Estimating the cost of flowering in a grapefruit tree

Abstract

The objective of the present study is to evaluate a Citrus tree's investment in the flowering process in relation to its photoassimilate resources, as a part of its annual reproductive effort. The overall requirement for carbohydrate of a single flower of grapefruit (Citrus paradisi Macf. cv. 'Marsh seedless') is evaluated as 8·33 × 10 -3 mol C over 3 weeks. The direct cost of production of a single flower is estimated to be 5·75 × 10 -3 mol C, most of which is allocated to the petals, anthers and style -organs designated to abscise. About 2·58 × 10 -3 mol C is consumed by respiration not associated with growth processes. Growth respiration (R g ) occurs mostly during early stages of flower growth and development. However, the total respiration rate increases sharply during anthesis, when growth processes have almost ceased. Ethylene evolution also reaches remarkably high rates during anthesis. High temperatures increase the rate of flower respiration (Q 10 = 2·12) but shorten the duration of flowering. A grapefruit tree may bear each year 20 000-50 000 flowers, only 0·5-2·5% of which develop into mature fruit. The amount of carbohydrate invested each year in bloom at the whole-tree level is 166-400 mol C per tree (depending on the number of flowers), amounting to 10-20% of the carbohydrate consumed for fruit growth. The overall daily demand for carbohydrate by the flowers of a grapefruit tree during anthesis may exceed the daily carbohydrate production by the leaves. High temperatures lead to a further increase in the daily demand for carbohydrate. In such cases, the management of flowering must rely on carbohydrate reserves recruited from other tree organs. The ecophysiological and evolutionary aspects of Citrus flowering are discussed.Key-words: Citrus paradisi; alternative pathway of respiration; carbohydrate demand; flowering; growth respiration; maintenance respiration; reproductive effort; sink; source. INTRODUCTIONA single Citrus tree (e.g. C. sinensis) may bear a large number of flowers (up to 250 000) during each blooming season, depending on the cultivar, tree size and environmental conditions (Monselise 1986). Only a small proportion of the flowers develop into mature fruit (0·1-3·5%) (Monselise 1986); most of the reproductive units abscise as flowers or fruitlets within 2 months of blooming. A grapefruit (C. paradisi) tree bears a relatively modest number of flowers, 20 000-50 000, only 400-600 of which will be harvested as fruit.Citrus flower development lasts about 3-5 weeks and may be characterized by several stages (Goldschmidt & Huberman 1974), as illustrated in Fig. 1. At anthesis, growth (in terms of dry weight) of all flower organs except the ovary has already terminated. Petals, anthers and style, which comprise the larger portion of the flower, drop after anthesis. Considerable nectar production (Monselise 1985) and respiratory losses must also be taken into account in the metabolic cost of flowering.Weather conditions during bloom, mainly temperature, have major effects on Citrus ...

Physiology of citrus fruiting

“…IGLESIAS et al resources. For some authors, however, this reproductive pattern may be linked to a survival strategy (Bustan and Goldschmidt, 1998).…”

Response of the photosynthetic apparatus to a flowering-inductive period by water stress in Citrus

“…After reserves have been depleted during bud sprouting and flowering, fruit development is supported by current photosynthesis (Bustan and Goldschmidt 1998). Although flower and vegetative shoot formation was induced by a drought period in both studied species, the effect of water stress on the photosynthetic integrity and recovery after rehydration has to be assessed in order to improve resource efficiency.…”

Carboidratos foliares durante a floração e os estádios iniciais de crescimento de frutilhos em tangerineira 'Ponkan'

“…de reservas para a formação e o desenvolvimento de flores e frutos (Bolding et al, 2003;Cruz et al, 2007), uma vez que a produção diária de carboidratos pelas plantas não atende à demanda total nessas fases (Bustan & Goldschmidt, 1998). Portanto, práticas de manejo que proporcionem a manutenção das reservas de carboidratos nas tangerineiras 'Ponkan' são importantes para promover floração no ano seguinte e para o desenvolvimento de frutos com qualidade adequada.…”