‘Washington’ navel orange [Citrus sinensis (L.) Osb.] orchards in Israel suffer from creasing – a physiological disorder of the fruit, leaving the fruit unsuitable for the fresh fruit market. Many ‘Washington’ navel orchards tend to bear small size fruit with low market value. This paper presents two experiments, in which the effects of naphthaleneacetic acid (NAA, 300 mg·L-1) on yield, fruit size, fruit quality and the incidence of creasing of ‘Washington’ navel orange were examined. The NAA effects were compared to those of gibberellic acid (GA3, 20 mg·L-1) – the common treatment for creasing reduction. In the first experiment, 36% of the fruit of the control trees suffered from severe creasing. The NAA sprays in May (at 18-mm fruitlet diameter) and in June (at 30-mm fruitlet diameter) reduced the incidence of creasing to 9 and 6% respectively, while the GA3 spray at August reduced the incidence of creasing to 17% of the fruit.
Two sequential sprays – the first with NAA in May and the second with GA3 in August reduced the incidence of creasing to only 3% of the fruit. The early NAA spray (May) thinned 14% of the fruitlets and increased the size of the remaining fruit. The other treatments didn’t thin fruit and had no effect on the fruit size. The treatments had no effect on the total yield. In the second experiment, 54% of the fruit of the controls suffered from severe creasing. NAA sprays in June and July reduced the incidence of creasing to 16 and 14% of the fruit, respectively. The GA3 spray in July reduced the incidence of creasing to 25% of the fruit. Two sequential sprays: NAA in June and GA3 in July reduced the incidence of creasing to only 6% of the fruit. The different treatments had no effect on fruit size nor on the internal quality of the fruit. These data suggest that NAA sprays on large fruitlets, at a timing that doesn’t affect fruit size or thin fruitlets, is effective for creasing reduction. When fruit thinning and enlarging fruit size is also desired, the NAA spray should be applied on fruitlets when they are smaller in size. When a major effect on creasing reduction is desired, two sequential sprays – the first with NAA and the second with GA3 are recommended.
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Source
J. Greenberg, S. Holtzman, M. Fainzack, Y. Egozi and B. Giladi
Ministry of Agriculture, Isreal