Influence of micropropagation through somatic embryogenesis on somaclonal variation in coffee (Coffea arabica) : assessment of variations at the phenotypical, cytological, genetic and epigenetic level

• Main Author: Bobadilla Landey, Roberto
• Language: English
• Published: Université Montpellier II - Sciences et Techniques du Languedoc 2013
• Subjects: [SDV:BV] Life Sciences/Vegetal Biology; [SDV:BV] Sciences du Vivant/Biologie végétale; Somatic embryogenesis; Coffee; Genome
• Online Access: http://tel.archives-ouvertes.fr/tel-01016417; http://tel.archives-ouvertes.fr/docs/01/01/64/17/PDF/33355_BOBADILLA-3_cor.pdf

Influence of micropropagation through somatic embryogenesis on somaclonal variation in coffee (Coffea arabica): assessment of variations at the phenotypical, cytological, genetic and epigenetic level Somaclonal variation (SV) is a major concern in all micropropagation systems. It is described as the phenotypic variation displayed in in vitro-derived regenerants and it is believed to be originated from a large array of genetic and epigenetic mechanisms. Highly productive Coffea arabica hybrids are clonally disseminated in Meso-American region through somatic embryogenesis (SE). The objective of the present work in coffee is to evaluate the trueness-to-type of SE and to understand the mechanisms involved in SV. We assessed the variations in the propagated plants at the phenotypic, cytogenetic, genetic (mutations/AFLP, genetic transposition/S-SAP) and epigenetic (methylation/MSAP) level by using two complementary approaches. First, with 2 hybrids we studied industrial culture conditions expected to be weakly mutagenic thanks to the combined use of short term proliferation period (6 months) and low auxin supply (0-1.4 µM 2,4-D). Two proliferation systems i.e. secondary embryogenesis and embryogenic suspensions were compared, the latter being more productive and economic. AFLP and MSAP molecular analyses on 145 somatic seedlings showed that genetic and epigenetic polymorphisms between mother plants and emblings were extremely low, i.e. ranges of 0-0.003% and 0.07-0.18% respectively, with no significant difference between the proliferation systems. For the two hybrids tested, massive phenotypic observations in nursery and field plots showed very low levels of SV (0.9% from 800,000 plants). Cytological analysis showed abnormal chromosome numbers (41-43, 45) in most of coffee somaclonal variants and normal numbers (44) in phenotypically normal plants. Stressful experimental conditions were also applied by using extended proliferation periods (4, 12 and 27 months) for three independent embryogenic lines established for the Caturra var. in presence of high growth regulator concentrations (4.5 μM 2,4-D, 17.8 μM 6-BA) to understand the mechanisms of culture ageing on SV. The proliferation time strongly affected the SV frequency among the 180 regenerated plants and in a highly similar way with the three embryogenic lines. No variant was found after 4 months proliferation although 30% and 94% phenotypic variants were observed in plants derived from 12 and 27 month-old cultures, respectively. Regardless the culture age and the embryogenic line, no polymorphisms were found in the 124 plants analyzed and very limited methylation changes with MSAP markers (0.049-0.087%). However, similarly to plants derived from industrial conditions, phenotypic variants systematically showed abnormal chromosome numbers and normal plants systematically showed normal numbers. This work showed that SE based on embryogenic suspensions is reliable for true-to-type propagation of selected C. arabica varieties. It also demonstrated the importance of culture age on SV and hence the non random nature of this phenomenon. The genetic and epigenetic alterations are particularly limited during SE. The main change in most of phenotypic variants was aneuploidy showing that mitotic aberrations play a major role in SV in coffee.