Maintaining the Foliage of the Rootstock Impacts the Quality of the Flowering Stem Developed from the Bud Grafted in Cut Roses

Cut roses (Rosa L. hybrida) are acknowledged as the most popular cut flower due to its attractiveness and variety of forms and colors. Rose propagators usually remove the foliage from the rootstock as soon as it is bud-grafted, however, no research has been performed to demonstrate weather this common practice is beneficial for plant growth. If not removed, the foliage of the rootstock may be a source of photosynthates for the developing bud until the grafted plant has formed its own foliage and is able to meet its demands. The present research was performed to determine the influence of the maintaining the foliage of the rootstock for a longer period of time on the growth, nutrient status and total soluble sugars (TSS) of the flowering stem. Buds of cv. Freedom were grafted on cuttings of Rosa montezumaerooted on a volcanic rock-based medium placed on black polyethylene bags and grown in hydroponics. Treatments consisted on maintaining the foliage of the rootstock for 8, 28, 48 and 68 days after grafting (DAG). Length and diameter of the flowering stem that developed from the grafted bud was measured when the flower bud was visible; plants were harvested and separated into stems, leaves and flower buds for determination of nutrient status and TSS. Results showed that flowering stems were twice as long when the foliage of the rootstock was maintained for 68 DAG. Nitrogen, phosphorus and calcium concentration on stems, foliage and flower bud increased after 28 DAG but tended to decrease afterwards. Potassium concentration tended to decrease in stems and foliage whereas it exhibited no consistent tendency in the flower buds.  Magnesium increased in the leaves from grafting time up to 48 DAG but decreased thereafter. Concentration of TDS in the stem and flower bud increased by two fold at 68 DAG. We conclude that maintaining the foliage in the rootstock for a longer period of time enhances growth of the flowering stem; nutrient status and TDS increased from grafting time up to 28 DAG while stem length and diameter were increased when the foliage was maintained in the rootstock for 68 DAG.