HORTSCIENCE 55(1):40–45. 2020. https://doi.org/10.21273/HORTSCI14585-19 and increase iron and ammonium availability. In the southeastern United States, pine bark is Vaccinium arboreum the common soil amendment used to increase Impacts of soil organic matter and is typically incorpo- rated into the top soil layer (Williamson Rootstocks on Vegetative Growth and et al., 2018). Without soil amendments, blueberry growth and yields decrease, and Yield in Two Southern Highbush plants become chlorotic and nonproductive. However, soil amendments required for es- tablishment and maintenance of blueberry Blueberry Cultivars plantings are costly (Julian et al., 2012) and Rebecca L. Darnell and Jeffrey G. Williamson may not be sustainable in the long term. Horticultural Sciences Department, University of Florida, Gainesville, FL Vaccinium arboreum is a wild blueberry native to the southeastern United States. It is a 32611 single-trunk, small tree that is adapted to low- Deanna C. Bayo and Philip F. Harmon organic matter mineral soils. Furthermore, this species tolerates soil pH up to 6.5 and—contrary Plant Pathology Department, University of Florida, Gainesville, FL 32611 to cultivated Vaccinium—can assimilate nitro- Additional index words. bacterial leaf scorch, fruit quality, grafting, sparkleberry, Vaccinium gen in the nitrate form (Darnell and Hiss, 2006), corymbosum, interspecific hybrid which is the predominant nitrogen form at higher pH. Because of the broader soil adapta- Abstract. Vaccinium arboreum Marsh is a small tree adapted to low-organic matter soils tion of V. arboreum compared with cultivated and is one of the few ericaceous species that tolerates soil pH greater than 6.0. It has a Vaccinium species, studies have examined the deep root system and is more drought tolerant than cultivated blueberry. The use of V. use of V. arboreum as a rootstock to increase arboreum as a rootstock for commercial blueberry production has been studied soil adaptability of commercial blueberry pro- previously in young blueberry plantings. The objective of the current study was to duction. Ballington (1996, 1998) found that expand on earlier work and evaluate growth, productivity, and tolerance to bacterial leaf grafting rabbiteye blueberry (V. virgatum)onto scorch (Xylella fastidiosa) in established plantings of own-rooted vs. grafted southern V. arboreum rootstocks increased plant growth highbush blueberry (SHB). Two field plantings of grafted and own-rooted ‘Meadowlark’ and yield compared with own-rooted plants. and ‘Farthing’ SHB were established in May 2011: one at the University of Florida– More recently, Casamali et al. (2016) reported Institute of Food and Agricultural Sciences (UF-IFAS) Plant Science Research and that SHB (V. corymbosum interspecific hybrid) Education Unit in Citra, FL, and the other at a commercial blueberry farm in Archer, grafted onto V. arboreum had increased yields FL. At both sites, four rootstock–scion combinations were grown in either pine bark- compared with own-rooted plants when grown amended or nonamended soil. Canopy volume was greater in grafted compared with on nonamended soil, and similar yields com- own-rooted ‘Meadowlark’ at both locations throughout the 4 years of the study (2015– pared with own-rooted plants on amended soil 18), whereas canopy volume in ‘Farthing’ was not consistently different. For both during the first 2 years of production. Thus, the cultivars and both locations, canopy volume was greater on amended compared with use of V. arboreum as a rootstock for grafted nonamended soil. Although canopy growth was not consistently increased in the grafted SHB cultivars has the potential to decrease the compared with own-rooted plants, yield was greater in grafted plants of both cultivars at use of pine bark (or other soil amendments) both locations. Cumulative yield over the 4 years was similar between grafted plants needed for optimal blueberry production, ex- grown on both amended and nonamended soil, and was significantly greater than yield of pand production areas to different soil types, and own-rooted plants on nonamended soil, suggesting the use of this rootstock may decrease increase sustainability. the requirement for pine bark amendment. In general, grafted plants produced larger Although results from short-term research berries, with no negative impacts on fruit soluble solids, titratable acidity, or firmness. trials indicate the potential of using V. arbor- ‘Meadowlark’—an SHB cultivar that exhibits high sensitivity to bacterial leaf scorch— eum as a rootstock for blueberry, data from displayed decreased development of bacterial leaf scorch symptoms when grafted onto V. longer term trials are still needed. The current arboreum compared with own-rooted plants. These results indicate the potential benefits research continues the work initiated by Casa- of grafting SHB onto V. arboreum rootstock, particularly under marginal soil conditions. mali et al. (2016) and examines the use of V. However, a complete economic analysis that also takes into account any differences in arboreum as a rootstock for SHB during 4 longevity between the two systems must be done to determine whether the benefits of years after the establishment period. The using grafting are feasible financially for the grower. hypothesis tested in the current research is that SHB grafted onto V. arboreum rootstocks have increased growth and yield compared Rootstocks are commonly used in tree blackberry, raspberry, and blueberry) has with own-rooted SHB in both pine bark- fruit production and, more recently, vegeta- not been commonly adopted. Rootstocks amended and nonamended soils. The objec- ble production systems (Djidonou et al., offer many advantages to crops, including tives were to evaluate the effects of soil 2017; Zhao et al., 2018). However, the use size control (Basile and DeJong, 2018), in- treatment (amended vs. nonamended) and root of rootstocks in berry crops (strawberry, creased yields (Xu et al., 2014), increased system (own-rooted vs. grafted onto V. arbor- tolerance to biotic and abiotic stress (Liu eum) on canopy growth, yield, berry weight, et al., 2014), and enhanced soil adaptation and berry quality in two cultivars of SHB. In (Penella et al., 2015). addition, during the course of the experiment, Received for publication 23 Sept. 2019. Accepted Cultivated blueberry (Vaccinium species) root system differences in susceptibility to for publication 21 Oct. 2019. have strict soil requirements for optimum bacterial leaf scorch (Xylella fastidiosa)were Published online 12 December 2019. growth. These include low pH (4.0–5.5), high observed; thus, incidence and severity of this This material is based on work supported by the organic matter, good aeration and drainage disease were also evaluated. Florida Department of Agriculture and Consumer (Williamson et al., 2018), and readily avail- Services (Award 024045). able iron and ammonium (Darnell and Hiss, R.L.D. is the corresponding author. E-mail: rld@ Materials and Methods ufl.edu. 2006; Nunez et al., 2015). As a result of these This is an open access article distributed under the requirements, soil amendments and other Two field plantings of grafted and own- CC BY-NC-ND license (https://creativecommons. modifications (e.g., sulfur applications) are rooted ‘Meadowlark’ and ‘Farthing’ SHB org/licenses/by-nc-nd/4.0/). used to increase organic matter, lower pH, were established in May 2011: one at the 40 HORTSCIENCE VOL. 55(1) JANUARY 2020 UF-IFAS Plant Science Research and Edu- further data were available from that loca- Bacterial leaf scorch symptoms were cation Unit in Citra, FL, and the other at a tion. Canopy volume was determined by quantified in ‘Meadowlark’ experimental commercial blueberry farm (Straughn Farms measuring plant height and plant diameter plots in Citra five times between Aug. 2016 LLC, Archer, FL). These cultivars have high in two directions. Because of cultivar differ- and Nov. 2018. Data were acquired on yield potential (Williamson et al., 2014) and ences in canopy shape, a half-ellipsoid equa- ‘Meadowlark’ only, because that cultivar were widely planted by the industry at the tion, Eq. [1], was used to estimate canopy exhibits high sensitivity to the disease. Dis- initiation of this project. At each site, four volume in ‘Farthing’ and an elliptic cylinder ease incidence was recorded as a percentage scion–root system combinations were grown equation, Eq. [2], was used to estimate of the live plants per plot that had two or more (‘Meadowlark’ and ‘Farthing’ on their own volume in ‘Meadowlark’. leaves showing characteristic marginal roots or grafted onto V. arboreum). Details on scorch. Disease severity was quantified visu- the propagation, grafting, and sources of V. Canopy volume ʻFarthingʼ ally on a 0% to 100% scale for each of the arboreum rootstocks are given in Casamali three most symptomatic living plants per =2=3 ·p·Height et al. (2016). Plants were spaced 0.9 m in the plot. For symptoms to be considered caused row, with 3 m between rows at the Citra · ½ Diameter 1 · ½ Diameter 2 [1] by bacterial leaf scorch, and therefore quan- location; and 0.9 m in the row, with 3.3 m tified, yellow, defoliated stems and dieback between rows at the Archer location. At both Canopy volume ʻMeadowlarkʼ had to be associated with leaf scorch and not locations, the soil is Arrendondo sand, pH = p·Height · ½ Diameter 1 a result of abiotic factors or fungal diseases. 6.0, and organic matter 1.4%. Each In addition, before symptom ratings, the · scion–root system combination was grown in ½ Diameter 2 [2] presence of X. fastidiosa in symptomatic either pine bark-amended or nonamended leaves and stems was confirmed via real- soil. The amended treatment consisted of soil Fruit yield and mean berry weight at both time polymerase chain reaction at the Uni- amended by incorporating a 10-cm layer of locations were determined throughout the versity of Florida Plant Diagnostic Center, pine bark into the top 20 cm of soil, whereas harvestperiodeachyear.Berrieswerehand- Gainesville, FL. Incidence data were ana- the nonamended soil did not have any soil harvested two to three times per week, lyzed using PROC NPAR1WAY in SAS 9.4 amendments incorporated.