- HUANGLONGBING: DEVASTATING DISEASE OF CITRUS 345
ultimate evaluation will be in the field where they will be exposed to
repeated natural infection by the insect vector.
Genetic improvement of citrus is challenging for a number of reasons,
including the distinctive reproductive biology of the genus, long juve-
nile phase, and requirement for lengthy orchard trials to determine the
performance of new selections. In addition, markets demand fruit with
known and valued characteristics. To achieve new cultivars that are not
susceptible to HLB and have fruit characteristics expected by the con-
sumer may not be possible before the Florida citrus industry has been
permanently downsized.
V. HLB EFFECTS ON FLAVOR AND POSTHARVEST QUALITY
A. Implications of HLB Impacts on Fruit and Juice Quality
The citrus greening disease, or HLB, is not only detrimental to the
health and productivity of citrus trees, but also has an effect on fruit and
juice flavor quality. Unfortunately, this disease hits the citrus industry
on the front and back ends; that is, the disease affects both the ability to
produce fruit and the ability to market the final fruit or juice product.
Most studies have been done on oranges and for purposes of analyses
have been conducted dividing oranges into fruit that are symptomatic
or asymptomatic for HLB (Baldwin et al. 2010; Plotto et al. 2010).
Visually, asymptomatic CLas-positive fruit are similar in appearance
to healthy (CLas-negative) fruit while symptomatic CLas-positive fruit
are commercially undesirable being smaller, greener, asymmetrical,
and having aborted seeds. These fruit are graded out at packing houses
and processing plants for the most part. The problem is that all the
fruit are getting smaller and greener in areas where HLB is prevalent,
thus, asymptomatic fruit are decreasing and symptomatic fruit are
increasing.
Florida is especially impacted by HLB and has experienced a yield
reduction from around 244 million boxes at its high point, down to 74
million boxes estimated for the 2015–2016 season (USDA, NASS 2015).
Much of this is attributed to reduced fruit size and increased prehar-
vest fruit drop discussed elsewhere in this chapter. Since around 90%
of the citrus fruit grown in Florida is juiced and the rest sold as fresh
fruit, there is concern that packing houses and especially the processing
plants will shut down, resulting in a loss of infrastructure that is hard
to replace, even if the disease is eventually controlled. Actually, this
has been happening over the last 10 years with closure of the smaller
packinghouse and processing plant operations.