Relation of in vivo morphology to isolation of plant spiroplasmas

Abstract

Two procedures were developed to isolate plant spiroplasmas directly onto DG-2 agar plates or in DG-2 broth without subcultures or dilutions. The frequency of successful spiroplasma isolations was increased by centrifuging samples, after passing through a 0.45-μm filter, at 25,000 × g for 1 h. Spiroplasmas were obtained from peach, cherry, Madagascar periwinkle, and celery with typical symptoms of the Green Valley strain of X disease (GVX), from peach with typical symptoms of the peach yellow leaf roll strain of X disease (PYLR), from Madagascar periwinkle with typical symptoms of aster yellows (AY), from celery with atypical symptoms of GVX (mild GVX), from plantago with atypical symptoms of aster yellows (mild AY), and from stubborn-diseased citrus. Isolations were consistent (>90%) from plants with mild GVX, mild AY, and citrus stubborn, while isolations were inconsistent (0–9%) from plants with typical symptoms of GVX, PYLR, and AY. The role of the isolated spiroplasmas in plant disease was not determined in this study. All spiroplasma isolates were serologically indistinguishable fromSpiroplasma citri. Spiroplasmas were seen in electron micrographs of 8 out of 9 examined plants from which spiroplasmas were isolated. However, electron micrographs of all 13 examined plants from which no spiroplasmas were isolated contained mycoplasma-like organisms (MLOs) but no, spiroplasmas. These results indicate that there is a correlation between helical MLOs in vivo and successful isolation of spiroplasmas, and that plants may be infected with bothS. citri and nonhelical mycoplasmas.