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  • Author or Editor: Zhiqin Zhou x
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Citrus species are among the most important fruit trees in the world and have a long cultivation history. However, until now, the exact genetic origins of cultivated Citrus such as sweet orange (Citrus sinensis), lemon (C. limon), and grapefruit (C. paradisi) have remained unidentified. In the present study, amplified fragment length polymorphism (AFLP) fingerprints, nuclear internal transcribed spacer (ITS), and three plastid DNA regions (psbH – petB, trnL – trnF, and trnS - trnG) of 30 accessions of the cultivated citrus and their putative wild ancestors were analyzed in an attempt to identify their paternal and maternal origins. Molecular phylogenetic trees were constructed based on the AFLP data, and chloroplast DNA and ITS sequences using the genus Poncirus as the outgroup. Our results indicated that bergamot (C. aurantifolia) and lemon were derived from citron (C. medica) and sour orange (C. aurantium), and grapefruit was a hybrid that originated from a cross between pummelo (C. grandis) and sweet orange. Rough lemon (C. limon) was probable as a parent of rangpur lime (C. limonia) and guangxi local lemon (C. limonia). Our data also demonstrated that sweet orange and sour orange were hybrids of mandarin (C. reticulata) and pummelo, while rough lemon was a cross between citron and mandarin. For mexican lime (C. aurantifolia), our molecular data confirmed a species of Papeda to be the female parent and C. medica as the male. These findings provide new information for future study on the taxonomy, evolution, and genetic breeding of Citrus.

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Dwarfing rootstocks can improve the plant architecture of apple trees and increase production. Gibberellins (GAs) are crucial for plant growth and dwarfing traits. The receptor, GIBBERELLIN INSENSITIVE DWARF1 (GID1), plays an important role in the regulation pathway. However, the growth regulatory mechanism of GID1 in dwarf apple rootstock seedlings is not clear. In this study, we selected dwarf apple rootstock ‘SH6’ and its cross parents as materials to clone the GA receptor gene GID1c. There were two different sites in the alpha/beta hydrolase domain. The expression of GID1c in ‘SH6’ was lower than that in Malus domestica cv. Ralls Janet, with the decrease of GA content. We further conducted GA3 treatment and overexpression of GID1c in tissue culture seedlings of ‘SH6’, and the results showed that the expression of GID1c and biosynthesis genes increased and promoted the accumulation of hormone contents, which ultimately regulates the growth of ‘SH6’ dwarf apple rootstock seedlings. Our results suggest that GID1c may affect the plant architecture and dwarf traits of dwarfing rootstock and accelerate its application in orchards.

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