What symptom can indicate that a plant is infected with Cucumber mosaic cucumovirus?

The presence of a mosaic pattern is indeed a classic symptom associated with Cucumber mosaic cucumovirus (CMV) infection in plants. This symptom manifests as irregular light and dark green areas on the leaves, resembling a mosaic, which can be attributed to the virus affecting the plant's chlorophyll production. The disruption in chlorophyll distribution causes these distinct patterns, making it a key visual indicator of CMV infection.

In contrast, while leaf dropout can occur in various diseases, it is not specifically associated with CMV. Discoloration of roots is typically indicative of other issues such as root rot or nutrient deficiencies rather than viral infections. Excessive flowering is also generally not a symptom of CMV infection; instead, it might be a response to stress or environmental factors, but does not directly relate to the virus's typical symptoms. Thus, recognizing the mosaic pattern is essential for diagnosing Cucumber mosaic cucumovirus effectively.