HortScience 36(2): 341-343. (2001)
Temperature Effects on Interspecific Hybridization between Gladiolus x grandiflora and G. tristis
Yasumasa Takatsu, Masakazu Kasumi, Toru Manabe, and Mikio Hayashi
Plant Biotechnology Institute, Ibaraki Agricultural Center lwama, Nishi-ibaraki, Ibaraki 319-0292, Japan
Eiichi Inoue, Wataru Marubashi, and Masaru Niwa
School of Agriculture, Ibaraki University, Ami, Inashiki, Ibaraki, 300-0393, Japan

Effect of air temperature on success of interspecific crosses. Air temperature had a marked effect on fertility in controlled crosses (Fig. 2). At 20°C, the pollen tube elongated very rapidly, fertilization was accomplished 12 h postpollination, and the fertility increased to 89.9% 5 d postpollination. At 15 and 25°C, pollen tube elongation slowed, fertilization was first observed 3 and 1 d postpollination, and the final fertility increased to only 76.4% and 73.2%, respectively. At 30°C, pollen tube elongation was inhibited more and the final fertility was very low (1.4%). The final rate of fruit set decreased from 73.1% to 0.0% as the temperature increased, but pollen tube growth and fruit set were found even at 30°C following self-pollination of 'Traveller' (Fig. 3). Crossing barriers frequently occur in interspecific crosses, but sexual barriers preventing crossing have been separated into pre- and postfertilization barriers (Van Tuyl, 1997). In this study, the results of self-pollination of 'Traveller' indicated that female fertility is good at 30°C. Although fertilization was observed in interspecific crossing at 30°C, no fruit set was obtained. The best temperature for fertilization was 20°C (Fig. 2), but that for fruit set was 15 °C (Fig. 3). These results show that postfertilization barriers inhibit interspecific hybridization between 'Traveller' and G. tristis, and may explain the failure to obtain hybrids without embryo rescue (Takatsu et al., 1996). Our results suggest that lower air temperatures (15 to 20°C) increase fertility and may be appropriate to help overcome postfertilization barriers when hybridizing G. x grandiflora and G. tristis. Humidity and air temperature is very high (over 30°C) in summer in Japan; thus, crossing in autumn is preferred if the flowering time can be controlled.

Fig. 3. Final rate of fruit set [(number of enlarged pod with matured seeds/total number of pod) x 100] at 15, 20, 25, and 30°C, in interspecific hybridization between G. x grandiflora 'Traveller' and G. tristis (Interspecific), and in self-pollination of 'Traveller' (Self). Fruit set was confirmed at 30 d after pollination.

Production of interspecific hybrids. Since the first report by Heller (1973), flow cytometry has been used in plant science (Bergounioux et al., 1992; Galbraith, 1989). It is especially useful for easy, rapid, and accurate determination of ploidy level. Table 1 summarizes the results of chromosome counting and flow cytometric analysis. The chromosome number correlated with fluorescence intensity (r = 0.98**) in G. x grandifiora and G. tristis, and the diploid species G. tristis showed one-half the fluorescence intensity of the tetraploid species G. x grandiflora. This suggests that estimating the ploidy levels of hybrids between these two species by flow cytometry is possible.

Eighty-four seeds matured completely, and 28 seedlings (33.3%) grew after sowing, but only 18 plants (21.4%) flowered normally. F1 seedlings obtained by interspecific hybridization showed intermediate value of fluorescence intensity between G. x grandiflora and G. tristis by flow cytometric analysis (Table 1). Table 2 lists descriptive data for the F1 plants, whose chromosome number was 45. Most F1 plants exhibited some degree of male sterility. F1 plants had intermediate floret numbers, floret width, leaf number, and leaf width. The total height was measured as the spike length in G. x grandiflora and hybrids, but G. tristis has a long flowering stem instead of a spike, indicating that the F1 plants were hybrids of these parents. These plants showed a variety of flower colors [vivid pink, light pink, and light pink (with or without) a white stripe], but they lacked fragrance.

CybeRose note: It is apparent from the chart that a mixture of pollen from 'Traveller' and Tristis should yield more Self offspring at 25°C, and more Interspecific at 15°C.

Ebey (1932) reported that William Henderson overcame the difficulty of breeding with G. tristis by planting the plants next to other glads, and letting the night-flying Egyptian moths do the pollination.

Cape Bulbs (1994)
Richard L. Doutt

Gladiolus tristis was named by Linnaeus in 1762. The word tristis means "dull colored" or "sad," though why Linnaeus should describe the flowers in this way is puzzling. Gardeners who grow G. tristis are certainly not likely to call this elegant species the "sad glad." It is sometimes termed the marsh Afrikaner because it is common in seasonally marshy areas, called vleis in Afrikaans. South Africans also call these flowers white, evening-scented aandbloome, meaning "evening flowers" in Afrikaans. Cut flowers give off a delicious perfume, which has been variously described as strong carnation, clove pink, almond, violet, night-scented stock, honeysuckle, magnolia, and sweet rocket. While the flowers in nature are fragrant only at night, they will also become fragrant in midday if placed in a dark closet (Poindexter, 1931). The scent of G. tristis attracts moths for pollination.

Also see: Delp: Heat in Hybridizing Rhododendrons (1980)