Relation between plant nutrition, hormones, insecticide applications, bacterial endophytes, and Candidatus Liberibacter Ct values in citrus trees infected with Huanglongbing

Abstract

Intensive insecticide and nutrient management have been attempted worldwide to reduce citrus huanglongbing (HLB) symptom development and yield loss. However, effects of insecticide and nutrient applications on HLB have been poorly understood. Leaf nutrients, jasmonic and salicylic acid contents, cycle threshold (Ct) values of Ca. Liberibacter asiaticus (Las), and community structure of endophytic α-proteobacteria were evaluated after insecticide treatment, 'nutrition' treatment (including systemic resistance inducing agents), or both in comparison with a control in a two-factor field experiment in 2008-2012. Leaf N, Mn, Zn and B significantly increased whilst Cu decreased after nutrient applications. Salicylic acid significantly increased in old leaves treated with insecticides, nutrients or both, and in young leaves treated with nutrients only. The jasmonic acid concentration was highest after the nutrition treatment in both old and young leaves. Ct values of Las and leaf area and weight significantly increased after long-term nutrient applications in 2011 and/or 2012. Redundancy analysis of the endophytic α-proteobacteria community structure indicated that the communities were mainly separated according to nutrient applications, which were positively associated with Ct values of Las and Ca, Mn, Zn, B, Mg, and Fe contents in leaf samples collected in 2012. Thus, effects of insecticides on HLB were significant in the early 2-year period whilst nutrients had significant effects on Las content and leaf size and weight after at least 3 years of application.

Costs and benefits of insecticide and foliar nutrient applications to huanglongbing‐infected citrus trees

“…Phloem‐feeding insects such as ACP introduce salivary secretions with effector molecules that can influence defense signaling, host development and symptoms of pathogens they vector . Insecticide and foliar nutrition influence leaf nutrition status in different ways . Understanding these interactions requires much more work.…”

“…Leaf nitrogen was significantly higher in these trees from 2008 to 2012 after nutrition and lower after insecticide applications. 49 Citrus trees are efficient absorbers of foliar nutrient sprays, and leaf nitrogen levels increase more quickly in response to foliar than to soil application. 50 Young leaves absorb more nitrogen than older, hardened leaves.…”

“…57 Insecticide and foliar nutrition influence leaf nutrition status in different ways. 49 Understanding these interactions requires much more work.…”

Infection Density Dynamics of the Citrus Greening Bacterium “Candidatus Liberibacter asiaticus” in Field Populations of the Psyllid Diaphorina citri and Its Relevance to the Efficiency of Pathogen Transmission to Citrus Plants

“…Liberibacter asiaticus" is noncultivable (6), most recent studies have adopted culture-independent approaches using conventional PCR and/or quantitative PCR techniques for the detection and quantification of "Ca. Liberibacter asiaticus" not only in citrus plants (15,(18)(19)(20)(21)(22)(23)(24)(25) but also in D. citri (9,13,(15)(16)(17)(18). Meanwhile, the biological relevance and consequence of the infection density of "Ca.…”

Filosfera de citros sob manejo convencional e ecológico: estrutura da comunidade bacteriana e monitoramento de cobre

“…As enfermidades cancro cítrico, clorose variegada, morte súbita, "pinta preta" são as principais responsáveis pelas perdas nas regiões dos Estados de São Paulo, Bahia, Minas Gerais e Paraná (Barbosa et al, 2014). O outro importante problema para a cultura do citros é o inseto psilídio (Diaphorina citri), o qual é vetor da bactéria causadora de HLB ou "greening", a principal doença que afeta a citricultura (Shen et al, 2013). Candidatus…”