Studies on the control of alternate bearing in citrus. VII

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  • カンキツの隔年結果防止に関する研究 (第7報)
  • カンキツの隔年結果防止に関する研究-7-
  • カンキツ ノ カクネン ケッカ ボウシ ニ カンスル ケンキュウ 7
  • Effects of cross-pollination and spraying of chemicals in blooming or young fruit period on fruit set of Washington Navel orange

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Abstract

In growing Washington Navel orange in Japan, poor fruit set has often been a serious problem.<br>In order to investigate the effective means of improving fruit set, solution of urea or several growth regulators were sprayed during the flowering period or about four weeks after petal fall, and at the same time, the effect of cross-pollination with Natsudaidai pollen was examined.<br>1. The fruit set of Washington Navel orange was increased by the application of gibberellin or urea spray in the flowering or young fruit period. Cross-pollination with Natsudaidai pollen also increased the fruit set.<br>2. Combined treatment of cross-pollination and gibberellin or urea spray was more effective than each of single treatment.<br>3. Gibberellin spray seemed to be more effective than cross-pollination with Natsudaidai pollen.<br>4. Gibberellin sprayed in young fruit period was more effective than in flowering period, and there was little difference in its effect between repeated sprays in flowering and young fruit period and a single spray in young fruit period. On the contrary, urea was more effective when sprayed in flowering period than in young fruit period.<br>5. Gibberellin seemed to be more effective at higher concentrations till 500ppm, but the difference between 500ppm and 1000ppm was not remarkable.<br>6. Spraying of some growth regulators-2, 4-D, 2, 4, 5-T, 2, 4, 5-TP and etc.-showed no definite effects in increasing fruit set when they were applied both in flowering and young fruit period.<br>7. On the trees the fruit set of which was very poor because of much more flowers and less leaves, spraying of urea or gibberellin as well as cross-pollination with Natsudaidai showed no effect in increasing fruit set.

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