Mixed Infections of Ca. Liberibacter asiaticus and Citrus Tristeza Virus Affecting Calamansi (Citrofortunella microcarpa Bunge) in Oriental Mindoro, Philippines

Abstract

Huanglongbing (HLB) and tristeza are the most destructive diseases affecting citrus crops worldwide, including calamansi (Citrofortunella microcarpa Bunge Wijnands) in the Philippines. Oriental Mindoro is the largest calamansi-producing province contributing to about 33% of the country’s production. This study was conducted to determine the current status of the occurrence of HLB and tristeza diseases affecting calamansi in the province through visual observation of symptoms in field surveys and detection of the causal pathogen. Both HLB and tristeza were found in all the nine villages surveyed located in the municipalities of Naujan, Pola, Roxas, and Victoria. Plants were showing the HLB symptom of blotchy mottle accompanied by interveinal chlorosis similar to zinc deficiency, defoliation, and twig die-back. Leaves were small, narrow, thick, and corky with enlarged veins and erect in appearance. Among the total of 155 plants tested from the surveyed farms, 150 were positive for HLB disease. Polymerase chain reaction using the LAS606F and LSSR primer pair that amplifies a 500 bp fragment of the Candidatus Liberibacter asiaticus 16S rDNA has detected the HLB causal pathogen in symptomatic samples with blotchy mottle. Likewise, 154 out of 155 plants were also positive for tristeza by enzyme-linked immunosorbent assay. HLB and tristeza occurred mostly in mixed infections in seven farms while 83% and 90% in the other sites. HLB symptoms appeared to be dominantly expressed.