Effect of potato spindle tuber viroid variants and infection stage on seed transmission through pollen.

Viroids are small, proteinless single-stranded circular RNAs. In plants, they can be transmitted via infected pollen and seeds. The effectiveness of viroid transmission through pollen depends on both the viroid and host species. It is, however, unclear whether viroid variant type or infection stage influences seed transmission through pollen. In the present study, we collected pollen from petunia infected with nine different variants of the potato spindle tuber viroid (PSTVd) at various stages after inoculation and used the material to pollinate healthy plants. Five and eight PSTVd variants were transmitted by pollen at 3 and 6 mpi respectively. All variants were pollen-transmissible at 9 mpi. The foregoing results indicated that seed transmission of PSTVd through pollen collected from infected donor plants may depend on the time elapsed since inoculation. For variant no. EU862231, however, the rate of seed transmission via pollen may depend on the pollen viroid titre. Nevertheless, there was no apparent correlation between the transmission rate and the pollen viroid titre in the U23058 or V01465 variant. Hence, the relationship between the viroid transmission rate and the pollen viroid titre may depend on the viroid variant type.

Surveys in the Chrysanthemum Production Areas of Brazil and Colombia Reveal That Weeds Are Potential Reservoirs of Chrysanthemum Stunt Viroid.

The stunting disease, incited by chrysanthemum stunt viroid (CSVd), has become a serious problem in chrysanthemum production areas worldwide. Here we identified 46 weed species from chrysanthemum fields in two producing regions of the State of São Paulo, Brazil. The mechanical inoculation of these weeds with a Brazilian CSVd isolate revealed that this viroid was able to infect 17 of these species, in addition to chrysanthemum, tomato and potato. Plants of Oxalis latifolia and chrysanthemum naturally infected with CSVd were found in chrysanthemum fields in Colombia, which is the first CSVd report in that country. Therefore, weeds have the potential to act as reservoirs of CSVd in the field. These results are the first reports of experimental CSVd infection in the following species: Amaranthus viridis, Cardamine bonariensis, Chamaesyce hirta, Conyza bonariensis, Digitaria sanguinalis, Gomphrena globosa, Helianthus annuus, Lupinus polyphyllus, Mirabilis jalapa, Oxalis latifolia, Portulaca oleracea and Catharanthus roseus. The phylogenetic analyses of the CSVd variants identified herein showed three groups with Brazilian CSVd variants distributed in them all, which suggests that Brazilian CSVd isolates may have different origins through successive introductions of infected germplasm of chrysanthemum in Brazil.