Citrus (Citrus sp.) growers’ selection of a rootstock is a key decision that can affect the profitability and longevity of a grove. Using improved rootstocks can induce traits in a scion that make citrus trees more resilient to pests and diseases and can enhance their horticultural attributes, such as size, yield, and fruit quality (Bowman et al., 2016; Wutscher and Bowman, 1999; Wutscher and Hill, 1995). Since the outbreak of citrus greening or Huanglongbing (HLB), research of rootstocks has gained renewed interest because of the impact they can have on coping with the disease (Castle et al., 2020).
Caused by the bacterium Candidatus Liberibacter asiaticus (CLas) and transmitted by the asian citrus psyllid (Diaphorina citri), HLB is a devastating disease that affects major commercial citrus production areas worldwide. First found in Florida in 2005, HLB spread rapidly throughout the state, where it is now endemic. As a consequence, statewide sweet orange (Citrus sinensis) yield has decreased by 55% and production has decreased by more than 70% (Singerman et al., 2017; U.S. Department of Agriculture, 2019). Hodges et al. (2014) estimated that HLB caused $7.80 billion in economic losses between 2006 and 2013. At the farm level, growers have sustained losses, thus forcing many to exit the industry. From 2002 to 2017, the number of citrus growers in Florida decreased by 4614 (62%) (Singerman and Rogers, 2020; Singerman et al., 2018).
Because there is still no effective treatment or management strategy to cure the disease, it is crucial for growers to optimize grove practices and management. One way to achieve such a goal would be to plant rootstocks that provide enhanced tolerance to the disease, thereby resulting in higher production. However, the results of recent studies of the effect of rootstock on tolerance to HLB in field trials have been inconsistent (Albrecht et al., 2012; Bowman et al., 2016; Stover et al., 2016). According to Bowman et al. (2016), such results are partly attributable to erratic disease spread and development of symptoms. For example, Albrecht et al. (2012) and Stover et al. (2016) showed little or no rootstock effect on growth, HLB symptoms, and CLas titer. However, in some cases, Albrecht et al. (2012) found that older infected trees showed rootstock effects on yield following CLas infection.
This study aimed to provide estimates of the performance of different rootstocks grafted with ‘Valencia’ sweetorange scions in commercial field conditions within an HLB-endemic environment. To the best of our knowledge, these are the first estimates obtained from side-by-side trials that compared the performance of rootstocks developed by two breeding programs in Florida, namely that of the University of Florida and the U.S. Department of Agriculture (USDA). Therefore, those estimates can be particularly useful to growers deciding which rootstocks to plant. Importantly, this analysis evaluated the biological (i.e., yield) and economic (i.e., revenue) performance. Yield was measured as the number of pounds of solids per acre because that unit is the basis on which growers are paid for their crop and is, therefore, key to profitability and sustainability.
Albrecht, U., McCollum, G. & Bowman, K.D. 2012 Influence of rootstock variety on huanglongbing disease development in field-grown sweet orange (Citrus sinensis) trees Scientia Hort. 138 210 220 doi: 10.1016/j.scienta.2012.02.027
Bowman, K.D., McCollum, G. & Albrecht, U. 2016 Performance of ‘Valencia’ orange (Citrus sinensis) on 17 rootstocks in a trial severely affected by huanglongbing Scientia Hort. 201 355 361
Florida Department of Agriculture and Consumer Services 2020 Annual citrus budwood report for 2019-20 2 Feb. 2021. <https://www.fdacs.gov/content/download/94009/file/2019-2020-Annual-Report.pdf>
Florida Department of Citrus 2017 Post price estimate fruit price reports 2 Feb. 2021. <https://app.box.com/embed/s/4905ob93hh/folder/16290589293?showItemFeedActions=true&showParentPath=true>
Florida Department of Citrus 2018 Post price estimate fruit price reports 2 Feb. 2021. <https://app.box.com/embed/s/4905ob93hh/folder/44517869735?showItemFeedActions=true&showParentPath=true>
Florida Department of Citrus 2019 Post price estimate fruit price reports 2 Feb. 2021. <https://app.box.com/embed/s/4905ob93hh/folder/98675291207?showItemFeedActions=true&showParentPath=true>
Florida Department of Citrus 2020 Post price estimate fruit price reports 2 Feb. 2021. <https://app.box.com/embed/s/4905ob93hh/folder/98675291207?showItemFeedActions=true&showParentPath=true>
Hodges, A.W., Rahmani, M., Stevens, T.J. & Spreen, T.H. 2014 Economic impacts of the Florida citrus industry in 2012–13 2 Feb. 2021. <http://www.fred.ifas.ufl.edu/pdf/economic-impactanalysis/Economic_Impacts_Florida_Citrus_Industry_2012-13.pdf>
Singerman, A 2020 How much can Florida growers afford to spend on caretaking processed orange groves? 3 Mar. 2021. <https://citrusindustry.net/2019/12/23/how-much-can-florida-growers-afford-to-spend-on-caretaking-processed-orangegroves/>
Singerman, A. & Rogers, M.E. 2020 The economic challenges of dealing with citrus greening: The case of Florida J. Integr. Pest Manag. 11 1 1 7
Singerman, A., Lence, S.H. & Useche, P. 2017 Is area-wide pest management useful? The case of citrus greening Appl. Econ. Perspect. Policy 39 4 609 634
Stover, E., Inch, S., Richardson, M.L. & Hall, D.G. 2016 Conventional citrus of some scion/rootstock combinations show field tolerance under high huanglongbing disease pressure HortScience 51 2 127 132