Comparative branching order and root anatomy of clonal and seed-grown avocado trees (Persea americana Mill.)

Characterizing roots according to their branching order and anatomy is a useful approach for identifying functional differences within and among root systems. In this study, the root branching order and the anatomy of each root order (stele and cortex area) were examined in two-year-old “Duke 7” avocado (Persea americana Mill.) trees propagated by seed and by clonal techniques. The root systems were found to have three different root orders that exhibited differences in the occurrence of secondary xylem. Fine roots (first- and second-order roots) presented only primary growth, whereas the main roots (third-order roots) exhibited secondary growth. Transverse sections of roots from the different orders showed pentarch, hexarch or heptarch tracheal element distributions. Newly emerged, long, unbranched pioneer roots were observed only in the clonal trees and showed particular anatomical features, such as a larger diameter and a proportionally greater cortex area than other roots, as well as primary growth. Additionally, significant differences were found between clonal and seedling trees in the stele area of third-order roots; clonal propagation resulted in larger stele areas in this type of root. Our results suggest that propagation methods influence the presence of new pioneer roots and the anatomy of third-order roots; clonal root systems branch more extensively than seed-grown root systems and develop a vascular system with a larger transport capacity

Micropropagation of <i>Citronella mucronata</i> D. Don, a Vulnerable Chilean Endemic Tree Species

Citronella mucronata (C. mucronata), a tree species endemic to Chile, has become threatened in its natural habitat and is currently listed as vulnerable. Tree population parameters have deteriorated due to indiscriminate logging and other anthropogenic activities, warranting research on mass propagation as a means of recovery. This study, unprecedented for this native species, has developed a successful method for its micropropagation. The objective was to establish a protocol for in vitro propagation of C. mucronata to produce large quantities of high-quality seedlings in an accelerated plant acquisition process. The best results were achieved by growing explants on Murashige and Skoog (MS) basal culture medium supplemented with 4.44 μM 6-benzylaminopurine (BAP) and 14.76 μM indole-3-butyric acid (IBA). Explant survival rate was 78 %, the average shoot length reached 3.2 cm, the number of lateral shoots was 3.9, and rooting rate was 60%. Furthermore, stimulation with red and blue light in a 1:2 ratio, supplemented with 14.76 μM IBA, improved the rooting rate to 93%. The survival rate of rooted explants reached 100% in the acclimatization stage when using peat and perlite substrate (1:1 v/v)

Clonal propagation of the avocado: effects of the rooting step on graft union formation and development

The etiolation and layering technique that is used on avocados has two critical steps, namely, the rooting of clonal rootstock and graft union formation between the commercial variety and clonal rootstock. This study analyzed the rooting step of the clonal rootstock regarding its influence on graft union formation and development. The optimum times for grafting the commercial variety onto clonal avocado rootstock were determined under two greenhouse conditions, heating and no heating. The results showed that under greenhouse conditions without heating, there was higher survival (%) in plants that were grafted 60 days after the rooting steps in the clonal scion, and, in the experiments in a heated greenhouse, the highest survival rate (%) was observed in plants that were grafted 15 days after the rooting treatments. For both assays, the lowest survival rate was observed for grafts performed 30 days after the wounding and auxin application process. In histological cross sections of rootstocks at the wounding zone and in auxin treatments, a large number of emerging adventitious roots were developed at 30 days.La técnica de etiolación y acodo utilizada en palto presenta dos etapas críticas: el enraizamiento del portainjerto clonal y el prendimiento del injerto entre la variedad comercial y el portainjerto clonal. En este estudio se evaluó la influencia de la fase de enraizamiento del portainjerto clonal sobre el prendimiento y desarrollo del injerto. Definiendo los momentos óptimos para realizar la injertación de la variedad comercial sobre el portainjerto clonal de palto, en dos condiciones de invernadero con y sin calefacción. Los resultados mostraron para las condiciones de invernadero sin calefacción, mayor prendimiento (%) en plantas injertadas a los 60 días después de los pasos de enraizamiento en la púa clonal, mientras que en el ensayo realizado en invernadero calefaccionado el mayor prendimiento (%) se observó en plantas injertadas a los 15 días después de realizados los tratamientos de enraizamiento. Para ambos ensayos, el menor prendimiento (%) se observó en plantas injertadas a los 30 días después de realizado el lesionado y la aplicación de auxinas. En cortes histológicos realizados al portainjerto, en la zona del lesionado y aplicación de la mezcla auxínica, a los 30 días, se observó gran cantidad de raíces adventicias emergiendo