Detection and molecular characterization of phytoplasmas associated with vegetable and alfalfa crops in Qassim region

Ayman F Omar

doi:10.1080/17429145.2017.1279357

Abstract

ABSTRACTDuring a survey conducted in Qassim province, Saudi Arabia, in the year in 2015, 120 samples of carrot (Daucus carota subsp. sativus), onion (Allium cepa), faba bean (Vicia faba), green mustard (Brassica juncea) and alfalfa (Medicago sativa) plants displaying symptoms reminiscent of phytoplasma diseases were collected and tested for phytoplasma infection. Phytoplasma-specific PCR products were only amplified from symptomatic plants by nested-PCR. Disease incidence ranged from 3.14% in alfalfa crop fields 1 year after cultivation to 77.48% in 3-year-old fields. In the five carrot fields sampled in this study, the incidence changed from 3.2% to 100% after 7 months of cultivation. Phylogenetic analysis revealed that all Qassim phytoplasma isolates belong to the 16SrII group. Most of them shared 100% identity with papaya yellow crinkle (16SrII-D Y10097). The results from phylogenetic and virtual restriction fragment length polymorphism analyses of the 16S rRNA gene sequence confirmed that the phytoplasma of Qassim isolates under study is a member of 16SrII-D subgroup. To the best of my knowledge, the onion and green mustard are considered new hosts for the 16SrII group; therefore, this is the first report on the association of phytoplasma with diseases of faba bean, onion, carrot, mustard and alfalfa in Qassim province, Saudi Arabia.

Highlights

Plant-pathogenic phytoplasmas are unique prokaryotic microbes that lack cell walls
Phytoplasma diseases were observed in many vegetables and alfalfa crops in
The experimental plant areas of onion, faba bean and green mustard are very close to each other, the incidence of disease varied according to the crop, which was for onion, faba bean and green mustard 1.3%, 47.5% and 4.5%, respectively (Table 2)

Summary

Introduction

Plant-pathogenic phytoplasmas, first described as mycoplasma-like organisms, were discovered by a group of Japanese scientists in 1967 (Doi et al 1967). They belong to the class Mollicutes, and have been recently classified within the provisional genus “Candidatus phytoplasma” based on 16S rDNA sequence analysis (IRPCM Phytoplasma/Spiroplasma Working Team–Phytoplasma Taxonomy Group 2004). They severely affect more than 700 economically important plant species including vegetables, cereals, fruits and ornamentals, as well as forage and forest plants that are found worldwide. In Al-Qassim region, alfalfa, carrots and onion are very important crops where the cultivated area is 20,069, 3828 and 300 ha with an average annual production of 435,103, 88,023 and 6759 metric tons, respectively (Agricultural Statistical Year Book 2012)

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Results