Shoot Wet Weight Research Articles

A lack of heterosis in natural poplar hybrids from southern Alberta

Shoot cuttings were collected from 56 native poplars along 11 rivers and creeks in southwestern Alberta, a region where Populus angustifolia, Populus balsamifera (sspp. balsamifera and trichocarpa), and Populus deltoïdes form a disectional, trispecific hybrid swarm. Cuttings were rooted and established in an irrigated nursery plot. After 3 years, stem diameters and heights were measured from 381 trees and whole shoots were harvested from 74 trees to establish a regression equation relating basal diameter and shoot wet weight. Shoot wet weight varied by more than an order of magnitude across the clones, and P. angustifolia clones tended to grow more slowly than clones of the other two species. There was no significant correlation between shoot growth rate and the degree of hybridization, as determined by a prior multivariate analysis of leaf form that has been substantiated by chemotaxonomic data. Thus, the interspecific hybrids were not generally more vigorous than clones with leaf forms typical of the parental species P. deltoides or P. balsamifera. Conversely, in the same environment, artificial hybrids of P. deltoides from Illinois and P. balsamifera (ssp. trichocarpa) from Washington expressed heterosis. It is theorized that introgressive genetic exchange accompanying the natural interbreeding of these three poplar species in southern Alberta minimizes their genetic distance, preventing heterosis. Key words: heterosis, hybridization, poplars, Populus, biomass.

Physiological variation between tree-associated populations of Suillus granulatus as determined by in vitro mycorrhizal synthesis experiments

Mycorrhizal synthesis studies revealed that allopatric populations of Suillus granulatus differ in host specificity. Isolates of Suillus granulatus originated from Nepal (associated with Pinus wallichiana), Korea (Pinus densiflora), and the U.S.A. (Pinus strobus). Functional compatibility of the mycorrhizal association was used to measure host specificity. Useful characters for measuring mycorrhizal compatibility were defined as those which revealed statistical differences between the uninoculated controls and mycorrhizal treatments and which were stable within one population. Useful characters, as defined by these two tests, were shoot wet weight, total wet weight, percentage mycorrhizal short roots, shoot dry weight, total dry weight, and Hartig net penetration. Data for these characters were subsequently used in anova tests to determine whether allopatric populations of Suillus granulatus differ in functional compatibility. Isolates associated with Pinus strobus were most compatible with Pinus strobus and least compatible with the other trees, whereas isolates from Pinus wallichiana and Pinus densiflora showed variable compatibility with all three trees. Phenetic analyses used to determine how similarly the isolates responded with the hosts confirmed these results. We conclude that isolates associated with Pinus strobus are most specific for this host, whereas isolates from the other two trees are not host specific. The implications of these results are discussed in light of future investigations regarding the relatedness of these tree-associated isolates. Key words: Boletaceae, Suillus, Pinus, ectomycorrhizae.