Phytoplasmas Associated with Elm Yellows: Molecular Variability and Differentiation from Related Organisms

Area of Science:

• Phytopathology
• Molecular Biology
• Plant Bacteriology

Background:

• Elm yellows (EY) is a destructive disease affecting elm trees (Ulmus spp.).
• Phytoplasmas are the causal agents of EY, belonging to group 16SrV.
• Understanding phytoplasma strain diversity is crucial for disease management.

Purpose of the Study:

• To differentiate phytoplasma strains associated with elm yellows using molecular techniques.
• To compare phytoplasma strains from Italy and the United States affecting elms.
• To investigate the genetic diversity of phytoplasmas within group 16SrV.

Main Methods:

• Restriction fragment length polymorphism (RFLP) analysis of polymerase chain reaction (PCR) amplimers.
• Targeting ribosomal DNA and non-ribosomal DNA fragments using specific primer pairs (P1/P7).
• Utilizing restriction enzymes TaqI, BfaI, RsaI, and MseI for DNA digestion and profiling.

Main Results:

• RFLP profiles differentiated elm-associated phytoplasmas from those in other plant species (e.g., Catharanthus roseus, Apocynum cannabinum, Vitis vinifera).
• Specific enzymes (TaqI, BfaI) distinguished elm strains from other 16SrV group members.
• Intra-US elm strains showed variations in ribosomal DNA based on RsaI site presence/absence.
• Italian elm strains were differentiated from American strains using MseI on non-ribosomal DNA.

Conclusions:

• RFLP analysis is effective in differentiating phytoplasma strains associated with elm yellows.
• Distinct molecular profiles exist among elm-associated phytoplasmas from different geographical origins (Italy vs. US).
• Strain HD1 from Apocynum cannabinum associated with EY-diseased elms exhibits unique characteristics.