Final answer:
The primary cause of sealant retention failure is the sealant's inability to prevent pathogen entry, which can lead to plant infections and hinder healing.
Step-by-step explanation:
The primary cause of failure of sealant retention in plants is often due to the inability of the sealant to adequately prevent pathogens from entering cuts on the plants. When a plant is wounded, it is susceptible to infection by various pathogens. A sealant may stop evaporation, which would otherwise promote healing, but if it fails to create a thorough barrier against pathogens, the plant can become infected.
In contrast, when a sealant is effective, it not only stops evaporation but also protects the wound from pathogens that could cause disease or decay. The use of a proper sealant can lead to successful healing, as evidenced by plants growing new branches after their cuts have been properly sealed. The plants with unsealed cuts, however, are left vulnerable to infection and may not recover as successfully.