Title: Under severe citrus canker and HLB (Huanglongbing) pressure, Triumph and Jackson perform better than Flame and Marsh grapefruit Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: August 23, 2012
Publication Date: N/A
Technical Abstract: Huanglongbing (HLB) and Citrus Canker (CC) threaten the viability of Florida grapefruit production. Triumph (T), reportedly a grapefruit/sweet orange hybrid, is similar to seedy white grapefruit with earlier maturity and lower bitterness. Jackson (J) is a low-seeded budsport of Triumph. Tree health and productivity of T, J, and standard cultivars Marsh (M) and Flame (F) planted in a replicated field trial were assessed for 3 years, in a site with endemic HLB and CC. In each year overall tree health of T/J was significantly greater than M/F. Severity of CC was significantly less on T/J than on M/F, while foliar HLB symptoms in the fall were similar among cultivars. Titers of Liberibacter asiaticus were assessed by Polymerase chain reaction (PCR) in January 2010 and November 2012: there were no significant differences among cultivars in random leaf samples or most-symptomatic diagnostic samples in the 2010 analyses and in 2012. M/F developed very thin canopies while T/J had normal canopy density. T/J had extensive blotchy mottle characteristic of HLB on leaves year-round while M/F trees appeared to drop severely HLB-symptomatic leaves in the winter. Cumulative numbers of fruit/tree were greater for T/J (255/220) than for M/F (29/66). Tree height of T/J was slightly greater than in M/F. Canopy volume was greater in T/J than M/F in some years, but trunk cross sectional area (TCSA) was not different, and there were no cultivar differences in TCSA increase over the study period. Cumulative percent fruit drop was greater in M/F than T/J (F=50; M=53; T=15; J=14). Fruit quality assessments were made each cropping season. T/J fruit always met commercial maturity standards whereas M/F fruit usually did not due to low total soluble solids and low Brix/acid ratios. In 2011/2012 many M/F were small and/or misshapen while T/J fruit were of normal size and shape. These results suggest that T/J or other grapefruit-like cultivars may be viable alternatives to standard grapefruit cultivars in the presence of severe HLB and CC, with apparent tolerance to HLB in T/J. Furthermore, it provides evidence that useful tolerance to HLB exists within conventional scion genotypes.