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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Subtropical Insects and Horticulture Research » Research » Publications at this Location » Publication #318768
Title: An HLB-tolerant citrus rootstock: What exactly does that mean?

Author
item CASTLE, B - University Of Florida
item GROSSER, J - University Of Florida
item Bowman, Kim
item Stover, Eddie

Submitted to: Citrus Industry
Publication Type: Trade Journal
Publication Acceptance Date: 5/16/2015
Publication Date: 6/1/2015
Citation: Castle, B., Grosser, J., Bowman, K.D., Stover, E.W. 2015. An HLB-tolerant citrus rootstock: What exactly does that mean? Citrus Industry, June 2015: 16-19.

Interpretive Summary:

Technical Abstract: The article summarizes results from several rootstock trials and attempts to answer the question, “So what exactly is an HLB (huanglongbing)-tolerant rootstock”? Apparently healthy trees are often observed in blocks otherwise decimated by huanglongbing. There are likely any number of possible explanations for such trees including the genetics of the scion and rootstock and their interaction, site and cultural factors and complex interactions between trees, the Asian citrus psyllid (ACP) vector and the presumed huanglongbing pathogen that may also be related to variability in the bacterium itself. Furthermore, one must be aware of the role of randomness that results in some “lucky” trees, even when an epidemic is quite advanced. It would be easy to identify a rootstock that appeared to confer tolerance, but so far there is no clear evidence that such a rootstock exists. Currently, labeling a rootstock as huanglongbing tolerant could be misleading because doing so may lead to certain unproven expectations. Our field observations clearly show that trees on virtually any rootstock are not uniformly affected by huanglongbing and trees on standard rootstocks such as Swingle and Carrizo are not always among the poorest performers. There are plenty of instances where trees on the same rootstock in a trial display a mixture of huanglongbing symptoms; some trees appear to endure huanglongbing while others are badly affected. What is the expectation if an apparently surviving tree in a trial or ones found in commercial groves are propagated and then used as the rootstock for new plantings? Would all such trees show tolerance to huanglongbing or would the outcome be the same, i.e., some trees endure while others succumb? Therefore, until we understand more about huanglongbing and rootstocks, it is best to keep in mind that some combination of at least three components may be involved in rootstock reactions to huanglongbing. They are the proportion of trees that become affected by huanglongbing after a certain time, the proportion of trees that show visible symptoms of huanglongbing and the severity of huanglongbing symptoms after infection. Ongoing and additional studies are necessary to verify huanglongbing-tolerant rootstocks that confer real economic advantages in the context of commercial Florida citrus production.