Temperature-dependent enhancement of pollen tube growth observed in interspecific crosses between wild Cucumis spp. and melon (C. melo L.)

Abstract

Wild Cucumis spp., which have resistance to various diseases, have the potential to be used for melon (C. melo L.) breeding. Nevertheless, few interspecific hybrids between melon and wild Cucumis spp. have been obtained because of strong reproductive barriers such as pollen–pistil incongruity and hybrid seed abortion. For this study, we examined the temperature conditions enhancing pollen tube growth and fruit set in interspecific crosses between melon and wild Cucumis spp. Before temperature-conditioned pollination, four wild Cucumis spp. were pollinated with the melon line ‘MR-1’ and two lines of C. anguria, PI 147065 and PI 320052, and a line of C. metuliferus, PI 526242, were selected for later experiments. These three lines were crossed reciprocally with ‘MR-1’ under controlled temperatures of 24–34°C at 2°C intervals. When ‘MR-1’ pistils were pollinated with three lines of wild Cucumis spp., pollen tube growth was arrested after germination at all temperatures. However, in the pistil of wild Cucumis spp., pollen tube growth of ‘MR-1’ was significantly greater at 32°C and at 34°C than that under 30°C. Furthermore, pollen tube length in pistils of PI 320052 and PI 526242 at 32°C was comparable to that of ‘MR-1’ self-pollination at 28°C. Fruit set frequency was also improved at 32°C. These results demonstrated that the pollen tube inhibition of Cucumis spp. interspecific crosses might be partially or fully recoverable in higher-temperature conditions. Moreover, 32°C is apparently the threshold temperature for promoting pollen tube growth in these cross combinations.