Spencermartinsia viticola

Spencermartinsia viticola is an ascomycete fungus that belongs to the kingdom Fungi. It has been identified as an emerging pathogen involved in the complex of grapevine trunk diseases (GTDs), which are significant threats to viticulture worldwide.

This pathogen lives endophytically within the wood tissues of the grapevine, slowly colonizing the vascular system. Its biological characteristics include the ability to survive in a dormant state until conditions favor the development of reproductive structures.

The fungus is primarily spread by airborne conidia and spores that are released during rainfall. These spores land on fresh pruning wounds, which are the main entry points for the pathogen to establish itself in the host plant.

Identification of Spencermartinsia viticola in the field is difficult because the symptoms often overlap with those of other trunk disease pathogens like Phaeoacremonium or Neofusicoccum species.

Molecular diagnostic techniques, such as specific PCR assays, are required to accurately distinguish this fungus from other wood-decaying organisms. Understanding its association with other fungi helps in predicting the severity of the infection.

The primary host for Spencermartinsia viticola is the grapevine (Vitis vinifera). The pathogen attacks the permanent woody parts of the vine, specifically the trunk and the permanent cordon structures.

The fungus disrupts the vascular tissues, specifically the xylem vessels, which impairs the transport of water and nutrients to the canopy. This damage significantly reduces the physiological capacity of the vine to maintain healthy growth.

As the infection progresses, it causes internal wood necrosis, which weakens the structure of the vine. Over time, these infected parts become brittle, leading to the permanent decline or death of the grapevine.

The economic impact of this pathogen is severe, as it leads to the premature removal and replacement of entire vineyard blocks. It reduces the productive lifespan of the vine and causes substantial yield losses.

In hot and dry conditions, the weakened vascular system of an infected vine can fail completely, leading to the sudden collapse of the plant, a condition often referred to as apoplexy.

The internal symptoms of the infection are visible when cutting into the wood of an infected vine. Cross-sections often reveal dark, wedge-shaped necrotic lesions or spotted patterns in the woody tissue.

External symptoms on the leaves are characterized by interveinal chlorosis and necrosis. These patterns often create a mottled or "tiger-striped" appearance, followed by the rolling and premature shedding of the leaves.

Clusters on infected vines may show signs of poor ripening, uneven berry size, and shriveling. In some cases, the rachis of the cluster turns brown and dries up, leading to fruit loss before the harvest.

During the spring, infected vines often show delayed or uneven bud break. New shoots may appear weak, short-internoded, or exhibit stunted growth, which is a clear indication that the vine is under severe stress.

• Dark necrotic lesions visible on cross-sections of the wood
• Interveinal chlorosis and leaf necrosis (tiger stripes)
• Stunted shoot growth and delayed bud development
• Premature fruit shriveling and cluster drying
• Sudden collapse of the vine during the peak growing season

Strict sanitation measures are crucial for managing this pathogen. Pruning tools must be disinfected frequently using appropriate chemical solutions to prevent the mechanical transmission of spores between plants.

Affected wood should be cut back until healthy, non-discolored tissue is revealed. All removed plant material should be burned or buried away from the vineyard to reduce the amount of inoculum present in the area.

Protecting pruning wounds is a critical management practice. The application of wound sealants or biological fungicides immediately after pruning acts as a protective barrier against spore colonization.

Ensuring the use of high-quality, disease-free nursery material is the foundation of a healthy vineyard. Rigorous inspection of cuttings and rootstocks helps prevent the early introduction of Spencermartinsia viticola.

Integrated vineyard management, including proper irrigation and balanced fertilization, helps the vine maintain its own defense mechanisms. Maintaining vine vigor is essential for minimizing the impact of trunk diseases.