Assessment of Potential Organic Pollenicides as Apple Blossom Thinners

Abstract

The potential of six products to act as pollenicides on apple pollen both in vivo and in vitro was evaluated. The six candidate pollenicides used were lime sulphur (LS) (1.15% solution), ammonium thiosulphate (ATS) (0.75% solution), Surround™ WP (S) (59.2 g/L), biodiesel (BD) (5% emulsion), sodium chloride (NaCl) (8 g/L) and Horticultural-Vinegar (HV) (2% solution). It was found that ‘Golden Delicious’ blossoms that were treated with ATS, LS, S or NaCl had significantly fewer pollen grains that germinated in vivo than the treatment receiving no spray. The effect of the six candidate pollenicides was also investigated in vitro by spraying ‘McIntosh’ pollen with the candidate pollenicides and examining pollen germination, pollen tube growth length and the proportion of unviable pollen grains. All of the treatment sprays significantly reduced pollen germination compared with the control, with ATS and LS resulting in considerable reduction in pollen tube germination and HV completely hindering germination. Among those treatments that allowed some germination, only LS, ATS and BD effectively reduced the mean length that the pollen tubes grew in vitro. These laboratory results are compared with those generated in a parallel field trial to assess what stage of pollination the candidate pollenicides are targeting. Taken together these results indicate that ATS reduces pollen viability and germination on pollinated stigmas and on germination medium and is an effective blossom thinner in the field. Lime sulphur has a greater effect on pollen tube germination and growth on germination medium and is a good thinner in the field and that NaCl reduces pollen germination on pollinated stigmas and is an effective mild thinner in the field. Finally, this research suggests that while BD was an effective thinner in the field, it has less pollenicidal and greater phytotoxic effects than the Other products tested.