M. 1982. The inhibitory effect of gibberellic acid on flowering in Citrus. Plant,.The application of gibbereilic acid (GA3) at any time from early November until bud sprouting, resulted in a significant inhibition of flowering in the sweet orange [C. sinensis (L.) Osbeck] and the Satsuma (C. unshiu Marc.) and Clementine (C reticulata Blanco) mandarins. Two response peaks were evident: the first occurred when the application was timed to the translocation of an unknown flowering signal from the leaves to the buds. The second occurred during bud sprouting, at the time the flower primordia were differentiating. From the pattern of flowering, it appears that the mechanism of inhibition was similar irrespective of the timing of GA3 application. There was an initial reduction in bud sprouting affecting selectively those buds originating leafless inflorescences. An additional inhibition resulted in a reduction in the number of leafy inflorescences with an increase in the number of vegetative shoots, suggesting the reversion of a floral to a vegetative apex. The inhibited buds sprouted readily in vitro but invariably vegetative shoots were formed, A continuous influence of the sustaining branch is necessary to keep the flowering commitment of the buds; irreversible commitment occurs when the petal primordia are well differentiated.Additional key words -Bud dornnancy, bud sprouting. Citrus reticulata, Citrus sinensis. Citrus unshiu. J. L. Guardiola et ai.,
accumulation in the leaves started by early December, and the levels in the leaves were, 34 until bud sprouting, the same in on and off trees. The heavy flower formation which 35 followed an off year caused the rapid mobilization of the stored reserves, which were 36 exhausted at full bloom. We could not find evidence for carbon fixation regulation by 37 fruit demand or by the carbohydrate levels in the leaves. The carbohydrate reserves 38 played no role in fruit set, which relied on current photosynthesis. Koch, 1996). This behaviour is similar to that described in deciduous fruit trees, which 52 accumulate carbohydrate reserves before leaf fall and utilise them during the dormant 53 season and the spring growth (Schaffer et al., 1999), except for some differences in the 54 partitioning of the reserves, and their importance in plant growth regulation and 55 survival. In deciduous trees, the root system is the major storage organ for 56 carbohydrates (Loescher et al., 1990). In Citrus, the root system may still be the major 57 storage organ for carbohydrates, but carbohydrates also accumulate in the leaves at a 58 high concentration (Goldschmidt and Golomb, 1982). The importance of reserve 59 carbohydrates in deciduous trees seems evident. Winter respiration and the beginning of 60 both vegetative and, in some species, reproductive growth, occur in the absence of 61 photosynthesing leaves, and must be totally dependent on reserves (Loescher et al., 62 1990). On the contrary, photosynthesis proceeds in Citrus during winter at a rate high 63 enough to affect growth significantly (Syvertsen et al., 1997; Goldschmidt ,1999). 64Therefore, the reserves should not be as critical for winter and spring growth as in 65 deciduous trees, yet a role for carbohydrate reserves in some aspects of development has 66 been postulated. 67The accumulation of reserves is inversely related to crop load (Goldschmidt and 68 Golomb, 1982), and a depletion of them under heavy crop load has been related to tree 69 collapse (Smith, 1976) and the triggering of an alternate bearing habit (Monselise and 70 Goldschmidt, 1982; Guardiola ,1992; Syvertsen and Lloyd, 1994 carbohydrates (Smith, 1976; Goldschmidt and Golomb, 1982), carbohydrate levels are 73 not the sole factor regulating flower formation (Goldschmidt, 1999; García-Luis and 74 Guardiola, 2000). During flower formation and fruit set, part of the reserves are 75 translocated to the reproductive organs (Akao et al., 1981), but the contribution of the 76 reserves to these processes must vary widely as indicated by the rate of their depletion. 77This rate of depletion may vary among cultivars (Borrás et al., 1984; González-Ferrer et 78 al., 1984), but differences in the rate of depletion within a cultivar have also been 79 reported (García-Luis et al., 1988; Ruiz and Guardiola, 1994; Ruiz et al., 2001). The 80 rate of depletion has been related to flower number (García-Luis et al., 1988). 81There are some studies about the significance of reserves in alternate bearing...
In the Satsuma mandarin (Citrus unshiu Marc.) the presence of the fruit results in a gradual inhibition of flowering and of bud sprouting. This inhibitory effect starts several months before the onset of the winter rest period and lasts until the end of the accumulation of carotenoids in the fruit peel, more than one month after the completion of fruit growth. During all this time and until natural bud sprouting, flowering and bud sprouting are inhibited by exogenous gibberellic acid. Peak responses to this growth regulator coincide with periods of maximal rates of flowering inhibition by the fruit. Kinetin and abscisic acid, applied at the time of peak response to gibberellic acid, inhibited flowering and reduced the number of shoots developed through the reduction of the number of shoots formed per sprouted node, but failed to reduce the number of nodes which sprouted. The same pattern of sprouting was obtained in trees treated with gibberellic acid during the winter rest period or several months earlier. It is concluded that some step leading to flowering and which determines the differences in sensitivity of the buds to this growth regulator has taken place already at this early date.
ElsevierGonzález Nebauer, S.; Arenas, C.; Rodríguez Gamir, J.; Bordon, Y.; Fortunato Almeida, A.; Monerri Huguet, MC.; Guardiola Barcena, JL.... (2013). Crop load does not increase the photosynthetic rate in Citrus leaves under regular cropping conditions. A study throughout the year. Scientia Horticulturae. 160:358-365. doi:10.1016Horticulturae. 160:358-365. doi:10. /j.scienta.2013 Abstract: The objective of this work was to study the influence of fruit load on CO2 assimilation in the leaves of citrus trees presenting alternate bearing habits, and the importance of this factor on photosynthetic rate variability throughout the year and under regular cropping conditions. The photosynthetic rate was measured on 60 days throughout the year on field-grown sweet orange plants under natural conditions in the Valencian Community, the most important citrus-producing area of Spain. The experiments were performed on the 'on' (high crop) and 'off' (low crop) bearing 40-yearold Salustiana sweet orange trees growing in the same orchard. Gas exchange and fluorescence parameters were measured during the year in young and old leaves on sun-exposed branches with and without fruit in the 'on' trees, and in fruitless branches of the 'off' trees. In non-manipulated Citrus trees, fruit load has no significant effect in any season on the photosynthetic rate in the leaves from branches without fruit. However, in high crop trees, the leaves of branches bearing fruit present a slightly lower photosynthetic rates (approx. 10%) than those of fruitless branches. Variations in mineral content (N, K and P) might explain not only these differences, but also the lower photosynthesis rate observed in old leaves (13 to 24 month-old leaves). Environmental conditions were the main factor for the variation of the photosynthetic rate, with variability of the monthly mean photosynthetic rate being much lower than that between days in the same month.1 The objective of this work was to study the influence of fruit load on CO 2 assimilation 12 in the leaves of citrus trees presenting alternate bearing habits, and the importance of 13 this factor on photosynthetic rate variability throughout the year and under regular 14 cropping conditions. The photosynthetic rate was measured on 60 days throughout the 15 year on field-grown sweet orange plants under natural conditions in the Valencian 16 Community, the most important citrus-producing area of Spain. The experiments were 17 performed on the "on" (high crop) and "off" (low crop) bearing 40-year-old Salustiana 18 sweet orange trees growing in the same orchard. Gas exchange and fluorescence 19 parameters were measured during the year in young and old leaves on sun-exposed 20 branches with and without fruit in the "on" trees, and in fruitless branches of the "off" 21 trees. In non-manipulated Citrus trees, fruit load has no significant effect in any season 22 on the photosynthetic rate in the leaves from branches without fruit. However, in high 23 crop trees, the leaves of branches bearing fruit present a sl...
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