Choosing the right citrus rootstock is a crucial agronomic decision for the success of a new citrus orchard. Even when cultivating a few citrus plants in your garden, selecting nursery stock with rootstock resistant to diseases and challenging environmental conditions can make the difference between success and failure in cultivation.
In this article, we provide an overview of the most common citrus rootstocks used in organic citrus farming, highlighting their advantages and disadvantages.
Characteristics of the Rootstock
In citrus farming, the propagation technique commonly used in nurseries is grafting. The most frequently practiced grafting technique is the crown graft, which is done from April to June. It involves the use of scions stored in the refrigerator (1-3 months) at a temperature of 14-15 °C until the detachment of the petiole, and 10 °C thereafter. Until a few decades ago, citrus rootstock was chosen to facilitate the multiplication of cultivars. By doing so, a rootstock with good resistance to asphyxia and attacks by fungal diseases of the genus Phytophthora spp. was obtained. These fungi are highly dangerous and lead to diseases of the root system and fruit. They are generally known as collar rots (Armillaria mellea) or fruit rots.
Today, in addition to this important characteristic, other factors are considered when choosing citrus rootstock, such as:
- Adaptation to the chemical and physical properties of the soil;
- Climate of the cultivation environment;
- Good grafting compatibility;
- Resistance or tolerance to: citrus tristeza virus, citrus canker, xyloporosis, cristacortis, psorosis, and exocortis viroid;
- Resistance to frost.
It is also important to note that, for the purchase of grafted citrus plants from a nursery, you should contact certified operators. They can guarantee the sale of plants free from viruses.
Most Common Citrus Rootstocks
Now let’s take a look at the most common citrus rootstocks. In this brief list, we’ll analyze their advantages and disadvantages.
Bitter Orange (Citrus aurantium)
In the past, the most commonly used rootstock for citrus was bitter orange, specifically Citrus aurantium. It is a tree that has great resistance to Phytophthora spp. As a rootstock, it also has excellent compatibility with most citrus cultivars. However, due to the spread of citrus tristeza virus in areas where the virosis has become endemic, there has been a progressive abandonment of bitter orange as a citrus rootstock. The experience of other countries, such as Spain, where the virus has caused the death of millions of citrus trees, has led farmers to be cautious in its exclusive use. Fortunately, in Italy, there hasn’t been an endemic spread of the disease, but there have been numerous outbreaks. Another problem with bitter orange is that in specialized citrus farming, where replanting is frequent, the tree may face development difficulties due to the phenomenon known as “decline”.
The Citrange Troyer rootstock has the advantage of good compatibility with sweet orange, mandarin, and grapefruit. It induces high productivity and strong canopy vigor. Additionally, it is tolerant to tristeza, psorosis, xyloporosis, and Phytophthora. On the downside, it is susceptible to Fusarium and exocortis. It also shows grafting incompatibility with the “Eureka” lemon tree and the tangelo “Mapo”.
The Citrange Carrizo rootstock shares the same positive characteristics as Troyer. It also tolerates cold better and produces more when grafted onto the “Moro” variety. However, it is sensitive to Fusarium and exocortis.
Flying Dragon is a dwarfing citrus rootstock that allows control over excessive vigor. For example, it works well with the “Tarocco” cultivar. It also enhances fruit pigmentation, improving the final product’s quality. It has good resistance to cold, Phytophthora, and Fusarium. On the downside, it is unsuitable for calcareous, excessively moist, and saline soils. This rootstock is also sensitive to exocortis.
The advantages of Alemow citrus rootstock include good compatibility with lemon and clementines. It adapts well to all types of soil, including calcareous and highly saline soils. Among its disadvantages, it has the drawback of transmitting sensitivity to heat and citrus canker to the scion. It is also susceptible to tristeza and xyloporosis. The fruits it produces have thin peels.
Poncirus trifoliata citrus rootstock is one of the most widespread in modern citrus farming. It has excellent resistance to major diseases and viroses. It also fares well against collar rot and citrus nematodes. It has good compatibility with mandarins, sweet oranges, and grapefruits. It imparts excellent cold resistance to the scion and adapts well to moist soils.
On the downside, it has poor grafting compatibility with lemon and the “Mapo” tangelo. Sometimes, it leads to more vigorous growth of the subject compared to the graft. It doesn’t tolerate soils with an active calcium percentage exceeding 3-4%.
Citrumelo Swingle citrus rootstock has excellent cold resistance, which it imparts to the grafted cultivar. It is used in combination with sweet orange, showing excellent resistance to tristeza, exocortis, psorosis, xyloporosis, woody gall, and nematodes. However, it does not adapt well to calcareous soils, with a maximum tolerance of 3-4% active calcium. It is sensitive to excess moisture, water deficiency, and excessive soil salinity.
Citrange 35 rootstock imparts excellent resistance to Phytophthora spp. and citrus nematodes to the grafted citrus. It has good tolerance to any calcium that may be present in the soil, as well as tristeza, psorosis, and xyloporosis. On the downside, it is sensitive to exocortis.