| Popis: |
Four days of 90% shading at the time of fruit setting (1–5 days after petal fall, DAPF) of mature ‘Jonagold’/M.9 apple trees was combined with the application of thinning agents to establish the possible interaction of both main treatments on fruit retention, and the effects of the main treatments on fruitlets CO2 exchange and their carbohydrate concentration. Shading alone reduced yield by up to 35%. When shading was followed by the application of 15 ppm 1-naphthaleneacetic acid (NAA) or 50 ppm 6-benzyladenine (BA), the interaction between shading and chemical thinners was on the border of significance. Following the assumption that abscission was induced by shading before the application of chemical thinning agents, the same process of diminished dark respiration rate (Rd) was found on fruitlets sampled 3 days after the end of shading and 7 days after NAA and BA spraying, i.e. in the fruitlets that were considered prone to drop. A week after the end of shading the abscission of fruitlets due to shading was completed and on the remaining fruitlets that were not prone to abscission any more, larger negative net CO2 assimilation rates (A) and enhanced Rd were recorded. Fruitlets prone to abscission sampled 2 days after the end of shading showed a lower concentration of glucose and ascorbic acid and a higher concentration of starch. Eight days after the end of shading, the fruitlets from shaded trees that were not prone to abscission any more contained less fructose while the fruitlets from NAA and BA sprayed trees had a higher concentration of fructose a week after application. The results do not support the hypothesis that a good assimilate supply is needed for the retention of apple fruitlets, because the fruitlets retained on trees expressed even stronger CO2 loss and because the concentration of non-structural carbohydrates did not decrease in fruitlets prone to drop with the exception of glucose. |
Full Text from ScienceDirect