Examination of the Responses of Different Genotypes of Citrus to Huanglongbing (Citrus Greening) Under Different Conditions

Abstract

Citrus Huanglongbing (HLB) is one of the most devastating diseases of citrus worldwide. The causal agent of HLB in Florida is thought to be 'Candidatus Liberibacter asiaticus'. In this work, we examined the responses of 30 different genotypes of citrus to Florida isolates of 'Ca. L. asiaticus' under controlled conditions in the greenhouse or growth room. Although 'Ca. L. asiaticus' was able to multiply in all of the plants, a wide range of responses was observed among different hosts. Based on the symptoms developed and the ability of plants to continue growth, the different genotypes were grouped into four categories: sensitive, which exhibited severe chlorosis on leaves, greatly reduced growth, and eventual death; moderately tolerant, which exhibited some scattered distinct symptoms but little or no growth reduction and no plant death; tolerant, which exhibited very minimal symptoms; and genotypes, which exhibited variable reactions. Interestingly, although 'Ca. L. asiaticus' was unevenly distributed within each particular plant, comparison of titers of the bacterium in different citrus genotypes revealed that most accumulated similar levels of 'Ca. L. asiaticus', demonstrating that there is no strict correlation between bacterial titer and severity of disease. Incubation of infected plants in the growth room with continuous light greatly affected symptoms production by reducing the time before distinctive symptoms developed and significantly increasing severity of chlorosis of leaves of all citrus genotypes. These results provide additional evidence of the correlation between disruption of phloem translocation of carbohydrates during HLB infection and the appearance of chlorotic symptoms in leaves of infected trees. We also examined interaction between 'Ca. L. asiaticus' and Citrus tristeza virus, which usually occurs in trees that become infected with HLB, and found no synergistic effect of the two pathogens. We trust that observations reported here will provide reagents for further examination of the 'Ca. L. asiaticus'-citrus interaction to advance the understanding of how 'Ca. L. asiaticus' causes disease and to develop methods or trees to overcome the disease.

Amino acids implicated in plantdefenseare higher inCandidatusLiberibacter asiaticus-tolerant citrus varieties

“…11 Similar results were also reported by Sagaram and Burns (2009). 12 In another study, Hajivand et al, (2009) also assessed eighteen 18 Malaysian citrus species for susceptibility to CLas by graft inoculation.…”

Can CRISPR Win the Battle against Huanglongbing?

“…; 3) tolerant, which showed minimal symptoms such as Eureka lemon, Persian lime, Carrizo citrange, and Severinia buxifolia; 4) seven genotypes showed variable symptom. The titers of CLas were not related with the severity of the symptoms [17].…”

Technological Advances in Huanglongbing (HLB) or Citrus Greening Disease Management

“…Based on severity of HLB symptoms and the ability to continue growth of the plants inoculation with 'Ca. L. asiaticus ' Folimonova et al (2009) grouped citrus genotypes into four categories as (i) sensitive: C. halimii, Nules clementine mandarin, Minneola tangelo, sweet oranges and grapefruit (ii) moderately tolerant: Sun Chu Sha mandarin, sour orange, volkamer lemon, C. macrophylla, wingle citrumelo, citron, Palestine sweet lime, acid lime, calamondin, and C. micrantha (iii) tolerant: Eureka lemon, Persian lime, Carrizo citrange, and Severinia buxifolia (iv) variable (some branch sensitive and some branch tolerant): pummelos, C. amblycarpa, cleopatra mandarin, C. indica, and…”