Woodland strawberry axillary bud fate is dictated by a crosstalk of environmental and endogenous factors

Plant architecture is defined by fates and positions of meristematic tissues and has direct consequences on yield potential and environmental adaptation of the plant. In strawberries (Fragaria vesca L. and F. × ananassa Duch.), shoot apical meristems can remain vegetative or differentiate into a terminal inflorescence meristem. Strawberry axillary buds (AXBs) are located in leaf axils and can either remain dormant or follow one of the two possible developmental fates. AXBs can either develop into stolons needed for clonal reproduction or into branch crowns (BCs) that can bear their own terminal inflorescences under favorable conditions. Although AXB fate has direct consequences on yield potential and vegetative propagation of strawberries, the regulation of AXB fate has so far remained obscure. We subjected a number of woodland strawberry (F. vesca L.) natural accessions and transgenic genotypes to different environmental conditions and growth regulator treatments to demonstrate that strawberry AXB fate is regulated either by environmental or endogenous factors, depending on the AXB position on the plant. We confirm that the F. vesca GIBBERELLIN20-oxidase4 (FvGA20ox4) gene is indispensable for stolon development and under tight environmental regulation. Moreover, our data show that apical dominance inhibits the outgrowth of the youngest AXB as BCs, although the effect of apical dominance can be overrun by the activity of FvGA20ox4. Finally, we demonstrate that the FvGA20ox4 is photoperiodically regulated via FvSOC1 (F. vesca SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1) at 18°C, but at higher temperature of 22°C an unidentified FvSOC1-independent pathway promotes stolon development.

Morphological, physiological and metabolic comparisons between runner-like and sheet-like inbred lines of a colonial hydroid.

Hydractiniid hydroids display a range of morphological variation from sheet-like forms (i.e. closely spaced polyps with high rates of stolon branching) to runner-like forms (i.e. widely spaced polyps with low rates of stolon branching), thus exemplifying the patterns of heterochrony found in many colonial animals. A sheet-like and a runner-like inbred line of Podocoryne carnea were produced to investigate this heterochronic variation further. Selection on colony morphology at the time of the initiation of medusa production resulted in dramatic differences by the F5 and F6 generations. Compared with colonies of the sheet-like inbred line, runner-like colonies exhibited smaller sizes at the initiation of medusa production, more irregular colony shapes and diminished stolon development relative to polyp development. In addition to these differences in colony morphology, runner-like colonies also exhibited larger medusae and a greater amount of gastrovascular flow to the peripheral stolons. To assess differences in the metabolic capacity underlying this variaton in flow, the redox state of the polyp epitheliomuscular cells was measured using the fluorescence of NAD(P)H. In response to feeding-induced changes in gastrovascular flow, runner-like colonies show greater redox variation than sheet-like ones, plausibly corresponding to the greater amounts of flow generated by the former colonies relative to the latter. Perturbing the system with dilute solutions of 2,4-dinitrophenol similarly indicates that runner-like colonies contain more functionally oxidizable NAD(P)H. The correlation between gastrovascular flow and morphological differences supports the hypothesis that the former mediates the timing of colony development, perhaps in concert with the observed variation in the redox state of polyp epitheliomuscular cells.

ALTERNATE SOD PRODUCTION SYSTEM FOR ZOYSIAGRASS

A limitation to distribution of some field-grown sod is the time required to produce a saleable product rooted sufficiently to retain its shape when removed from the ground. Research for a more efficient sod production process was examined using sod segments planted at a 1:100 plant:planting area ratio in an aboveground soilless, root-restricting system. Combinations of 3 growth media, 2 rooting stimulants, and 2 fertilizers each at 2 rates were evaluated to determine the most rapid and optimal sod development for zoysiagrass. Treatments were rated weekly for percent cover, rate of stolon development, and rooting. Although treatments with rooting stimulants generally scored higher than other treatments for rooting and percent cover, these differences were not consistently significantly different from week to week. No significant differences occurred among treatments for stolon development ratings. After 16 weeks of growth, sod strength was greatest when the growth medium was a peat and vermiculite mixture.