Embryogenic response from anther culture of cultivars of loquat (Eriobotrya japonica (Thunb.) Lindl.) from different origins
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Homozygous lines are very interesting for genetic studies and in plant breeding. These can be produced in a single step via haploidy. Production of haploids in loquat (Eriobotrya japonica (Thunb.) Lindl.) would be of considerable value. In this study, androgenesis by anther culture was used to regenerate loquat plants. Different variables related to the induction of embryogenesis were tested, including the temperature pretreatment of flower buds, various levels of growth regulators in the culture medium, and genotypic effects. Eight cultivars of loquat from different geographic origins were used. The first step, the association between floral bud size and the corresponding microspore/pollen developmental stages was established for the different cultivars. Bud sizes of 6.5-7.0 mm, corresponded to the uninucleate microspore stage and provided the highest callogenesis levels. Pre-treatment of flower buds at 4 A degrees C for had a negative effect on anther response and only the 4-day pre-treatment resulted in callus formation at all. The highest percentage of morphogenetic calli was obtained on medium supplemented with 4.56 mu M zeatin (Z) and 5.36 mu M 1_naphthalene acetic acid (NAA) in cvs. 'Changhong-3' (27 %), 'Jiefanghong' (30 %) and 'Moggi Wase' (36 %). Following a transfer of morphogenetic calli to the embryo induction medium, six embryos were obtained from cv. 'Jiefanghong'; and one of them developed into a plantlet. Flow cytometry and chromosome counts revealed that the plantlet was triploid. The single triploid plant obtained was unexpected and its origin is obscure. One possible explanation is that it arose from fusion of sperm nucleus and two vegetative nuclei.