Which symptom indicates a possible bacterial disease?

The symptom of gummy exudates from the stems is a strong indicator of a bacterial disease. This particular symptom occurs when bacteria infect plant tissues, often leading to the production of a sticky or gummy substance as the plant responds to the infection. This exudate can be a result of the bacterial action degrading the plant tissues, and it often contributes to the further spread of the disease, as the exudate may contain bacteria that can infect healthy neighboring plants.

In contrast, browning of leaf tips is a symptom that can arise from various environmental stressors, such as dry conditions or nutrient deficiencies. Powdery mildew on leaves is primarily a fungal disease characterized by a white, powdery fungal growth and does not relate to bacterial infections. Soft rot of tubers, while also a sign of bacterial disease, typically refers to the breakdown of plant tissues in the roots or tubers specifically, rather than the visible exudates from stems. Therefore, while both soft rot and gummy exudates indicate bacterial involvement, the presence of gummy exudates is a more distinct symptom linked directly to bacterial infections in stems.