Cybridization for Plant Improvement
Posted August 2025
Researchers: Ahmad A. Omar, Fred Gmitter, Christine Chase, Mayara Murata, Jim Graham, Flavia Tabay Zambon, Jude Grosser
Contact: Ahmad A. Omar, UF/IFAS CREC omar71@ufl.edu
Summary:
To determine whether cytoplasmic components from canker-resistant ‘Meiwa’ kumquat could improve disease tolerance in grapefruit, we created 144 cybrids via protoplast fusion using ‘Flame’, N11-11 Ruby somaclone, and ‘White Marsh’ grapefruit. All cybrids maintained grapefruit morphology and inherited mitochondrial genomes from ‘Meiwa’. Chloroplast inheritance was biased toward kumquat, with 125 cybrids carrying kumquat chloroplasts and 19 retaining those of grapefruit. Canker tolerance, evaluated through attached leaf assays, remained low in cybrids with grapefruit chloroplasts but was significantly improved in many cybrids with kumquat chloroplasts. The cybrids were field-planted at UF/IFAS IRREC, Fort Pierce, under high disease pressure. Most trees declined due to huanglongbing (HLB) symptoms and herbicide damage, with only a few survivors after two years. These were grafted onto UFR-1 rootstock and moved to a high-salinity commercial grove, where most continued to decline. However, one standout - Cybrid #3, derived from N11-11 and bearing kumquat chloroplasts, remained vigorous and symptom-free for both canker and HLB. Cybrid #3 was propagated onto UFR-5 rootstock. qPCR testing of 19 clones detected no Candidatus Liberibacter asiaticus (CLas) bacteria (Ct = 40), suggesting possible HLB tolerance. A new trial population is under evaluation in Fort Pierce, with growth data collection in progress. Fruiting potential and performance are also being assessed, with topworking underway at UF/IFAS CREC, Lake Alfred, to accelerate testing.
Take Home Message:
- Cybrids with kumquat chloroplasts showed improved canker tolerance compared to those with grapefruit chloroplasts.
- Cybrid #3 exhibited no symptoms of citrus canker or HLB, even under high disease pressure and environmental stress.
- qPCR analysis of Cybrid #3 progeny revealed no CLas infection, suggesting potential HLB tolerance. Validation is underway.
