How Bacterial Disease Affects Plum Trees: What We Learned from Years of Research in Brazilian Orchards

Figure 1. Dynamics of plum leaf scald disease symptoms and role of vectors in the transmission of Xylella fastidiosa.

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Xylella fastidiosa, a bacterial pathogen of global concern, infects a wide range of plants and causes severe diseases, including plum leaf scald (PLS) in Brazilian plum orchards. This pathogen spreads through xylem-feeding insects like sharpshooter leafhoppers, which acquire the bacteria from infected plants and transmit it as they feed on healthy trees (Figure 1). Once inside a plant, Xylella multiplies in the xylem vessels, obstructing water transport, which leads to visible symptoms and plant decline (Figure 2).

In our study, we monitored PLS spread and vector distribution across three Brazilian orchards (Figure 3) to clarify disease dynamics, evaluate pathogen dispersal patterns, and assess the impact of mechanical pruning on disease transmission.

Figure 2. Comparison between a healthy plum leaf (A) and an infected plum leaf (B).

Findings revealed considerable variation in disease incidence across locations. Disease incidence started at 0% and reached just 14% over five years, showing relatively low pathogen establishment. In contrast, other orchards had initial PLS incidences of about 5%, which escalated dramatically to over 80% by the conclusion of the study. The sharpshooter leafhoppers, vectors of Xylella fastidiosa, were denser near the ground; however, their distribution had equalized across heights. This shift in vector presence highlights potential seasonal or environmental influences on vector behavior, which may affect pathogen transmission within the orchard.

Figure 3. Description of the commercial plum orchards assessed, Brazil.

Spatial analyses demonstrated a clustered infection pattern with strong spatial dependence. This indicates that neighboring plants are more susceptible to infection, partly due to proximity to infected trees. The study also identified a pronounced border effect at the epidemic’s onset, where the pathogen appeared to enter primarily through orchard peripheries, likely carried by external vectors, underscoring the importance of perimeter monitoring (Figure 4).

Mechanical pruning contributed to pathogen dispersal along orchard rows. As pruning cuts can facilitate pathogen transfer from infected to healthy trees, we recommend disinfecting pruning shears between cuts to mitigate this risk. This research underscores the complex dynamics of Xylella fastidiosa and PLS, emphasizing the need for integrated disease management that combines vector control, sanitation practices, reducing PLS impact and protecting Brazil’s plum orchards.

Figure 4. Primary and secondary infection of Xylella fastidiosa in plum orchards.

TITLE IMAGE: One of the orchards assessed in this study.