Effect of season, plant age and temperature during plant growth on compatible and incompatible pollen tube growth in Petunia hybrida

In Petunia hybrida the length of pollen tubes was measured after growth in the style for 24 h. The length attained depends upon the temperature regime under which the pollen as well as the styles developed prior to pollination. The temperature regimes used were 25.5/18°C and 19.5/18°c respectively, both in a 16/8 h day/night regime. A high temperature regime during the progamic phase causes a greater length of the tubes than the low temperature regime; this difference is larger after cross- than after self-pollination. The length after 24 hours’ growth of incompatible pollen tubes is larger when the pollen developed, prior to pollination, under the high temperature regime than under the low one, but their length is not affected by the temperature at which the styles developed. With compatible pollen tubes, on the other hand, that length is larger when the styles developed under the high temperature regime than under the low one and it is also enhanced by a pretreatment of styles, developed under a low temperatue regime, with the higher temperature for 24 h. The enhancement is largest when the treatment precedes pollination at the low temperature regime immediately and is absent when the time between treatment and pollination exceeds four weeks. The length of incompatible pollen tubes after 24 h is in general lower in plants cultivated from summer- than from winter-cuttings; the length of compatible pollen tubes in plants cultivated from winter-cuttings decreases with the age of the plant, if style development and tube growth take place under the low temperature regime. Compatible pollen germination is affected by a low temperature regime during style development and progamic phase. The incompatible pollen germination rate is lower in pollen from summer- than from wintercuttings, when pollen development and pollination occur at the low temperature regime.