Treating pollen with mutagens prior to controlled pollination may facilitate the production of mutant trees for developmental studies and eventual plantation improvement. To establish a suitable dose of the chemical mutagen ethyl methanesulfonate (EMS) for the testing of this hypothesis, pollen of Eucalyptus globulus ssp. globulus and E. grandis was studied in vitro. Pollen germination, pollen tube elongation and generative cell division were examined after 48 h of culture, following exposure to between 0 and 1,000 ppm EMS. Doses of 600 to 1,000 ppm EMS reduced pollen germination in vitro in both species. Doses of up to 1,000 ppm EMS were not observed to significantly impact on either pollen tube length, or generative cell division in vitro of either species. A dose of 600 ppm EMS in paraffin oil is predicted to induce mutation in Eucalyptus species whilst impacting minimally on seed production based on the effect on pollen germination.
Mutation induction has played an integral role in the improvement of most commercially important crop species but has not been successfully applied to tree species because of their long reproductive cycles which hinder the use of the traditional seed-treatment approaches. Treatment of pollen with a chemical mutagen prior to pollination will, theoretically, allow stable, heterozygous mutant trees to be produced in a relatively short time and might facilitate mutagenesis of tree species. As the first step in testing this hypothesis, a controlled-pollination trial with chemically treated pollen was conducted in Eucalyptus globulus ssp. globulus (Labill.). Assessment of fruit, seed and seedlings from more than 500 pollinations associated mutagenic treatment of pollen with a significant reduction in seed set. Non-significant increases in capsule (fruit) abortion, the inhibition of seed germination and the incidence of aberration in seedlings were also noted. We argue that pollen treatment may be a useful means of producing Eucalyptus mutants with variation in flowering time, salinity and frost tolerance, lignification and other traits of scientific and economic importance.
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