Abstract
Abstract The aim of this study was to develop a methodology that uses water deficit induction to increase the frequency of hybrids in Citrus varieties that have a high and an intermediate level of polyembryony, respectively. The experiment examined the ‘Sunki Tropical’ mandarin and ‘Rangpur Santa Cruz’ lime genotypes at three water stress intensities: 20, 40 and 100% of the pot capacity (PC). The generated fruits were harvested, and the seeds were counted. After germination, the number of nucellar and hybrid seedlings was determined. For ‘Rangpur Santa Cruz’ lime genotype, the highest hybrid frequency generated was 64.2%, which occurred at a PC of 40% and exceeded by 12% that occurring at a PC of 100%. For ‘Sunki Tropical’ mandarin, the highest observed hybrid frequency was 21.75%, which occurred at a PC of 20% and was more than double the hybrid frequency of 8.57% observed at 100% of the PC.
Highlights
Most plant species are perpetuated by zygotic embryogenesis, but some, such as citrus, are able to spread naturally from somatic cells, a phenomenon called apomixis (Nakano et al 2013) and by rooting of stem cuttings, keeping, in both cases, genotypic characteristics of the original plant (Siviero et al 2003)
These varieties, which are commercially used as rootstocks for citrus growers, were grafted onto hybrid CSM x (RL x PT) - 059, where CSM refers to the common ‘Sunki’ mandarin, RL to ‘Rangpur’ lime and PT to the species P. trifoliata
When compared with the control treatment (100% of the pot capacity (PC)), an increase of the greatest magnitude in fruit number and, in the amount of available seed was observed in both genotypes for the most severe water deficit treatment, the 20% of PC treatment, followed by lesser increases for the 40% of PC treatment
Summary
Most plant species are perpetuated by zygotic embryogenesis, but some, such as citrus, are able to spread naturally from somatic cells, a phenomenon called apomixis (Nakano et al 2013) and by rooting of stem cuttings, keeping, in both cases, genotypic characteristics of the original plant (Siviero et al 2003). Polyembryony is a type of apomictic reproduction that is responsible for generating more than one embryo per seed (Chen et al 2008, Soares Filho et al 2014). This peculiarity allows the multiplication of interesting genotypes, especially in the case of rootstocks, by generating clones formed from the nucellar tissue of the mother plant. Among the solutions is the diversification of rootstocks, especially those from crosses with Poncirus trifoliata (L.) Raf., an important species in the development of new varieties because of their tolerance to certain biotic stresses (Ollitrault and Navarro 2012).
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