Research Institute of Pomology and Floriculture, 96100 Skierniewice, Poland
Agriculture University, Department of Ornamental Plants, 71424 Szczecin, Poland
Disease symptoms including leaf chlorotic and necrotic spots and stripes resembling freesia leaf necrosis (disease of unknown etiology ) were observed in freesia (Freesia × hybrida Klatt.) plants (cvs. Aladyn, Blue Lady, Cortine, Gompy, and White Rapid) naturally infected with Freesia mosaic virus (FMV) and grown in the greenhouse in Poland. The aim of this work was to study the association of the leaf symptoms occurring in freesia cultivars with phytoplasma infection and to identify it. To detect the possible presence of phytoplasmas in freesias, plants showing leaf symptoms (five cultivars) and symptomless plants (‘Blue Lady’, ‘Cortine’, and ‘Gompy’) were assayed for the presence of phytoplasma 16S rDNA fragment by polymerase chain reaction (PCR). For phytoplasma detection samples of young leaves and corms of 15 symptomatic and five symptomless freesias were taken. The samples were collected from the selected plants infected with FMV. In addition, leaf samples from healthy Catharanthus roseus plants and those infected with AKV reference strain of aster yellows (AY) phytoplasma group, subgroup I-B (supplied by W. Jarausch, INRA Bordeaux, France), were included for comparison. The amplification was performed using the universal—rA/fA or R16F1/R0 and group specific—R16(I)F1/R1 phytoplasma primer pairs (1). Phytoplasma identification was accompanied by digestion with AluI and MseI restriction endonucleases and restriction length polymorphism (RFLP) analysis of the R(I)F1/R1 or rA/fA products. DNA amplification product was observed in all nested PCRs containing template DNA derived from the leaves and corms of all symptomatic as well as symptomless and FMV-affected freesias except symptomless freesia ‘Cortine’. Based on RFLP analysis of PCR products and the comparison of the RFLP patterns with those of the strain AKV of aster yellows phytoplasma group (AY I-B), the associated phytoplasmas were identified as phytoplasma 16S rRNA group I, subgroup B. This work provides the first evidence that freesias examined were naturally infected with aster yellows phytoplasma. Detection of phytoplasma in diseased and symptomless but FMV-affected freesias underlines the need to know the role of this pathogen in the etiology of freesia diseases.
References: (1) I.-M. Lee et al. Phytopathology 84:559, 1994. (2) H. J. M van Dorst. Neth. J. Plant Pathol. 79:130, 1973.