Colchicine-induced polyploidy in loquat (Eriobotrya japonica (Thunb.) Lindl.)
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The induction of polyploids in loquat (Eriobotrya japonica (Thunb.) Lindl.) is of great interest for producing larger and seedless fruits according to market demands. Under this premise, this work was aimed to obtain tetraploid plants of loquat using the antimitotic agent colchicine. Experiments consisted in applying colchicine on shoot apex from in vitro-grown plants, in vitro-grown whole plants and ungerminated seeds. Treatments on the shoot apex or submerging whole plants produced no stable polyploids. Conversely, subjecting ungerminated seeds to colchicine produced two triploids in the 0.5 % (w/v) solution after 24 h and one tetraploid after 48 h. The triploids obtained among treated seeds make us believe that these plants were present in the hybrids original seedlot. Polyploidy levels were firstly detected by flow cytometry and later confirmed by chromosome counting and morphological characteristics. The relative fluorescence was 1.5-fold higher in triploids and twofold higher in tetraploids as compared to diploids. As expected, the chromosome number was 2n = 34 in diploids, 2n = 51 in triploids and 2n = 68 in the tetraploid. Moreover, differences in morphological characteristics between diploid and polyploid plants were significant. The tetraploid plant was more compact than triploids or diploids. Particularly, stomata of polyploids were larger with lower density than diploids. Results indicate that induction of polyploidy in loquat species is a reliable tool for breeding new loquat varieties.