Which of the following statements is true regarding signs of a plant disease?

The correct statement about signs of a plant disease is that they can sometimes require a hand lens or microscope to observe. This is accurate because signs refer to the physical evidence of a pathogen's presence on a plant, such as fungi, bacteria, or insect damage. While many signs, like fungal growth or mildew, can be seen with the naked eye, some signs may be microscopic in nature, making a hand lens or microscope necessary for proper identification.

To understand this better, it's important to differentiate between signs and symptoms. Symptoms refer to the reactions of the plant itself, such as wilting, leaf spots, or stunted growth. Therefore, it is not correct to say that signs are the reactions of the plant to disease, which describes symptoms.

While some signs may be easily identifiable, there are numerous cases where the subtleties of a pathogen's impact are so small that close examination is needed. Additionally, signs indeed do indicate the pathogen's presence, contradicting the idea that they do not reflect such information.