Mexican papita viroid: putative ancestor of crop viroids.

Abstract

The potato spindle tuber disease was first observed early in the 20th century in the northeastern United States and shown, in 1971, to be incited by a viroid, potato spindle tuber viroid (PSTVd). No wild-plant PSTVd reservoirs have been identified; thus, the initial source of PSTVd infecting potatoes has remained a mystery. Several variants of a novel viroid, designated Mexican papita viroid (MPVd), have now been isolated from Solanum cardiophyllum Lindl. (papita güera, cimantli) plants growing wild in the Mexican state of Aguascalientes. MPVd's nucleotide sequence is most closely related to those of the tomato planta macho viroid (TPMVd) and PSTVd. From TPMVd, MPVd may be distinguished on the basis of biological properties, such as replication and symptom formation in certain differential hosts. Phylogenetic and ecological data indicate that MPVd and certain viroids now affecting crop plants, such as TPMVd, PSTVd, and possibly others, have a common ancestor. We hypothesize that commercial potatoes grown in the United States have become viroid-infected by chance transfer of MPVd or a similar viroid from endemically infected wild solanaceous plants imported from Mexico as germplasm, conceivably from plants known to have been introduced from Mexico to the United States late in the 19th century in efforts to identify genetic resistance to the potato late blight fungus, Phytophthora infestans.

Eggplant Latent Viroid , the Candidate Type Species for a New Genus within the Family Avsunviroidae (Hammerhead Viroids)

“…The sequence identity between some ELVd variants is slightly below 90%, one of the demarcation criteria separating variants of the same viroid from different viroid species (12). A similar situation has been reported for Mexican papita viroid (23), but as in this case, we consider that this sole criterion does not justify creating more than one species for ELVd.…”

Viroids and the nature of viroid diseases*

“…In parallel with the intensive work on the physical/chemical properties of PSTV d, more biologically oriented work resulted in the discovery of many additional members of the viroid family [1,2,22,33,38,46,49,61,67,68].…”

“…Recently, however, a novel viroid, the Mexican papita viroid (MPV d) has been discovered in Mexico, where it harmlessly inhabits a tuber-bearing, wild solanaceous plant, Solanum cardiophyllum [61]. Evolutionarily, MPVd is most closely related to TPMV d and PSTV d. It is known that specimens of S. cardiophyllum have been introduced to the United States in the latter part of the 19th century in efforts to find resistance to the late blight fungus (Phytophthora infestans).…”

Current status of viroid taxonomy

“…Note that two viroid pairs (i.e., MPVd/TPMVd and TCDVd/PSTVd) are much more closely related than any others. In proposing that MPVd and TPMVd be recognized as members of separate species, Martinez-Soriano et al [46] pointed to certain differences in their biological properties, namely, the ability of TPMVd (but not MPVd) to infect Gomphrena globosa and the appearance of flower break in Nicotiana glutinosa inoculated with MPVd or PSTVd (but not with TPMVd). Unfortunately, the lack of experimental details makes it difficult to evaluate the strength of this evidence.…”

“…In addition to tomato, a variety of ornamental species (particularly solanaceous ornamentals) are infected by different pospiviroids [11,64,65]. MPVd was originally isolated from Solanum cardiophyllum growing wild in the Mexican state of Aguascalientes [46], but in 2008, two groups [42,66] detected its presence in samples of cultivated tomato collected elsewhere in that country. To critically compare the biological properties of MPVd and TPMVd, Verhoeven et al [66] carried out two independent series of bioassays involving five different pospiviroids and seven commonly used solanaceous and nonsolanaceous indicator hosts; in addition to TPMVd and MPVd (three isolates), CLVd, TCDVd, and PSTVd (three isolates) were also tested.…”