Regeneration of Allotriploid Coffea Plants from Tissue Culture: Resolving the Propagation Problems Promoted by Irregular Meiosis

Abstract

“Híbrido de Timor” (HT) is a natural interspecific hybrid of Coffea arabica L. with Coffea canephora Pierre ex Froehner that has played a substantial role in breeding programs as source of resistance genes. The original HT plant is represented by the anorthoploid accession ‘CIFC 4106’, an allotriploid plant with 3x=33 chromosomes and 2C=2.10 pg. From this HT plant, other accessions have been obtained and used in crossings with C. arabica to provide resistant plants to the main pathogens. However, each HT accession and their derivates show a particular karyotype due to irregular anaphasic disjunction, which results in a few reproductive cells with an unbalanced number of chromosomes. Regarding this fact and the crop relevance of HT, this study aimed to develop a direct somatic embryogenesis system for the clonal propagation of this germplasm, using the first HT plant as explant donor. To accomplish this purpose, disinfested leaf explants of greenhouse-cultivated HT ‘CIFC 4106’ plants were inoculated in medium supplied with 0.001 g L⁻¹ 6-benzylaminopurine. Somatic embryogenesis process was asynchronous, with distinct developmental stages occurring simultaneously. Besides, emergence of secondary embryos from primary ones was observed. Mature embryos were germinated, and well-rooted embryos were selected for plantlet regeneration. The nuclear DNA content and the karyotype showed that allotriploidy was conserved in all regenerated plantlets. Considering these results, the direct somatic embryogenesis protocol adopted in the present work was imperative for the accurate clonal propagation of HT, being relevant for multiplication and conservation of elite accessions that show an irregular meiosis.