Morphological and Physiological Responses of Hybrid Aspen (Populus tremuloides Michx. × Populus tremula L.) Clones to Light In Vitro

Abstract

Micropropagation of fast-growing tree genotypes such as the hybrid aspen (Populus tremuloides Michx. × Populus tremula L.) is increasing. The efficiency of micropropagation depends on the luminaires, hence luminescent electric diodes (LED), which emit light of a narrow spectrum, are gaining popularity. Mostly, different LEDs are combined to increase the photosynthetic efficiency. However, light also acts as an environmental signal, which triggers specific responses in plants, which are genotype specific, and regarding hybrid aspen, are likely affected by heterosis. In this study, morphological and physiological responses of clones of hybrid aspen with contrasting field performance to the spectral composition of illumination were studied in vitro. Among the 15 variables measured, area of leaves and concentration and ratio of chlorophyll a and b explained most of the variance (58.6%), thereby linking a specific combination of traits to productivity. These traits and their responses to light were affected by heterosis, as indicated by the clone-treatment interaction, particularly for the clone's moderate productivity. The top-performing clones were little sensitive to illumination due to efficient photosystems. Nevertheless, illumination with wider spectral composition had generally positive effects on plantlet performance. Accordingly, clone-specific illumination protocols and luminaries capable of it are advantageous for the efficiency of micropropagation of hybrid aspen.

Keywords: LED; chlorophyll; leaf area; micropropagation; shoot length.

Figure 1

Relative variance explained by the principal components of the studied anatomical and physiological variables (means of experimental units, i.e., clone by treatment) of hybrid aspen (A), loadings of the variables (B) and scores of the experimental units (C). In C, ellipses indicate 95% confidence intervals of scores for clones with contrasting filed performance (high, intermediate, and low). Variable codes: NI—number of internodes; LTI—length of third internode; MSL—main shoot length; TSL—total shoot length; MLA—mean leaf area; TLA—total leaf area; CAR—concentration of carotenoids; CHLA—concentration of chlorophyll a; CHL B—concentration of chlorophyll b; CHLA+B—total chlorophyll concentration; CHLA/B—chlorophyll a and b ratio; Fv/Fm—maximum quantum yield efficiency; PI—performance index; CAT—catalase activity; POX—peroxidase activity.

Figure 2

The estimated marginal mean values and their 95% confidence intervals (black dots and whiskers) for total area of leaves per plantlet (A), chlorophyll a and b ratio (B), and the total concentration of chlorophyll a and b (C) according to light treatments and clone of hybrid aspen in vitro. Similar letters above the data indicate lack of significant differences at α = 0.05. Points in the background depict the mean values of propagation jars/test tubes. The clones are ranged according to their field performance from the highly productive (clones No.: 4 and 44) to low productive (clones No.: 21 and 5) clones.

Figure 3

Spectral composition and photon count of each lighting treatment: (A) fluorescent tubes (FL); (B) Red and Blue (RB), max photon count at 655 and 440 nm; (C) Red, Green and Blue (RGB) max photon count at 655, 520, 440 nm; (D) Red, Green, Orange, Blue (RGBYO), max pho-ton count 655, 535, 625, 445 nm.