Of all citrus diseases HLB is often described as the most destructive and lethal (Bove 2006; Bove and Ayres 2007; Gottwald et al. 2007). Bove (2006) reports that “HLB symptoms are virtually the same wherever the disease occurs. Infected trees show a blotchy mottle condition of the leaves that results in the development of yellow shoots, the early and very characteristic symptom of the disease. Trees are stunted, declining and bear a few, small-sized, and deformed (lop-sided) fruits, that are poorly coloured (greening) and with coloration starting at the peduncular end (colour inversion).” The taste of the fruit is also affected. David Hall, an entomologist with USDA in Fort Pierce, Florida describes the taste as “jet fuel mixed with Vicks VapoRub” (Stokstad 2006).
Kim et al. (2008) analyzed citrus response to HLB infection. Microarray analysis of citrus revealed that infection affected the expression of 624 genes including those involved with sugar metabolism, plant defense, phytohormone and cell wall metabolism. Anatomical analyses showed that HLB infection caused phloem disruption, sucrose accumulation, and plugged sieve pores. Phloem disruption and blockage is likely to be caused by host responses rather than by HLB bacterial aggregations. Plugged sieve pores and upregulation of genes involved in sucrose biosynthesis is thought to cause accumulation of sucrose in leaves leading to nutrient deficiencies in sink organs, stunting of plant growth, fruit maturation and seed development (Kim et al. 2008).
HLB affects almost all citrus cultivars, and causes substantial economic losses to the citrus industry by shortening the lifespan of trees and making fruit inedible (Das et al. 2007). Gottwald et al. (2007) report that “almost 100 million trees have been affected and destroyed in many countries of South and Southeast Asia, Indonesia, Philippines, India, Arabian Peninsula, and South Africa, compromising the local citriculture (Aubert et al. 1985; Bove 1986; Halbert and Manjunath 2004; Toorawa 1998). Since 2004, more than 500 thousand trees were officially eliminated in Brazil due to HLB and it is estimated that an additional 300 to 400 thousand trees were unofficially eliminated by commercial citrus growers.”
No Impact information recorded for Candidatus Liberibacter americanus