Re-occurrence of Asiatic citrus canker in the Makkah Province of Saudi Arabia and characterization of the causal agent Xanthomonas citri pv. citri isolated from Mexican lime

Abstract

Asiatic citrus canker (ACC) caused by Xanthomonas citri pv. citri (Xcc) is a destructive disease of citrus crops, worldwide. Typical ACC symptoms were observed on Mexican lime trees in the Makkah Province, Saudi Arabia, where the disease had been thought to be eradicated after its first occurrence in the late 1980ies. It was postulated that insufficient uprooting and burning of infected as well as neighboring symptomless trees proved to have been insufficient. This study aimed to 1) investigate the characteristics of ACC lesions and characterize the pathogen (s) associated with Mexican lime symptoms in the Makkah Province to facilitate early and effective detection, and eventual control, 2) characterize the strain of Xcc involved in the newly observed infections and 3) determine the extent of the disease in the province (incidence and severity). ACC was found to be widespread, with an average incidence of 80% in Al-Jumum and 100% in Khulays regions, and severity ranged from 10 to 40%. The identity of the ACC causal agent was confirmed by multiplex real-time PCR and CRISPR typing (cas1 gene) as Xcc. Using CRISPR typing, six strains were identified as spoligotype 10 (A* lineage 4.2), determined on Saudi strains isolated in the 1980s. One strain was identified as a new spoligotype (Makkah 7), most closely related to spoligotype 9 (A* lineage 4.1). Based on our results, it appears that the Xcc variants that occur in the regions Al-Jumum and Khulays have a similar host range to that of Xcc-A*. This confirms the larger geographical distribution of pathotype A*, and this is the second outbreak of ACC in the Makkah Province after some 20 years of supposed absence. The recent rediscovery of ACC-infected trees of Mexican lime in Makkah Province indicates the need for a more frequent survey schedule and a strict tree removal program for better control of ACC.