Subgenus Leptostemonum Research Articles

A New Species of Solanum Subgenus Leptostemonum (Solanaceae) from Northeastern Mexico

A New Species of Solanum Subgenus Leptostemonum (Solanaceae) from Northeastern Mexico

Host Ranges of Globodera Species Within Solanum Subgenus Leptostemonum

Host ranges of 35 populations of Globodera spp. from the Americas and pathotypes from Europe were tested on 19 Solanum subgenus Leptostemonum spp. representing different taxonomic sub-groupings and geographical distributions. Cluster and principal co-ordinate analyses showed intraspecific variation in all Globodera spp. except G. tabacum. European populations of pathotypes Ro1 to Ro5 and Pa2 had smaller host ranges than populations of Globodera from the Americas and hypotheses are advanced to explain the phenomenon. North and Central American Globodera spp. could not be differentiated; similarities between populations of different species were often equal to or greater than those within the same species. G. airginiae and the Mexican cyst-nematode were most similar followed by G. solanacearum and G. tabacum. G. pallida and G. rostochiensis were more distinct. The pattern of resistance did not correspond directly to taxonomic sub-groupings of Leptostemonum as sections, e. g. Acanthophora and Lasiocarpa, contained resistant and susceptible species. A closer correspondence was found with geographical distribution of solanums; indigenous Old World species with little or no exposure to Globodera were uniformly susceptible, whereas resistance was found in indigenous American solanums likely to have been in contact with Globodera. The hypothesis is advanced that susceptibility is the basic condition in Solanum and that resistance has been selected in response to nematode attack, circumvention of resistance subsequently arising in some Globodera populations.

Allozyme Variation and Evolution in Solanum Section Androceras

Four populations of two climax perennial species and 19 populations of eight colonizing annual species of section Androceras were surveyed for allozyme variation controlled by seven genes. Most populations of the annuals were mono- morphic at all seven loci. Populations of perennials were substantially more variable. It is postulated that genetic bottlenecks associated with colonization may explain the low levels of variability encountered in annual populations. Speciation in section Androceras seems to be universally accompanied by evolution of internal barriers to hybridization that cause hybrid seeds to abort. The strength of these barriers is correlated with interpopulation genetic distance, suggesting that they arise as inci- dental by-products of divergent evolution. Interspecific genetic distances in section Androceras do not indicate an unusually rapid rate of speciation, and taxonomic species diversity in Solanum may instead reflect great age of the genus. A biochemical similarity dendrogram based on genetic distance is in overall agreement with esti- mates of phylogeny in section Androceras based on other criteria, but several taxa seem to be misplaced. Effects on genetic distance of natural hybridization and vari- ance associated with the small sample of genes may be responsible for errors in phylogenetic interpretation. Section Androceras (Nutt.) Bitt. ex Marzell includes 12 of the ca. 2000 species in Solanum. The section has recently been a subject of intensive systematic investigation, leading off a projected series of studies on tax- onomy and evolution in sections of the prickly subgenus Leptostemonum

SOLANUM VERBASCIFOLIUM L., MISIDENTIFICATION AND MISAPPLICATION

SummaryThe common unarmed pantropical species of Solanum traditionally known as S. verbascifolium L. must be called S. erianthum D. Don. The Linnaean type specimen of S. verbascifolium is no 248.1 of the Linnaean herbarium (LINN) and belongs to the prickly subgenus Leptostemonum.