François-Xavier Côte

Comparison of methods of liquid medium culture for banana micropropagation : effects of temporary immersion of explants

AbstractFive different liquid medium culture methods for meristem propagation of bananas were investigated and compared with solid medium culture. Treatments studied were: gelled culture medium (treatment 1); liquid medium with immersion of the plants (treatment 2); liquid medium with cellulose culture support (treatment 3); liquid medium with partial immersion of the plants (treatment 4); liquid medium aerated by bubbling (treatment 5); liquid medium with temporary immersion of the explants for 20 min every 2h (treatment 6). After 20 days of culture, three culture groups with statistically different multiplication rates were observed:-shoots in simple liquid medium and those on cellulose substrate proliferated little or not at all,-shoots on gelled medium, those subjected to partial immersion and those in aerated medium displayed multiplication rates of 2.2 to 3.1, and-the highest multiplication rate (>5) was observed in explants subjected to temporary immersion in the medium. Two groups of treatments differed in the accumulation of dry matter: the smallest weight (around 0.5 g) was observed in treatment 1, 2, 3 and 4, and accumulation was 2 to 5 times greater in the explants in aerated liquid medium and those subjected to temporary immersion. The highest multiplication rates and weight gains were observed in aerated treatments (treatments 4 and 5). Shoots in liquid medium continuously aerated by bubbling displayed hyperhydricity of the outer leaf sheaths. This was not observed with temporary immersion of explants.

Amplified somatic embryogenesis from male flowers of triploid banana and plantain cultivars (Musa spp.)

SummarySomatic embryogenesis and plant regeneration of banana and plantain cultivars (Musa spp.) were obtained by culturing young male flowers. Multiplication and maintenance of embryogenic cultures were achieved by culturing somatic embryos in a temporary immersion system (SIT). A multiplication rate of 40 allowed us to obtain more than 6000 somatic embryos after 6 mo. of subculture. Plant recovery frequencies were 60 to 70%. This method was expanded to different banana and plantain genomic groups.

Influence of donor material and genotype on protoplast regeneration in banana and plantain cultivars (#Musa# spp.)

Among the various strategies for genetic improvement in banana, somatic hybridisation appears to be a promising complement to classical breeding since protoplasts are amenable to plant regeneration. Therefore, the present investigation was undertaken to improve protoplast regeneration in banana. Protoplasts were isolated from young leaves, calli and embryogenic cell suspensions. The highest protoplast yield was obtained with cell suspensions. Mesophyll protoplasts and callus-derived protoplasts did not divide. However, protoplasts isolated from cell suspension developed into plants. Feeder cells and protoplast culture at high density were required for plant regeneration from protoplasts. Plant regeneration through somatic embryogenesis was achieved in Grande Naine and Gros Michel (Musa spp. Sub-Group cavendish AAA), Currare Enano and Dominico (Sub-Group plantain AAB), SF265, IRFA903 and Col49 (Sub-Group AA). The frequency of embryo formation and plant regeneration was genotype-dependent. Large number of somatic embryos and regenerated plants were produced in SF265 (AA) followed by Dominico (AAB) and Grande Naine (AAA).

Morphohistological study of the different constituents of a banana (Musa 'AAA', cv. 'Grande Naine') embryogenic cell suspension

Abstract Five types of cellular aggregates have been characterised in embryogenic cell suspensions of banana (Musa AAA Grande naine cv.). Type I corresponded to isolated cells or to small cell aggregates. Type II were composed of embryogenic cells. Type III can be distinguished from type II due to the presence of peripheral proliferation zones with embryonic cells. Type IV were composed of protodermic masses histologically comparable to proembryos. Type V were nodules composed of a central zone of meristematic cells and of an external zone of starchy cells. Each culture flask of a cell line contained a majority of one of the above-mentioned aggregate types. Histological studies of somatic embryo developement on semi-solid regeneration medium showed that there were close similarities between the initial steps of ontogenesis of the embryos and the different cell aggregates in liquid multiplication medium. It appeared that aggregates II–IV of the suspension belong to the same development continuum which reproduces the initial phases of somatic embryo ontogenesis on semi-solid medium. Type V resulted from the development of type IV, for which ontogenesis is hindered by direct contact with 2,4-dichlorophenoxyacetic acid and the shaken liquid multiplication medium. Type I aggregates probably do not belong to the development continuum but rather correspond to the degeneration of the other types of aggregates in the suspension. The presence of intermediate types in the liquid medium reinforces the hypothesis of a relationship between the aggregates. The aggregates tended to develop through time from a majority of type II or III at the beginning of their culture to types IV–V for older suspensions.

Somaclonal variation rate evolution in plant tissue culture: Contribution to understanding through a statistical approach

SummaryIn order to better understand somaclonal variant rate evolution in plant tissue culture, a statistical approach has been adopted. According to this approach, the variant percentage could be calculated by: %V=[1−(1−p)n]×100, where %V is the percentage of variant, p the probability of variation and n the number of multiplication cycles. A numerical estimation was performed to characterize the variance of this function. It has been demonstrated that a wide scale of variance is associated with ‘%V’, due to the occurrence of variations after a variable number of multiplication cycles in the different lines of culture. Two main conclusions can be drawn from this model: (1) a variant rate increase can be expected as an exponential function of the number of multiplication cycles; (2) after a given number of multiplication cycles, variable off-types percentages can be expected. Due to the complexity of biological systems, this statistical approach could obviously not be applied directly for the calculation and forecasting of variant rates in tissue culture. However, this approach results in a better understanding of two apparently confusing experimental features often reported in tissue culture: the increase of the variant rate as a function of the length of the culture period on the one hand, and, on the other hand, the observations of different variant rates among lines cultured for the same lengths of time under strietly identical culture conditions. This approach also underlined that the comparison of somaclonal variant percentage between batches of plants from different in vitro treatments could be, in some cases, insufficient for ascertaining a difference of variability generated by tissue culture.

Chromosome number variations in micropropagated true-to-type and off-type banana plants (Musa AAA Grande Naine cv.)

SummaryThe objective of the present study on banana plants (Musa AAA Grande Naine cv.), obtained byin vitro shoot tip culture, was to determine whether modifications in chromosome number could account for the appearance of the off-types with mosaiclike leaf defects or dwarf stature, the most frequent off-types observed after micropropagation. Chromosome counts were conducted on shoot tip samples treated with 8-hydroxyquinoline, digested in pectinase and stained with Schiffs reagent. On average, 160 counts were made for each treatment. Four types of plant material were studied: phenotypically true-to-type plants, dwarf off types, mosaiclike off-types obtained by micropropagation, as well as true-to-type plants obtained by standard propagation techniques of suckers with no micropropagation history. Some cells from all four types of plant material were found to have an abnormal chromosome number (i.e., 2n = 3x = 33), characteristic of triploid banarias. The percentages of aneuploid cells were 14%, 22%, 35%, and 5%, respectively. Descending aneuploidy was noted in micropropagated plants derived from true-to-type and dwarf off-type suckers. The statistical analysis revealed that the two latter types of plant material had the same percentage of aneuploid cells. Thus, the dwarfism could not be correlated with a change in the chromosome number. Conversely, ascending aneuploidy was observed in the mosaiclike material, with 34 or 35 chromosomes in almost 28% of the cells. This percentage was significantly higher than in true-to-type plants and highlight the genetic origin of the mosaiclike variation.

Micropropagation of Musa Species (Bananas)

The use of planting material obtained by in vitro micropropagation is certainly the most significant advance in banana cultivation techniques in the past decade. Vitroplants, which were almost unknown at the beginning of the 1980s, are now widely used in Latin America, the Caribbean, the Pacific rim, and in Africa.