Importance of propagative material in vine production

The national wine industry, with the objective of obtaining gains in competitiveness, has sought grape production from winegrowers associated with the quality of raw materials. The growing internal demand for whole grape juice has required the achievement of greater productivity per plant over time, but with rationalization of costs and resources. The production of fine wines has established greater rigor in the quality of the grapes processed.

The quality of the plant material that originates the vines is the key factor in establishing the productive potential of a crop. Thus, among the agricultural practices considered strategic, the production of vine seedlings currently stands out. It is common sense in the wine sector that an efficient reconversion of the production matrix will only be complete once the seedlings used are added to technological innovations.

The technical basis for obtaining vine seedlings is already known and widely disseminated among producers and nurseries. However, innovation in production is still little explored. The basis of this innovation comes from the supply of propagative materials with the so-called “superior sanitary, genetic and agronomic qualities”. And these are the ones that, due to lack of knowledge or lack of legal force, are often ignored by seedling producers, who fail to add value to your product.

The use of vine seedlings with genetic and sanitary quality is an essential condition for remaining in the activity with economic viability and competitiveness compared to external competitors. The longevity of vineyards is especially related to the occurrence of phytosanitary problems. Over the years, Brazilian winemaking has faced the emergence of several phytosanitary problems, which are proving to be the main technological obstacle to the continuity of the activity.

Therefore, both professional nurseries and rural producers must review the concept of seedling production. Although there are still no official quality and identity standards for seedlings, the wine sector has increasingly expected to guarantee the quality of the seedlings produced. Among the most demanded quality criteria, special attention has been given to phytosanitary aspects, highlighting care to prevent the spread of fungi, viruses and insects among the seedlings. This care begins with the visual assessment of the seedlings, since in a batch of seedlings with a uniform morphological presentation, there is already an indication that the production system was applied efficiently.

The following morphological pattern represents the visual appearance of the seedling with superior quality: rootstock (length of at least 30cm and diameter between 1,5cm and 2,5cm); grafting (good welding, without cracks or thickening); graft (single shoot, at least 0,3cm in diameter and at least two buds); root system (symmetrical, with one level of roots, with at least three roots and pruned to at least 10cm). An example of a seedling in this pattern is seen in Figure 1, while Figures 2 and 3 demonstrate seedlings with non-standard root systems and grafting, respectively.

However, in addition to the morphological pattern, the phytosanitary quality, which often cannot be identified visually, is what should receive the greatest attention from the seedling producer. Essentially, there are three stages of the nursery that must be monitored: 1) obtaining the propagative material for seedlings from the seedbeds; 2) grafting the scion variety onto the rootstock and 3) rooting the seedlings in beds.

There are several variations in techniques throughout the stages. In seedlings produced by professional nurseries registered with Renasem/Mapa, there is a high production scale, as they use mechanized equipment for grafting, forcing and rooting (Figure 4). However, especially in family smallholdings, with an emphasis on ecologically based systems, it is still common to produce seedlings on the property, using manual grafting and field rooting (Figure 5). Regardless of the producer's profile, the sanitary basis for obtaining superior quality materials is the same.

The acquisition or formation of quality seedlings is an initial key point for controlling diseases that cause vine death. The use of infected seedlings has caused the spread of diseases to areas previously free of the disease. The lack of awareness on the part of rural producers and some nurserymen makes the problem extremely serious, since in addition to contributing to the spread of pathogens, it involves spending on the uneconomical maintenance of plants that will have to be, sooner or later, eliminated, in addition to new expenses with replanting and the delay in financial returns to the producer. Therefore, the short-sighted view in which the seedling is a production factor that is not very relevant within the business must be completely abandoned.

Several phytopathogenic fungi can attack the vine, causing losses to a greater or lesser extent. Part of it is often disseminated via contaminated vegetative material, resulting in weaker plants, with less vigor, less production, smaller than normal leaves, chlorotic, reddening between the veins, withering in the aerial part, progressing to decline and death (Figure 6) . Among the fungal diseases that cause decline and death of vines, the following stand out: fusariosis (Fusarium oxysporum f.sp. herbemontis); black foot (Cylindrocarpon destructans); chocolate (Phaeoacemonium sp. It is Phaeoacremoniella sp.); eupithiosis (Eutypa lata); downward rot (Botryosphaeria sp. Neofusicoccum sp. It is Lasiodiplodia theobromae); collar rot (Xyllaria sp.), among others. These pathogens are a major threat to the establishment of modern and competitive viticulture. The lack of information and/or inaccurate diagnosis has led many producers, after noticing the symptoms, to use fertilizers as a way to correct the problem, mistakenly thinking it was a nutritional deficiency, whereas in fact the cause is biotic, or be caused by a phytopathogenic agent.

As these fungi are transmitted via vegetative material, producers or nurseries need to visually monitor the mother plants periodically in order to avoid collecting cuttings or buds from plants with the presence of disease symptoms. Complementary analyzes can be carried out in Phytopathology laboratories, sending grapevine samples for the detection of phytopathogenic fungi within the tissues. Plants with symptoms of downward rot or eutypiosis must be recovered, through drastic pruning, to eliminate all rotten tissue, and the cuts protected with a fungicide-based paste. Only then can this recovered plant be a candidate for the mother plant, as long as after monitoring the presence of symptoms is not detected again. For other diseases caused by soil fungi, it is recommended to eradicate plants with symptoms.

Other recommended control measures are: not installing the nursery close to commercially used vineyards; use soil in the nursery that is free from phytopathogenic fungi that cause plant decline and death and that has not been cultivated with vines for at least three years; treat the base of the cuttings with a fungicide solution (tebuconazole or methyl thiophanate) before direct contact with the soil or substrate; in organic or agroecological systems, protection can be carried out with Bordeaux mixture or Trichoderma; after grafting, spray or brush the tissue region with a fungicide solution to prevent the entry of fungi that cause dieback; Discard seedlings that show symptoms of root rot or darkening of roots and/or internal rot at the base.

In the case of grapevine viruses, the infectious process will result in a drop in productivity and production quality, reflecting on the profitability of the crop. Symptoms associated with viral infection in grapevines are continuous and gradual loss of plant vigor, reduced production, abnormal coloration (reddening or yellowing) of leaves, leaves with an atypical appearance (curled edges, rough texture and blistering on the surface of the leaf blade), irregular sprouting of branches, thickening and irregular maturation of branches, presence of cannelures in the wood (grooves under the bark of the trunk) (Figure 7A-B) and trunk bark with an altered appearance (thick and with cracks) (Figure 7C-D) , in addition to irregular ripening and lower sugar content in the fruits. It is important to highlight that the virus-infected vine will not always exhibit noticeable symptoms, as the infection may be latent in some commercial cultivars. However, even in these cases the presence of the virus can cause harm.

Controlling grapevine viruses is only viable in the field through the use of healthy propagative material from the rootstock and the producing cultivar (scion). When implementing or renewing a vineyard, it is recommended that “certified” seedlings or propagation material be purchased and planted, i.e., guaranteed to be in good health. This type of material can be obtained from official bodies that develop conservation programs. production of virus-free vine propagative material or in nurseries that multiply healthy material under the control of official bodies.Another option is to acquire seedlings through import, observing the legislation relating to this procedure.

In a specific situation, it is the winegrower who prepares the seedling that will be planted on his property. In this case, the winegrower must carry out careful visual inspection, periodically and throughout the year, in the vineyard from which he intends to remove the propagative material, selecting plants with good health appearance, vigorous, productive and with good quality grapes. The observation of symptoms, which may be associated with viral infection, disqualifies the plant as a donor of good quality propagative material. This process is not a total guarantee that the seedlings formed will have good phytosanitary condition, as the selected “mother” plants may not exhibit symptoms of viral infection depending on the type of genetic material (cultivar), environmental conditions, the virulence of the isolate or viral species, plant development stage, among other factors.

Acquiring seedlings from a reputable source gives greater assurance that they are not affected by viruses, diseases that are very difficult to recognize when the seedlings are acquired. If the seedling is contaminated, this will probably only be detected in the vineyard some time after planting. Therefore, the only technical solution would be to eliminate the infected plant and replant a seedling in good health condition, since, once infected by a virus, it is impossible to cure a plant in the field.

The recommendation that the producer use propagative material (cuttings, buds, seedlings) with superior health is valid for both the rootstock cultivar and the graft cultivar (scion). Viruses are systemic pathogens, that is, they have the ability to move from the rootstock to the scion and vice versa and, consequently, the healthy part of the seedling will be infected from the sick part.

Rootstocks, even when affected by viruses, rarely show symptoms of the disease, that is, they present almost normal development, making visual identification of infected plants impossible. Damage to the seedling, when using infected rootstock, will only be observed in the vineyard some time after planting, when the canopy vegetation, which is normally sensitive to viral infection, begins to exhibit symptoms of the disease. After this observation, there will be no further possibility of control other than replacing the seedling.

Thus, the main way viruses are spread is through infected propagative material, during the seedling formation process, regardless of the grafting method. To date, there is no evidence that the viruses that infect grapevines are transmitted mechanically, that is, that they can be transmitted by cultivation tools.

Until some time ago, it was assumed that the spread of grapevine viruses occurred exclusively through infected propagative material, mainly through rootstocks that did not show symptoms. However, studies have shown that some species of mealybugs act as virus vectors in grapevines. Since then, in several wine-growing countries around the world, reports have emerged of the natural spread of viruses in vineyards by different species of mealybugs (pseudococcidia). The control of virus vector insects is a difficult topic to approach, due to the range of variables involved in the viral transmission process and, currently, constitutes a challenge for global viticulture.

In addition to viruses, insect pests such as the earth pearl (Eurhizococcus brasiliensis), phylloxera (Daktulosphaira vitifoliae) and mealybugs can be transmitted with the seedling and cause significant losses in the productive potential of the future vineyard. To monitor these pests, the seedling producer must pay attention to some aspects. The ground pearl, being the pest of greatest economic importance in vine cultivation, must have its dispersion between regions eliminated. In this case, the greatest risk occurs when offering seedlings in the form of clods. As for phylloxera, when harvesting the seedlings, the presence of nodosities, tuberosities and hypertrophies in the roots must be observed, as they are symptoms related to its occurrence. Finally, it should be noted that the best control of insect pests, in the seedling production process, will occur throughout the vegetative period. This is the case of phylloxera structures, which can be observed on leaves, branches and shoots during the summer (Figure 8) and the presence of pearl cysts on the roots (especially in mother plants) from the beginning of spring.

Legend of the figures:

Figure 1 - Seedling obtained by mechanical grafting with morphological pattern (Photo: Daniel Santos Grohs)

Figure 2 - Seedling obtained by manual grafting with a root system outside the morphological standard (Photo: Daniel S. Grohs)

Figure 3 - Detail of graft performed manually outside the morphological standard (Photo: Daniel S. Grohs)

Figure 4 - Seedlings grafted and rooted in a typical production system applied by professional nurserymen (Photo: Daniel S. Grohs)

Figure 5 - Rooted seedlings in a typical production system applied by winegrowers on the property (Photo: Daniel S. Grohs)

Figure 6 - Fungal diseases that compromise the development of grapevine plants. Blackfoot (A); fusariosis (B); chocolate (C) and downward rot (D) (Photos: Lucas da R. Garrido)

Figure 7 - Vines affected by viruses. (A) rootstock cultivar Paulsen 1103, normal appearance of the wood in a healthy plant and (B) longitudinal indentations typical of the trunk flutes (visualized after removing the bark), corresponding to the place where the bark penetrates the wood, impairing the functioning normal of the sap-conducting vessels; (C) cross-section of branches from a healthy vine and (D) from a vine infected with the rugose complex virus, showing thickening of the bark and cannelures (Photos: Thor V. M. Fajardo)

Check out the article in issue 83 of Revista Cultivar Hortaliças e Frutas.