Abstract
Twelve genotypes of geranium (Pelargonium × hortorum Bailey) were grown in a greenhouse. Experiments were conducted to identify the response of the geraniums to high-temperature stress in order to develop a method of selection for high-temperature stress tolerance. All of the accessions showed a decrease in chlorophyll content under high-temperature treatments. A significant difference was found in the SPAD ratio I (treatment / no treatment) (SPAD-RI) in twelve accessions. Variation was found in high-temperature stress tolerance among accessions, and one wild species and four hybrid accessions showed a high-temperature stress tolerance. Moreover, a significant correlation was found between leaves and flowers in the value of high-temperature stress tolerance assessment (r = 0.806**), between SPAD-R I and high-temperature stress tolerance assessment value (HTSTAV) of leaves (r = 0.963***), and between SPAD-RI and HTSTAV of flowers (r = 0.747**). Some characters were assessed and rated on a score of one to five. Flower quality was assessed for each accession under high-temperature conditions in August. High-temperature stress tolerance was found in four hybrid accessions. However, there was no significant correlation between the SPAD ratio II (August / no treatment in May)(SPAD-RII) and the value of flower quality assessment. A negative correlation was found between the leaf temperature and SPAD-RII (r = −0.721 **), but it unlike between the leaf temperature and flowering characters. A significant correlation was found between HTSTAV of flowers and the value of flower quality assessment (r = 0.630*). These results suggest that high-temperature stress-tolerant varieties could be selected by high-temperature treatment during the optimum growth period (May in Japan) and then by comparison of certain characters under high-temperature conditions and optimum growth conditions within one year.
