Frost‐Hardiness in Relation to Leaf Anatomy and Natural Distribution of Several Solanum Species1

Abstract

The objective of this study was to determine anatomical and morphological differences related to the frost‐hardiness of tuber bearing Solanum species. Observations were made on about 2‐month‐old plants of 24 species including seven cultivars of potato (Solarium tuberosum L.). These species vary in frost‐hardiness from −2.5 to −5.5 C.No consistent relationship was found between various gross morphological characteristics of the plants and frosthardiness. However, hardy species (frost killing temperature −4.0 C or colder) usually had short and highly branched stems with smaller and thicker leaves.Among the various anatomical parameters studied, the number and thickness of palisade parenchyma layers and the stomatal index on the upper leaf surface were closely related to frost.hardiness. All hardy species had two palisade layers and all except three non‐hardy accessions (frost killing temperature ‐3.5 C or warmer) had one palisade layer. On the average, hardy species had a three times greater stomatal index (26.7%) than non‐hardy species. (8.8%), on the upper, surface of. the leaf, which. is probably due to two palisade layers m hardy species. The palisade parenchyma occupied a larger portion of the leaf cross section in hardy species (62.8%) compared to non‐hardy species (51.2%). No significant differences in cell size and intercellular space were detected between these two types of species. Ploidy was not related to leaf anatomy or frost‐ hardiness. Among the hybrid plants examined, hardy hybrids had two palisade parenchyma layers.The natural distribution patterns of many wild growing hardy and non‐hardy Solanum species were analyzed. A difference in the geographical distribution of hardy and non‐hardy wild species was found. The hardy species (except S. commersonii Dunal ex Poir.) are found in the high Andes of southern Peru, in central and southern Bolivia, northern Chile, and northwestern Argenina. Non‐hardy wild species are primarily distributed in Mexico, Guatemala, Venezuela, Colombia, Ecuador, and northern and central coastal Peru. A close relationship was found between the altitude of origin of a species or collection and its frost‐hardiness.It appears that anatomical features of hardy species are the results of their adaptation to environmental stress (primarily low temperature and in some cases together with water stress) under natural selection.