M4
| Variety Passport | |
| Country of origin: | Italy |
| Breeder: | CREA (Italy) |
| Variety number VIVC: | 25507 |
| Prime name: | Milano 4 |
| Year of obtaining / registration: | Admitted to the National Register of Grape Varieties of Italy on May 15, 2014 |
| Pedigree given by breeder: | 41 B (Vitis Vinifera × Vitis Berlandieri) × Resseguier n°4 (Vitis Berlandieri). |
| Rootstock type: | Phylloxera-resistant, Salt-tolerant |
| Data Sources: | Vitis International Variety Catalogue (VIVC), Registro Nazionale delle Varietà di Vite (Italy) |
| Agrobiology | |
| Vigor: | very vigorous |
| Lateral shoot formation: | strong |
| Flower type: | female |
| Salinity tolerance: | resistant |
| Drought tolerance: | resistant |
| Root phylloxera susceptibility: | 1 point (highly resistant) |
| Rooting ability: | medium |
| Graft compatibility with Vitis vinifera: | medium |
| Recommended soil types: | Recommended for soils with highly drought-prone conditions, high chloride levels, and a moderate risk of iron chlorosis. |
| Ampelographic overview |
Origin History and Agronomic Importance
The M4 grapevine rootstock was bred in Italy by selectionists at the Council for Agricultural Research and Agricultural Economy Analysis (CRA) and officially admitted to the national register of varieties on May 15, 2014. The parental pair of the rootstock was obtained by crossing a complex interspecific hybrid 41 B (Vitis vinifera × Vitis berlandieri) as the maternal form and a pure species Vitis berlandieri (clone Resseguier n°4) as the paternal component. The primary breeding advantage of this grapevine rootstock lies in its exceptionally high resistance to drought and high salinity tolerance (chloride resistance). Based on these combinations, the M4 rootstock variety is recommended for drought-prone viticultural regions, as well as for saline soils and areas with a moderate risk of iron chlorosis. Early dates of budburst, medium dates of flowering, and medium dates of wood maturity are recorded for this variety.
Ampelographic Description of M4 Rootstock Variety
The morphological characteristics of the rootstock were recorded in detail by experts during the official state evaluation according to the international OIV system:
- Young shoot (tip): The young shoot tip is completely closed. A distinct diffuse anthocyanin pigmentation of high intensity is present on the tip. Prostrate (long) and erect (short) hairs are completely absent on the tip. On the nodes of the young shoot during the flowering period, erect and prostrate hairs are either completely absent or extremely sparse, and they are completely absent on the internodes. Tendrils have a medium length, forming sequentially in groups of two or fewer. Developing internodes are long with a medium diameter.
- Young leaf: The upper surface of the fourth formed leaf blade features a characteristic bronze coloration. Both prostrate and erect hairs are completely absent on the lower surface of the young leaf (both between the veins and on the main veins themselves).
- Mature leaf: The leaf blade is distinguished by a small size and a pronounced heart-shaped (cuneiform-cordate) form. The leaf is entire and consists of a single lobe. The upper surface of the blade features a light shade of green. Anthocyanin pigmentation of the main veins on the upper surface of the blade extends up to the second bifurcation, while on the lower surface, it appears locally, exclusively at the petiole point. The profile of the blade in cross-section is flat, with no depression, blistering, or dimpling of the tissue. The teeth are small and short relative to the width of their base, showing a mixed shape with straight and convex sides. The petiole sinus is very open, U-shaped at the base, with no morphological anomalies. Lateral sinuses are completely absent. On the lower surface of the leaf, a very low density of prostrate hairs is present between the veins, while erect hairs are absent. On the veins themselves on the lower side, a very low density of prostrate hairs and a low density of straight erect hairs are recorded. On the upper surface of the leaf, prostrate hairs along the main veins are absent, but rare erect hairs of low density are detected. The petiole is slightly shorter than the median vein and is completely devoid of prostrate and erect hairs.
- Woody shoot: The canes are elliptical in cross-section. The surface of the shoot is smooth, completely devoid of hairs and lenticels.
- Flower: The M4 rootstock variety develops inflorescences with a functionally female flower type.
Features of Viticultural Nursery Practice
The M4 grapevine rootstock is characterized by a very high shoot vigor in mother vineyards and a high intensity of lateral shoot development during the growing season. The agronomic productivity of mother vineyards in terms of high-quality mature wood yield per hectare is rated as high. According to statistical nursery data, the production of certified and base planting material of this variety shows an annual upward trend. The rooting capacity of cuttings in commercial field nurseries is medium. When conducting bench or field grafting with scion components of the European-Asian grapevine Vitis vinifera, this rootstock demonstrates medium parameters of callus formation intensity and successful graft union development.