Poliembrionia e potencial de obtenção de híbridos em citros

Abstract

A ocorrência de poliembrionia, elevada heterozigosidade e longo período pré-reprodutivo são os principais obstáculos à geração de variedades híbridas de citros. Este trabalho teve como objetivo a obtenção de indivíduos com potencial de uso como porta-enxertos através de cruzamentos entre diversas variedades. Observou-se que as hibridações envolvendo a tangerineira 'Sunki da Flórida' (TSKFL) como parental feminino possibilitaram a geração de maiores quantidades de híbridos, dando-se o contrário em relação àquelas em que os parentais femininos foram as tangerineiras 'Cleópatra', 'Sunki Maravilha', 'Sunki Tropical' e 'Dancy', assim como o limeiro 'Rugoso da Flórida', ocupando posições intermediárias os limoeiros 'Cravo Santa Cruz' e 'Rugoso CNPMF-001'. Confrontando essas observações com as relativas ao grau de poliembrionia dos parentais femininos utilizados, constatou-se, de modo geral, uma relação inversa entre o grau de poliembrionia e o número de híbridos gerados. Os cruzamentos TSKFL x (limoeiro 'Cravo x Poncirus trifolata), TSKFL x citrange 'Yuma', TSKFL x citrangequat 'Thomasville', TSKFL x Citrus webberi, TSKFL x citrange 'Argentina' e TSKFL x citrange 'Coleman', notadamente os quatro primeiros, permitiram a obtenção de elevadas quantidades de híbridos.

Water deficit increases the frequency of hybrid citrus with polyembryonic female parents

“…Soares Filho et al (2014) demonstrated that the degree of polyembryony is inversely proportional to the number of hybrids formed from controlled crosses. This demonstration was based on the results of crosses involving female parents with different degrees of polyembryony, which ranged from 8% to nearly 100% in 'Sunki Florida' mandarin, as verified in the following mandarins: 'Sunki Tropical' (94 %), 'Sunki Maravilha' (97%), 'Cleopatra' (98%) and 'Dancy' (99%) (C. tangerina Tanaka).…”

“…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.…”

“…The good performance of hybrid rootstocks generated from crosses with P. trifoliata can not only produce stable and productive orchards but also enable their expansion into non-producing regions, with positive effects on the income of growers. In addition, hybridizations with P. trifoliata are routine because this species is associated with a dominant, readily evident, morphological marker, which is the presence of leaves with trifoliate blades, allowing the early identification of zygotic seedlings derived from crosses with female parents whose leaf blades are simple (Soares Filho et al 2014). …”

“…The process of obtaining hybrids is restricted by the high polyembryony of certain female parents, the high heterozygosity that is common to most citrus species, and the long period needed to assess the generated individuals (Soares Filho et al 2014). Referring to polyembryony, the presence of many nucellar embryos in the same seed and their subsequent competition with the zygotic embryo hinder the survival of the zygotic embryo and may lead to the elimination of individuals with potential for agronomical use.…”

“…ex Tanaka] Tropical selection, whose polyembryony approaches 100%, unlike the common 'Sunki', which presents a low degree of polyembryony, less than 20% (Soares Filho et al 2002). This situation limits the recovery of hybrids (Soares Filho et al 2014) and thereby constructs a barrier to the development of new rootstocks.…”