Variation of stem growth and morphology traits of exotic pine hybrids and their correlations.
The hybrids studied include Pinus elliottii Engelman var. elliottii (PEE) × P. caribaea var. hondurensis (PCH), PEE × P. caribaea var. caribaea (PCC), PEE × P. caribaea var. Bahamensis (PCB), P. taeda L. (PTA) × PCH, PTA × PCC and PTA × PCB and they were tested by randomized complete block design with 5 replicates, single tree row plot in field located in the hilly area of mid-north subtropical zone. The tree stem height (H), Diameter at breast height (DBH), stem straightness (SF), branch size (BZ), branch layer number (BLN) and branch angle (BA) of the pine crosses at the age of five years were measured. At the same time, needle length (NL) and needle sheath length (FSL) of the hybrids and their parents were measured. The results of variances analysis showed that the stem growth and morphology traits of six pine hybrids have abundant diversity among different pine taxon, families and individuals. The coefficient of variance for stem volume and straightness was 30%-50%, and 2%-30% for other growth and morphology traits. Some of the variances had potential uses in selection of pine varieties with high yield and tolerance to the bad weather. For example, the needle length of the crosses of PEE and caribaea pine was shorter than their parents, and PEE × PCH had better stem form with good straightness and small branch angles. The crosses of PTA × PCH had several good growth and morphology traits such as fast growth, thin branches, small branch angle and good stem form. The correlation showed that the traits of stem growth, needle length, branch angle and stem straightness can be improved easily because they had positive correlation. Totally the research revealed that the exotic pine hybrids such as PEE × PCH had varieties with good stem growth and more tolerance to heavy snow and sleet storms, which was very important for the tree breeding under the climatic change circumstances all over the earth.