Screening Of Indexes For Evaluating Paulownia Wood Color And Selection Of Paulownia Individuals With Excellent Wood Color

Paulownia tree is one of the most important timber uses species. The Paulownia wood isof great quality. However, wood stain occurs after sawing, which seriously affects theappearance and visual characteristics, and thus reduces the economic value. Therefore, it isnecessary to improve the Paulownia wood color by soaking and bleaching before processingand marketing. This can increase extra cost and even pollute the environment, while the stainfrequently reappears after a period of time. Soaking and bleaching can not fundamentallyeliminate wood discoloration. At present, breeding of Paulownia focuses on fast-growing,stem form, disease resistance, ect., while the wood color characters which can greatly affecteconomic values have not been considered as breeding objectives. The wood color ofPaulownia was improved by selective breeding in this study, because the traditional methodcan not completely eliminate the wood stain of Paulownia. Variation pattern of wood colorwas analyzed, Paulownia individuals with excellent wood color, fast-growing, stem form, andwithout disease were selected, taking Paulownia resources all over the country as population,meanwhile, a series of physiological indexes were measured, correlation between thephysiological indexes and wood color indexes of these samples was analyzed to provide basisfor indirect selection of wood color. The main results are as follows:1. Hunter whiteness is most applicable for evaluating Paulownia wood color from allcolor indexes.The lightness index value on Paulownia samples wood color ranged from70.58to85.166, the red degree ranged from-5.59to7.102, yellowing degree ranged from12.128to23.618. The tristimulus values of Paulownia wood color changed synchronously, whichslightly changed the red degree and yellow degree. The correlation between Hunter whiteness,color chromatism and lightness of Paulownia wood color was extremely significant. Therefore, the color quality could be evaluated by Hunter whiteness, color chromatism and lightness. Thecorrelation between L*a*b*color space and the characteristics of the human visual was moreclose than XYZ color space, therefore, Hunter whiteness was more applicable than Ganzwhiteness for evaluating Paulownia wood color.2. Rich variation on wood color existed among different Paulownia species, provenancesand individuals, Hunter whiteness of Paulownia fortunei is the highest from all Paulowniaspecies.Difference of Hunter whiteness, color chromatism and lightness among Paulowniaspecies and was statistically significant, while the difference of red degree and yellow degreewas not significant. Difference of Hunter whiteness, color chromatism, lightness, red degreeyellow degree among Paulownia fortunei provenances were significant, the top sixprovenances by Hunter whiteness were hunan chenzhou, jiangxi fuzhou, fujian nanping,jiangxi jiujiang, fujian longyan and guangxi guilin. Wood color of Paulownia fortunei variatedwith its natural distributions, which in the western area were of low quality, those in theeastern area were of high quality. Difference of each color index among individuals inprovenance was extremely significant, the variation of color indexes except for red degreefrom individuals was larger than that from provenances. Therefore, selection of Paulowniafortunei should be carried on directly by individuals.3. Phenol content was the most applicable for indirect selection of Paulownia wood color.Absorbance of extract of three-years-old branch xylem by90%methanol after being placedfor one year can also be used for color indirect selection, while oxidase activity, kinds ofisozyme, paulownin and sesamin content can not be used for the reference of indirectselection.Phenol and sugar content in three-year-old branch xylem negatively correlated with woodHunter whiteness, phenol content in the annual branch xylem after grafting propagation also negatively correlated with wood Hunter whiteness, but sugar content positively correlated withHunter whiteness, which disagreed with the traditional theory. The activity of polyphenoloxidase in leaves at fast-growing stage and slow growth stage positively correlated withHunter whiteness, which disagreed with the traditional theory, the activity of peroxidases inleaves of slow growth stage negatively correlated with Hunter whiteness, while the activityand specific activity of peroxidases in leaves at fast-growing stage did not correlate withHunter whiteness; individuals which had similar Hunter whiteness did not prior clustertogether according to the result of clustering analysis of isozyme patterns; activity ofpolyphenol oxidase and peroxidases in phloem and xylem did not correlate with wood colorindexes, the enzyme activity and the decline extent of activity after being placed at roomtemperature for3months also did not correlate with wood color indexes. Content ofpaulownin and sesamin in three-year-old branch xylem negatively correlated with red degree,but they did not correlate with Hunter whiteness.4. According to the breeding objective, six individuals which are excellent on wood color,fast-growing, stem form, and without disease were selected from96Paulownia fortuneiindividuals: fortunei9-1, superior fortunei4, superior fortunei3, superior fortunei5, superiorfortunei25and fortunei12-2.The selection rate was6.25%, the average Hunter whiteness values of individualsselected reached75.694, selection differential was4.228, selection intensity was1.605. Theseindividuals could be used for cultivating clones, and laying a foundation for the breeding ofexcellent varieties.