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First Report of a New Jojoba (Simmondsia chinensis) Witches’-Broom Disease in Saudi Arabia and its Association With Infection by a ‘Candidatus Phytoplasma australasiae’-Related Phytoplasma Strain

    Affiliations
    Authors and Affiliations
    • A. F. Omar , Department of Plant Production and Protection, College of Agriculture and Veterinary Medicine, Qassim University, 51452, Burydah, Kingdom of Saudi Arabia; and Department of Plant Pathology, Plant Pathology and Biotechnology Laboratory, Faculty of Agriculture, Kafrelsheikh University, 33516 Kafrelsheikh, Egypt
    • E. Pérez-López , Department of Entomology and Plant Pathology, Auburn University, Auburn, AL 36849
    • K. M. Al-Jamhan , Department of Plant Production and Protection, College of Agriculture and Veterinary Medicine, Qassim University, 51452, Burydah, Kingdom of Saudi Arabia
    • T. J. Dumonceaux , Agriculture and Agri-Food Canada, Saskatoon Research Centre, Saskatoon, Saskatchewan, Canada; and Department of Veterinary Microbiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.

      Jojoba (Simmondsia chinensis) is a long-lived perennial evergreen shrub that grows wild in the semiarid region of the Sonora desert in northern Mexico and southwestern U.S.A. Jojoba’s resistance to drought allowed its introduction to Saudi Arabia as a potential desert shrub and a potential source of natural oil used in the cosmetic industry (Al-Soqeer 2014). During a survey conducted in 2016, jojoba plants exhibiting symptoms of witches’-broom and small leaves were observed in the Qassim University experimental farm in Qassim Province, Saudi Arabia. Since the symptoms were indicative of possible infection by phytoplasma, molecular diagnostic assays for phytoplasma detection were employed. Total DNA was extracted from leaf samples of three symptomatic plants and used as template in nested PCR using primer pair P1/P7 followed by R16F2n/R16R2 (Lee et al. 1998 and references therein). A 1.2-kb amplicon was amplified from DNA samples of two symptomatic plants. No amplicons were generated from two asymptomatic plants analyzed. The amplicons generated from symptomatic plants were cloned and the 1.2-kb fragment encompassing the full F2nR2 segment of the 16S rRNA-encoding gene was sequenced. The 16S rRNA-encoding sequences obtained from the two positive samples were mutually identical in common regions and possessed a conserved block (5′-CAAGACGATGATGTGTAGCTGGACT-3′) that is characteristic of ‘Candidatus Phytoplasma’ species (5′-CAAGAYBATKATGTKTAGCYGGDCT-3′), confirming that phytoplasma infection occurred in the Qassim University experimental farm in jojoba plants. To our knowledge, this is the first report of a phytoplasma jojoba witches’-broom (JoWb) disease worldwide. The phytoplasma was designated as JoWb1. The 16S rRNA-encoding DNA sequences of the two JoWb1 strains were deposited to GenBank (KY581663 and KY581664). RFLP analysis of the F2nR2 sequences using iPhyClassifier (Zhao et al. 2009) revealed that JoWb1 is closely related to the reference strain of ‘Ca. P. australasiae’, with a similarity coefficient (F) of 1.00 compared with the reference RFLP pattern of subgroup 16SrII-D (Y10097). We also determined the sequence of the chaperonin-60 (cpn60) universal target (KY704478 and KY704479) from symptomatic samples (Dumonceaux et al. 2014). The cpn60 universal target sequences were identical to one another and shared 99.5% identity with that of peanut witches-broom phytoplasma NTU2011 (NZ_AMWZ00000000). Phylogenetic analysis of these sequences placed them in a clade with the peanut witches’-broom phytoplasma (16SrII). Prior to this study, ‘Ca. P. australasiae’ had never been associated with jojoba plants worldwide, although ‘Ca. P. australasiae’-related strains have been previously reported in ornamental and vegetable plants in the Qassim region of Saudi Arabia (Omar 2017). Results from the present study indicate that the phytoplasma has spread to a new host, highlighting the need for surveillance for this phytoplasma in Qassim region, one of the main agricultural areas in Saudi Arabia.

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      A. F. Omar and E. Pérez-López have contributed equally to the study and therefore share first authorship.