Citrus Rootstocks Explained: Disease Tolerance, Tree Health & Yield - Dr. Kim Bowman

In this episode of the Citrus Research International (CRI) Podcast, we speak with Dr Kim Bowman, research geneticist at the US Department of Agriculture – Agricultural Research Service (USDA-ARS) in Fort Pierce, Florida, and one of the world’s leading citrus rootstock breeders.

Dr Bowman shares insights from more than 30 years of citrus rootstock development, including the release of 16 USDA rootstocks, one of which, US-942, has become the most widely planted rootstock in Florida. He explains why rootstocks play a foundational role in citrus production, influencing tree vigour, anchorage, nutrient uptake, disease tolerance and ultimately fruit yield and quality.

The conversation focuses strongly on Huanglongbing (HLB) and how Florida’s experience with the disease reshaped global thinking around rootstocks. Dr Bowman explains how certain rootstocks show improved tolerance by limiting bacterial multiplication in the root system, while also emphasising that tolerance is not immunity. Rootstocks, he notes, are one part of a broader system aimed at sustaining fruit production under disease pressure.

He also unpacks how rootstocks are bred and evaluated, why they cannot simply be “discovered” like scion mutations, and how long-term field performance is essential before release. Additional discussion covers tolerance to phytophthora, nematodes, soil constraints, anchorage under extreme weather, and the role rootstocks may play in future production systems such as protected structures.

For South African growers, the key takeaway is clear: rootstocks are not interchangeable. They are strategic production decisions that shape orchard performance for decades and become even more critical as disease, climate and soil challenges intensify.

About the CRI Podcast

The CRI Podcast features interviews with leading researchers and extension experts from Citrus Research International, highlighting the science and field innovation that keep Southern Africa’s citrus industry competitive and sustainable.