new varieties with the properties of fast growing and resistance to borers. Polymorphism in morphologic and rooting characters in the backcross progeny tissue-culture seedlings is investigated. It is firstly reported that P. deltoides seed rooting character is a qualitative trait, and controlled by a single gene with a pair of alleles and a complete dominance of one allele over the other. By the method of water cultivation with junior twigs, there is not a significant difference in growth of the selected clones between high and low content nutrition solutions, and a significant difference between selected clones is not observed as well in terms of the total dry root weight. However, a significant difference between clones exists in terms of the total weight of the second-class. In the water cultivation with the low nutrient content solution, there is a significant difference between clones in the number of the first class root and their length. Analyses show that the leaf area is significantly related to the leaf length and the leaf width (α=0.01), but the leaf length is not significantly related to the leaf width. The ratio of the leaf length to width is positively related to the leaf length, and negatively related to the leaf width at a significant level (α=0.01). And the leaf area is also positively related to the height and the base diameter of the seedlings at a significant level (α=0.01). Under the mechanism wounding, the contents of several phenolic glycosides, present in either constitutive or inducing status, and their total content, can be increased to different levels(15.1%?59.8%). The increase in salicortin content is substantial, about 59.8%. The contents of phenolic glycosides are genetically controlled by more than one gene. The study on the relationship between the phenolic glycosides and the beetle attacks is original. There is a significantly positive correlation between the deltoidin content and the resistant ratio to Apriona germari (Hope) (α=0.01), and a significantly negative correlation between the total content of phenolic glycosides and the larva density of Anoplophora glabripennis (α=0.05), indicating that the effects of phenolic glycosides to borer attack comes from different types of phenolic glycosides and their contents. Apriona germari (Hope) is sensitive to deltoidin, while Anoplophora glabripennis is affected by the total content of phenolic glycosides.