Identification of aster yellows phytoplasma in garlic and green onion by PCR-based methods.

In the summer of 1999, typical yellows-type symptoms were observed on garlic and green onion plants in a number of gardens and plots around Edmonton, Alberta, Canada. DNA was extracted from leaf tissues of evidently healthy and infected plants. DNA amplifications were conducted on these samples, using two primer pairs, R16F2n/R2 and R16(1)F1/R1, derived from phytoplasma rDNA sequences. DNA samples of aster yellows (AY), lime witches'-broom (LWB) and potato witches'-broom (PWB) phytoplasmas served as controls and were used to determine group relatedness. In a direct polymerase chain reaction (PCR) assay, DNA amplification with universal primer pair R16F2n/R2 gave the expected amplified products of 1.2 kb. Dilution (1/40) of each of the latter products were used as template and nested with specific primer pair R16(1)F1/R1. An expected PCR product of 1.1 kb was obtained from each phytoplasma-infected garlic and green onion samples, LWB and AY phytoplasmas but not from PWB phytoplasma. An aliquot from each amplification product (1.2 kb) with universal primers was subjected to PCR-based restriction fragment length polymorphism (RFLP) to identify phytoplasma isolates, using four restriction endonucleases (AluI, KpnI, MseI and RsaI). DNA amplification with specific primer pair R16(1)F1/R1 and RFLP analysis indicated the presence of AY phytoplasma in the infected garlic and green onion samples. These results suggest that AY phytoplasma in garlic and green onion samples belong to the subgroup 16Sr1-A.

A test for measuring growth responses of mollicutes to serum and polyoxyethylene sorbitan.

A test is described that is useful for characterizing mollicutes in terms of the ability to maintain growth in medium containing 15 to 20% fetal bovine serum or in serum-free media with or without 0.04% Tween 80 (polyoxyethylene sorbitan). Representative Acholeplasma species maintained growth in serum-free medium, and about half of the strains tested grew well in Tween 80-supplemented medium. Representative Mycoplasma and Entomoplasma species did not maintain growth in either serum-free medium alone or when Tween 80 was added. Spiroplasma species and group representatives generally failed to sustain growth in serum-free medium with or without Tween 80, but at least four of the spiroplasmas tested maintained growth in serum-free medium. The representative Mesoplasma species grew in serum-free media only when Tween 80 was added, as did Mycoplasma lactucae. Although the test has obvious determinative uses for members of the class Mollicutes, it does not supplant the conventional methodology for assaying the cholesterol requirements of these organisms.