In vitro-and ex vitro-rooted microcuttings of Acer rubrum L. 'Red Sunset', Betula nigra L., and Malus × -domestiea Borkh 'McIntosh' were distinguished by several important anatomical and morphological properties which continued to regulate both root system and whole plant quality in later stages of production. In vitro microcuttings formed adventitious roots in greater number and more quickly than ex vitro microcuttings. Roots produced in vitro were characterized by extremely enlarged cortical cells and, consequently, had a much greater diameter than ex vitro roots. However, the vascular system of in vitro roots was underdeveloped (primary vascular tissues only) as compared to ex vitro roots, which produced vascular cambium and secondary growth during the same early stage of production. At least 50% of the post-transplant in vitro adventitious roots either died immediately, or temporarily persisted during acclimatization without producing any further growth. For the surviving in vitro-produced roots, the cortex partially collapsed after transplant, and new root extensions with ex vitro-like structure were produced. Only then did the in vitro portion of the root begin to form secondary vascular tissues. Shoots from in vitro treatments continued to grow vigorously during adventitious root initiation and during acclimatization, so that the plants were significantly taller and had a greater shoot area than those receiving comparable ex vitro rooting treatment. In vitro rooting led to a horizontal root morphology which continued to distinguish these treatments from ex vitro rooted plants during later stages of production, when anatomical differences in the roots could no longer be detected.

Microcomputerized video image analysis was adapted for rapid, objective, and non-intrusive quantification of shoot growth and development for plants growing in vitro. Custom-developed staging arrangements were essential to insure accurate viewing and representation of the plants in each of three standard culture vessels. Shoot length measurements from digitized culture images were strongly correlated with length measured manually ex vitro. Image analysis weighted density measurements of proliferating microcultures (even with irregular growth habits) provided a reliable indicator of shoot culture fresh weight. Nondestructive time course evaluations of growth rate and quality were demonstrated.Abbreviations: FW -fresh weight; WD -weighted density

Effects of three variables (vessel type, closure, and explant orientation) on microcutting quality were investigated using five woody species [low shadblow, Amefanchier spicata (Lam.) C. Koch (Syn. A. humilus Wieg.); red maple, Acer rubrun L. `Red Sunset'; border forsythia, Forsythia ×intermedia Zab. `Sunrise'; apple, Malus ×domestica Borkh. `McIntosh'; river birch, Betula nigra L.]. Uniform shoot explants were oriented vertically or horizontally in three vessel types (60-ml glass culture tubes, 200-ml glass baby food jars, and 350-ml polypropylene GA7 vessels) with and without a Parafilm seal. Visual density per explant obtained by image analysis was increased in larger vessel types, and significantly more shoots were produced from horizontally placed explants. Closure treatments influenced microshoot quality, but trends were species specific. Overall, horizontal explant orientation in larger vessels wthout parafilm maximized shoot response for most of the species studied. In vitro rooting of microcuttings was significantly enhanced in larger vessels.

The feasibility of using a whole plant microculture system coupled with image analysis to observe and quantify elusive root growth phenomena was demonstrated. Subtle differences in root initiation and growth rate for maple microcuttings inserted into three distinct rooting media were recurrently registered over the span of the rooting phase in terms of root length, number, and weighted density (equivalent to fresh weight) without disturbing the rooting environment. This method provided a non-intrusive time-course assay for take-all disease symptom expression on wheat lines (degree and rate of root lesion development), which paralleled the relative resistance rated in field plots. Although agar-solidified media had a relatively high light transmission (nearly 84% through 6.6 cm medium depth), roots could only be clearly perceived through a thickness of about 2 cm, and were often completely obscured when embedded to a depth greater than 5 cm.

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