Artificial shading reduces the occurrence of double pistils in 'Satohnishiki' sweet cherry

The effect of artificial shading in summer and early autumn on the occurren ce of double pistils in 'Satohnishiki' sweet cherry was studied. Potted tre es were grown in steel frame structures covered with woven shade cloth made of silvered polyethylene and providing 53% and 78% light reduction, from 2 3rd July to 4th October in 1995 and from 16th July to 16th September in 199 7. In 1995, shading levels of 53% and 78% reduced the daily maximum air tem perature by 1.8 degrees C and 3.2 degrees C, respectively, compared to the unshaded control. Forty-seven percent of the buds on nonshaded trees formed double pistil primordia, and 51% of them developed into flowers with doubl e pistils the following spring. Reducing light 78% reduced the frequency of double pistils to 24% in buds and 1.5% at anthesis. whereas 53% shade redu ced the frequency of double pistils only slightly. Doubling was classified into three groups based upon relative length of the two pistils: (1) one pi stil much shorter than the other (S), (2) one pistil about half the length of the other (M), and (3) pistils of approximately equal length (L). The fr equency of flower primordia with equally developed pistils in autumn buds c orresponded to that of flowers with double pistils at anthesis. A 78% level of shading markedly reduced the rate of flower primordia with two equally developed pistils. Because of the relatively cool summer in 1997, the frequ ency of double pistils in autumn buds, even under unshaded conditions, was about half of that in 1995, but shadings still reduced the frequency of dou ble pistils to less than 3%. These results suggest the possibility of apply ing artificial shading to reduce the occurrence of double pistils in 'Satoh nishiki' sweet cherry grown in regions with hot summers. (C) 2000 Elsevier Science B.V. All rights reserved.