First report of a Candidatus Phytoplasma asteris infecting tomatillo (Physalis ixocarpa) in Sinaloa, México

M.E. Santos-Cervantes^{1, 2}, J.A. Chávez-Medina¹, J.A. Fierro-Coronado¹, R.D. Ruelas-Ayala¹, M.A. Barreras-Soto^{1, 3}, J. Méndez-Lozano¹ and N.E. Leyva-López^1*

¹ CIIDIR-IPN, Unidad Sinaloa, Juan de Dios Bátiz Paredes 250, Guasave, Sinaloa, México CP 81101
2 Programa Regional de Noroeste para el Doctorado en Biotecnología, FCQB-UAS. Apdo. Postal 1354, Culiacán, Sinaloa, México
3 INIFAP, Campo Experimental Valle del Fuerte, Apdo. Postal 342, Los Mochis, Sinaloa, México

*neleyval@ipn.mx

Accepted for publication 05/10/06

Tomatillo, also called Husk or Green tomato, is an important vegetable in the Mexican diet since it is widely used to prepare many types of salsas and other traditional dishes.  As a result it is produced commercially in 29 of the 32 Mexican states, with a national cultivated area of 53,407 hectares in 2004.  In 2005, a plant disorder was observed in Tomatillo fields from Sinaloa state.  Symptoms were similar to those associated with phytoplasma diseases, such as little leaf, yellowing and leaf deformation (Lee et al., 2000; Fig. 1).

Figure 1: Little leaf, yellowing and leaf deformation symptoms of diseased (left and middle) and asymptomatic (right) tomatillo plants

Leaf samples of 26 plants with symptoms were collected.  Total DNA was extracted (Zhang et al., 1998) and used as template in a nested PCR assay to amplify the phytoplasma 16S rDNA gene using primer pairs R16mF2/R16mR1 and R16F2n/R16R2 (Gundersen & Lee, 1996).  Sixty two percent of the samples produced the expected PCR fragment (1.25 kb) and all samples tested gave the same profile following restriction digestion with AluI, KpnI, MseI, HaeIII and RsaI.  The PCR product was cloned into the pGEM-T easy vector (Promega, Madison, WI) and sequenced.  The amplified 16S rDNA sequence of the phytoplasmas (1246 bp; GenBank accession no. DQ987871) was compared with DNA sequences of other phytoplasmas taken from the GenBank database, using the Clustal V alignment method (MegAlign, DNASTAR software, London).

Figure 2: Phylogenetic distance tree comparing the partial 16S rDNA sequences of the Tomatillo little leaf with those of other phytoplasmas from GenBank. Acholeplasma palmae was used as the outgroup. Bootstrap (confidence) values are shown on the branches. A dotted line on the tree indicates a negative branch length. GenBank accession numbers for sequences are given in parenthesis.

The highest sequence similarity (99%) was obtained with Tomato and Pepper little leaf and Ash witches´-broom phytoplasmas (GenBank accession nos. DQ375238, DQ168882 and AY566302 respectively), which are isolates of Candidatus Phytoplasma asteris (16SrI Aster yellows group) (Fig. 2).  To our knowledge, this is the first report of a phytoplasma associated with a disease of the tomatillo crop in Mexico.

Acknowledgements

This work was supported by Instituto Politécnico Nacional and Fundación Produce Sinaloa.

References

Gundersen DE, Lee IM, 1996. Ultrasensitive detection of phytoplasmas by nested-PCR assays using two universal primer pairs. Phytopathologia Mediterranea 35, 144-151.

Lee IM, Davis RE, Gundersen DE, 2000. Phytoplasma: phytopathogenic mollicutes. Annual Review of Microbiology 54, 221-255.

Zhang YP, Uyemoto JK, Kirkpatrick BC, 1998. A small-scale procedure for extracting nucleic acids from woody plants infected with various phytopathogens for PCR assay. Journal of Virological Methods 71, 45-50.

The British Society for Plant Pathology