Which of the following is a symptom of Citrus tristeza closterovirus?

The symptom identified as light green foliage is characteristic of Citrus tristeza virus (CTV), specifically linked with its impact on citrus trees. This symptom often manifests in the form of chlorosis, where the leaves are not fully green and exhibit a light green hue instead, indicating a disruption in chlorophyll production. This can lead to reduced photosynthesis efficiency and overall vitality of the plant.

In the context of CTV, light green foliage is usually associated with the tree's response to infection, reflecting an imbalance in nutrient distribution or a consequence of stress due to the virus affecting the plant’s ability to function properly. This symptom is important for recognizing the presence of the virus, as it may also be accompanied by other symptoms like stunted growth or the presence of abnormal fruit.

Symptoms like dark spots on leaves, wilting of roots, and pale yellow flowers may be indicative of other diseases or environmental stresses but do not specifically relate to the classic symptoms associated with Citrus tristeza closterovirus infection, making light green foliage the most relevant answer in this context.