Citrus canker is a bacterial disease caused by Xanthomonas citri (syn. X. axonopodis pv. citri). It produces raised necrotic lesions on leaves, fruit, and stems, causing defoliation and reduced yield. It spreads via rain splash and contaminated tools. No viral or fungal causal agent.
Explanation:
Lateral meristems—vascular cambium and cork cambium—are responsible for secondary growth, increasing the girth (diameter) of dicot stems and roots. Apical meristem at root and shoot tips causes primary growth in length. Intercalary meristem at nodes helps in elongation in grasses. Epidermis is a protective outer layer. Secondary growth is absent in most monocots due to lack of vascular cambium.
Explanation:
Max Theiler developed the attenuated yellow fever vaccine (17D strain) in the 1930s, winning the Nobel Prize. Pasteur rabies, Jenner smallpox, Salk polio.
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