The effect of pollen irradiation on reproductive capacity, seedling growth, and variation of Betula nigra—I. Seed yield, germination, and germinant abnormalities

Abstract

Pollen samples of Betula nigra exposed to 0, 500, 1000, 2000, 4000 and 8000 roentgens (R) of gamma radiation were used in controlled crosses. Pollen irradiation had no effect on the number of female inflorescences developing into mature catkins or on the number of seeds per catkin. Amount of filled seed and germination percentage, however, decreased as the exposure level increased; the 8000 R lots had only 17·8 and 10·9 per cent, respectively, of the controls. Viability of the filled seeds was reduced to 59·7 per cent after exposure to 8000 R compared with 90 per cent or better from all other treatments. Seed from the 8000 R treatment also had a low rate of germination. Germinants having an abnormal number or shape of cotyledons increased in frequency with exposure level up to 13·3 per cent after 8000 R. Non-viable abnormal germinants similarly increased to 12·6 per cent at 8000 R. Pollen irradiation thus has a pronounced detrimental effect on the reproductive capacity of this species. Low levels of radiation appeared to have a stimulating effect on rate and percentage of germination but these differences were not statistically significant. The increase in aberrant seedlings indicates that pollen irradiation may be an effective means of inducing variation in B. nigra.