What are the main agents responsible for causing disease in plants?

The main agents responsible for causing disease in plants can be classified into biotic and abiotic factors. Biotic factors are living agents, such as pathogens (including fungi, bacteria, and viruses) that can infect and harm plants, while abiotic factors include non-living elements like environmental conditions (drought, frost, salinity) that can lead to plant stress and susceptibility to diseases. The comprehensive nature of this answer allows for a broader understanding of disease causation in plants, highlighting that both living organisms and environmental conditions play significant roles in plant health and disease dynamics. Each of the other options specifies only a subset of biotic agents or abiotic stressors, rather than encompassing the full range of possibilities that impact plant health.