What are the symptoms observed on infected leaves due to Stewart's bacterial wilt?

• A. Yellowish spots
• B. Dark patches
• C. Yellowish streaks running parallel to leaf veins
• D. Brown curling edges

Answer: (C)

The symptoms of Stewart's bacterial wilt, caused by the bacterium Pseudomonas syringae pv. glycinea, include yellowish streaks running parallel to the leaf veins. This characteristic is quite distinctive and helps in identifying the disease. The yellowing indicates that the bacteria are affecting the vascular tissues of the plant, leading to a disruption in the transport of nutrients and water, which in turn causes this specific symptom.

The yellowish streaks occur because the bacteria infect the leaf tissues, particularly the vascular bundles, eliciting a local response in the plant. As the infection develops, it becomes evident as these streaks, which are typically more noticeable on younger leaves. This symptom is important for diagnosing Stewart's bacterial wilt and differentiating it from other plant diseases that may display similar symptoms.

Other symptoms associated with plant diseases may include yellowish spots, which typically signify other issues like fungal infections; dark patches, which may relate to necrotic tissue; and brown curling edges, which are often indicative of different stress factors. However, for Stewart's bacterial wilt, the hallmark symptom is indeed the yellowish streaks, providing a clear indication of this specific bacterial infection.