Meiosis in pollen mother cells of Pinus contorta

Abstract

Meiosis in pollen mother cells (PMC) of Pinus contorta Dougl. growing at Röskär (lat. 59°25′ long. 18°11′ altitude 20 m) and Mångbyn (lat. 63°58′ long. 20°24′ altitude 70 m) was investigated. The appearance of the PMC during the different meiotic stages agreed well with most other conifers. The onset of meiosis, estimated as the temperature sum (degree days with +5°C as the critical mean daily temperature) needed to obtain a passing of the pachytene stage by 10 per cent of the PMC, was determined. A direct relationship between the expected temperature conditions at the native habitats and the temperature sum for the onset of meiosis was shown to exist for the trees growing at Röskär. (The origin of the trees growing at Mångbyn was not known with certainty.) The meiosis of the PMC in Pinus contorta appeared simultaneous to or somewhat later than meiosis in the PMC of Pinus silvestris. Owing to the favourable temperature conditions at the time of meiosis the percentage of irregular PMC was low. The distribution of irregularities in different stages agreed fairly well with the situation in other conifers. Based upon the data obtained, it may be concluded that the probability of a proper pollen formation in seed orchards of Pinus contorta in Sweden can be regarded as satisfactory.