Where can root rot decay be observed in a plant?

Root rot decay is specifically associated with the root system of the plant, often beginning at the crown or base where the roots meet the stem. This condition is typically caused by soil pathogens, which thrive in moist, poorly drained conditions. When root rot occurs, it can spread downward from the crown and extend throughout much of the root system, affecting the plant's ability to absorb water and nutrients effectively.

Observing decay in this manner reflects a systemic issue that impacts the entire root structure, rather than being localized only at the soil surface or just at the tips of the roots. Additionally, while other plant parts such as leaves and stems might show signs of stress due to the root system's decline, those areas do not directly exhibit root rot decay itself. Thus, the option indicating that root rot can extend from the crown downward and affect most of the root system accurately describes the characteristic spread of this problem within the plant structure.