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Is there a relationship between ethylene evolution, ethylene sensitivity, and needle abscission in root-detached balsam fir?

MacDonald, M.T., Lada, R.R., Martynenko, A.I., Pepin, S., Desjardins, Y., Dorais, M.
Acta horticulturae 2012 no.932 pp. 405-411
Abies balsamea, Christmas trees, abscission, branches, clones, ethylene, ethylene production, genotype, horticultural crops, industry, Canada
Balsam fir is an important horticultural crop of Atlantic Canada, valued at approximately $72 million each year being used as Christmas trees and for greenery products. However, needle abscission adversely affects the industry. A recent study has shown that needle retention duration (NRD) varies widely between individual clones. A separate study confirmed that ethylene reduced NRD in balsam fir. The purpose of this research was to determine if the genotypic variation in NRD of balsam fir might be related to ethylene sensitivity or ethylene production. To test this hypothesis, branches were harvested from two different genotypes (one with low NRD and the other with high NRD) and exposed them to 0, 10, 50, 100, 250, 500, or 1000 ppm ethylene. It was found that daily exposure to concentrations as low as 10 ppm reduced needle retention duration by 20 to 40% in both genotypes, though a concentration of 1000 ppm had the most profound effect. However, ethylene production was significantly higher in the low NRD genotype (19.2 µmol∙g-1∙h-1) than the high NRD genotype (14.1 µmol∙g-1∙h-1). There was also a significant correlation between day of peak ethylene production and NRD (R2=98.7%). It was concluded that there is no significant difference in ethylene sensitivity in the range of 10 to 1000 ppm between the two genotypes, but the genotypes which shed needles earlier had a higher rate of ethylene evolution, suggesting that the rate of ethylene evolution rather than sensitivity to ethylene is linked to needle abscission.