Which of the following practices can help mitigate the spread of clubroot in agricultural systems?

Using resistant varieties is a highly effective practice for mitigating the spread of clubroot, a soil-borne disease caused by the pathogen Plasmodiophora brassicae. When resistant varieties are planted, the plants have inherent genetic traits that provide them with the ability to withstand or minimize the effects of the pathogen. This resistance can significantly reduce infection rates and the development of the disease in crops, thereby enhancing overall plant health and yield.

Additionally, utilizing resistant varieties can decrease the amount of pathogen spores in the soil over time, contributing to long-term management of clubroot in agricultural systems. This approach is crucial for sustainable agriculture, as it allows farmers to maintain crop production while minimizing the need for chemical controls that could potentially harm the environment.

In contrast, practices like frequent tillage, over-application of fertilizers, and high-density planting can create conditions that either promote the spread of clubroot or do not address the root cause of the disease. Thus, incorporating resistant varieties stands out as an effective and targeted strategy against clubroot.