What is a significant effect of inadequate airflow in a greenhouse?

Inadequate airflow in a greenhouse can lead to a higher risk of fungal diseases, which significantly affects plant health. Proper airflow helps to regulate humidity levels and prevent the excessive moisture that fosters a conducive environment for fungal spores to thrive. When airflow is insufficient, humidity can build up, creating conditions that are perfect for diseases such as powdery mildew or botrytis. Plants in such environments are more susceptible to these pathogens, which can lead to serious health issues for the crops and reduce overall yield.

The other choices reflect conditions that are positively or negligibly affected by airflow rather than negatively impacted by its inadequacy. For instance, increased light penetration is a result of proper greenhouse design and canopy management, not airflow. Reduced heat retention is generally more associated with greenhouse design and insulation than airflow deficiencies. Enhanced plant growth typically requires optimal conditions, including adequate airflow—not the opposite. Therefore, the correct answer emphasizes the detrimental effect that poor airflow can have on disease prevalence in greenhouse environments.