Skip to main content
ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Subtropical Insects and Horticulture Research » Research » Publications at this Location » Publication #423657
Research Project: Genetic Improvement of Citrus for Superior Production, Marketability, and Tolerance to Huanglongbing

Location: Subtropical Insects and Horticulture Research

Title: Nursery characteristics and field performance of nine novel citrus rootstocks under HLB-endemic conditions

Author
item TARDIVO, CAROLINE - University Of Florida
item Patel, Sailindra
item Bowman, Kim
item ALBRECHT, UTE - University Of Florida

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2025
Publication Date: 5/16/2025
Citation: Tardivo, C., Patel, S.K., Bowman, K.D., Albrecht, U. Nursery characteristics and field performance of nine novel citrus rootstocks under HLB-endemic conditions. HortScience. 60(6):931-939. 2025. https://doi.org/10.21273/HORTSCI18529-25.
DOI: https://doi.org/10.21273/HORTSCI18529-25

Interpretive Summary: The devastating effects of the bacterial disease Huanglongbing have negatively impacted the Florida citrus industry for almost two decades, with limited genetic tolerance or resistance among commercially relevant scion cultivars. The rootstock is known to significantly influence tree tolerance to the disease, and there is an urgency to identify rootstock cultivars that impart tolerance along with superior horticultural traits to the grafted scion. This study evaluates nine novel USDA citrus rootstocks for their field performance to identify those that most enhance yield, fruit quality, and disease tolerance under HLB-endemic growing conditions. In addition, the rootstocks were evaluated regarding the most suitable method for uniform nursery propagation, whether by seed or vegetative methods. One of the rootstocks, released by USDA as 'US SuperSour 4' exhibited outstanding field performance as compared with the other rootstocks and the commercial standards. SuperSour 4 cannot be propagated uniformly by seed and must be propagated by cuttings or tissue culture. The study also provided extensive information critical for continuing research about field performance traits of hybrid progeny and the use of molecular markers as fingerprints for clonal rootstocks and their seedlings.

Technical Abstract: The devastating effects of the bacterial disease Huanglongbing (HLB) have negatively impacted the Florida citrus industry for almost two decades, with limited genetic tolerance or resistance among commercially relevant scion cultivars. The rootstock is known to significantly influence tree tolerance to HLB, and there is an urgency to identify rootstock cultivars that impart tolerance along with superior horticultural traits to the grafted scion. This study evaluates nine novel citrus rootstocks for their field performance to identify those that most enhance yield, fruit quality, and disease tolerance under HLB-endemic growing conditions. In addition, the rootstocks were evaluated regarding their nursery characteristics, particularly their ability to produce genetically uniform (true-to type) progeny by nucellar polyembryony. The genetic uniformity was assessed by morphological characterization of seedlings and molecular analysis using single sequence repeat (SSR) markers. The visual identification of true-to-type progeny was hampered by limited morphological distinction for cultivars exhibiting a unifoliate leaf trait and varying leaf morphology for those exhibiting a trifoliolate trait. SSR marker analysis showed that six of the nine novel rootstocks produced exclusively zygotic seedlings and would need to be propagated by vegetative methods for commercial distribution. Three rootstocks, US-1680, US-1687, and US-2111 produced true-to-type (nucellar) seedlings with a frequency of 25-58%, suggesting some potential for seed propagation. Field performance of the nine rootstocks was evaluated in a trial with 'Valencia' (Citrus sinensis) scion. Two additional rootstocks, sour orange, and Swingle were included as rootstock standards. In the field study, US-1688, a hybrid of C. maxima ‘Hirado’ and C. reticulata 'Cleopatra', induced the highest yield and US-2132, a hybrid of ‘Hirado’ and US-942 (C. reticulata ‘Sunki’ × Poncirus trifoliata ‘Flying Dragon’) induced the best juice quality during the 2022-2023 production season. US-1688 was recently released by the U.S. Department of Agriculture as US SuperSour 4, and the results from this study validate its good performance under HLB-endemic conditions. This study provides comprehensive insights regarding the potential of nine novel rootstocks and similar hybrid progeny to meet the current challenges faced by the citrus industry.