THE EFFECT OF TEMPERATURE ON REPRODUCTION IN 5 PRIMULA SPECIES

Primula vulgaris Huds., P, veris L., P. frondosa Janka, and three popu lations of P. farinosa L. were legitimately and illegitimately pollina ted, and the self-fertile P, scotica selfed and cross-pollinated and t hen subjected to uniform temperature conditions of 6, 15 or 26 degrees C for 4 d before gynoecia were examined for pollen germination and po llen tube growth, or plants progressed to seed set at 15 degrees C, af ter which seeds were weighed, germinated, and seedlings grown on. The temperature responses of pollen germination and pollen tube growth wer e not always congruent, and varied between species, populations, and o ften between morphs (pin and thrum) in the distylous species. Neverthe less, optimal temperature responses tended to be lower for vernal spec ies (P. vulgaris and P. veris) and for subarctic P. scotica than for l ater flowering montane species. However, no relationship was found bet ween pollen temperature response, and fertility. The greatest seed set occurred after legitimate pollination at 15 degrees C in most cases; a flowering temperature of 26 degrees C tended to impede seed set, exc ept for P. scotica and the low altitude population of P. farinosa. In P. veris, P. frondosa and the high altitude population of P. farinosa, some illegitimate pollen germination and pollen tube growth occurred at 26 degrees C, but this did not lead to increased within-morph seed set in these self-incompatible species at this relatively high tempera ture. Temperature at flowering frequently affected average seed weight , and in P. veris and two populations of P. farinosa this attribute ma y have been influenced by seed number, the average seed weight of few- seeded capsules tending to be greater than for many-seeded capsules. A high seed weight might mitigate the disadvantageous effects of low fe cundity resulting from interactions with flowering temperature. Howeve r, in P. vulgaris and P. scotica interactions between flowering temper ature and seed weight may have other, undetermined, causes. The seed o f four species germinated least well in standard conditions when set f ollowing a flowering temperature of 6 degrees C, which tends to suppor t the hypothesis that temperature at flowering can affect seed physiol ogy; in contrast the seed of the two upland populations of P. farinosa germinated least well after flowering at 26 degrees C. We conclude th at much more work is needed on interactions between temperature and re productive efficiency, but that preliminary indications suggest that a global increase in temperature at flowering might adversely affect th e quantity and quality of seed set in some species. (C) 1998 Annals of Botany Company.