Evaluation of the tolerance of newly developed citrus cultivars, on different rootstocks, to Huanglongbing

Evaluation of the tolerance of newly developed citrus cultivars, on different rootstocks, to Huanglongbing

Report Date: 04/09/2020
Project: 19-015   Year: 2020
Category: Plant Improvement
Author: Nabil Killiny
Sponsor: Citrus Research and Development Foundation

The first evaluations have been completed with citrus plants we already had on hand which were received from Dr. Grosser in 2018-19. We evaluated new citrus hybrids for their potential use as windbreaks and trap plants. These hybrids were produced from the cross of C2-5-12 Pummelo [Citrus maxima (L.) Osbeck] x pollen from Citrus latipes. Seeds were germinated in calcareous alkaline (pH 8) clay soil supplemented with Phytophthora nicotiana and P. palmivora as a preliminary screen. Three vigorously growing putative hybrid seedlings were selected based on leaf morphology and seedling vigor. Hybrids were verified by Simple Sequence Repeat (SSR) markers, and exhibited a compact and upright tree architecture as seen in the pollen parent (C. latipes). Volatiles extracts showed that hybrid II contained higher amounts of volatiles compared with other hybrids, and was more attractive to D. citri than the other hybrids and its parents. Likewise, the levels of most of released volatiles in hybrid II were higher than those released from the other hybrids. The leaf morphology, seedling potency, and compact and upright architecture of hybrid II suggest that it could be a successful windbreak, whereas its attractiveness to D. citri indicated that it might also act as a trap plant. Planting hybrid II as a windbreak at the edges of citrus orchards could help attract D. citri, and allow focused insecticide applications, thus killing D. citri before reaching the commercial citrus trees. Further experiments have been established in our greenhouse: 1)         Cuttings of “Lucky” (Sugar Belle x Nava Osceola) are well established and were ready to begin sampling of the Spring flush, but has been delayed due to Covid-19 CREC closure.2)         Seeds of seven new rootstocks (UFR 1, 2, 4, 5, 6, 15, and 17) were planted in our greenhouse, germinated, and are now about three months old. These were received from Drs. Grosser and Gmitter. 3)         Scion grafts – we side-grafted five new scions onto UFR-2 in November and mid-December 2019. The six scions include C2-2-1, OLL-8, N-40-6-3, RBB-7-34, Grapefruit 914, and 46 x 20. Some of these need to be re-grafted with new budwood. When the new rootstocks/scions are well established, we can begin challenging the new varieties with D. citri to evaluate their attraction/tolerance to psyllids and HLB. Following the psyllid biology experiments, leaf samples can be taken for metabolite and VOC analyses, perhaps in the next 6-12 months.    


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