The genome of Musa balbisiana spp. contains several infectious endogenous sequences of Banana streak virus (eBSV). We have shown previously that in vitro micropropagation triggers the activation of infectious eBSOLV (endogenous sequences of Banana streak Obino l'Ewai virus) in the synthetic tetraploid interspecific hybrid FHIA21 (AAAB). In this work, we show that another synthetic tetraploid (AAAB) hybrid and two natural triploid (AAB) plantains are equally prone to the activation of infectious eBSOLV during tissue culture. These results are a strong indication that such activation is a general phenomenon in interspecific Musa cultivars, whether synthetic or natural. We also report the first in-depth study of the correlation between the duration of tissue culture and the level of activation of infectious eBSOLV, and show that specific and common activation patterns exist in these banana plants. We hypothesize that these patterns result from the concomitant activation of infectious eBSOLV and a decrease in the virus titre in neoformed plantlets, resulting from cell multiplication outcompeting virus replication. We provide experimental data supporting this hypothesis. No activation of infectious eBSGFV (endogenous sequences of Banana streak Goldfinger virus) by tissue culture was observed in the two natural AAB plantain cultivars studied here, whereas such activation occurred in the AAAB synthetic hybrid studied. We demonstrate that this differential activation does not result from differences in the structure of eBSGFV, as all banana genomes harbour eaBSGFV-7.
Photosynthesis and light 02-uptake of the aerial portion of the CAM plant Ananas comosus (L.) meff. were studied by C02 and 02 gas exchange measurements. The amount of C02 which was fixed during a complete day-night cycle was equal to the amount of total net 02 evolved. This finding justifies the assumption that in each time interval of the light period, the difference between the rates of net 02-evolution and of net light atmospheric C02-uptake give the rates of malate-decarboxylation-dependent C02 assimilation. Based upon this hypothesis, the following photosynthetic characteristics were observed: (a) From the onset of the light to midphase IV of CAM, the photosynthetic quotient (net 02 evolved/net C02 fixed) was higher than 1. This indicates that malate-decarboxylation supplied C02 for the photosynthetic carbon reduction cycle during this period. (b) In phase IlIl and early phase IV, the rate of C02 assimilation deduced from net 02-evolution was 3 times higher than the maximum rate of atmospheric C02-fixation during phase IV. A conceivable explanation for this stimulation of photosynthesis is that the intracellular C02-concentration was high because of malate decarboxylation. (c) During the final hours of the light period, the photosynthetic quotient decreased below 1. This may be the result of C02-fixation by phosphoenolpyruvate-carboxylase activity and malate accumulation. Based upon this hypothesis, the gas exchange data indicates that at least 50% of the C02 fixed during the last hour of the light period was stored as malate. Light 02-uptake determined with 1802 showed two remarkable characteristics: from the onset of the light until midphase IV the rate of 02-uptake increased progressively; during the following part of the light period, the rate of 02-uptake was 3.5 times higher than the maximum rate of C02-uptake. When malate decarboxylation was reduced or suppressed after a night in a C02-free atmosphere or in continuous illumination, the rate of 02-uptake was higher than in the control. This supports the hypothesis that the low rate of 02-uptake in the first part of the light period is due to the inhibition of photorespiration by increased intracellular CO2 concentration because of malate decarboxylation. In view of the law of gas diffusion and the kinetic properties of the ribulose-1,5-bisphosphate carboxylase/oxygenase, 02 and C02 gas exchange suggest that at the end of the light period the intracellular CO2 concentration was very low. We propose that the high ratio of 02-uptake/C02-fixation is principally caused by the stimulation of photorespiration during this period.Crassulacean acid metabolism affords a mechanism for the temporal separation ofC02-fixation and C02-reduction. During the dark period, PEP-Case' catalyses the fixation of CO2 and malate is formed. During the light period, CO2 is released from malate decarboxylation. This CO2 is fixed by Rubisco and assimilated in the PCR (in this paper, the term C02-assimilation means C02-reduction in the PCR). Atmospheric C02-uptake is also ...
Comparison of the effectiveness of two vegetative propagation methods for banana trees from the study of the agronomic characteristics of a hybrid of plantain (Musa spp.). Abstract-Introduction. The objective of our study was to evaluate the agronomic performance of plantain hybrid plants (CRBP-39, Musa cv. AAAB) obtained through two vegetative propagation methods: in vitro culture, called the "CIV technique", and a newly developed technique of plants derived from stem bits, called the "PIF technique". The study, carried out in Cameroon, took place at a high altitude (1250 m) and covered one cropping cycle. The CRBP-39 hybrid was chosen because of its resistance to Black Leaf Streak Disease and its agronomic performance. Materials and methods. Vitroplants and plants obtained through the PIF technique developed at CARBAP (Cameroon) were planted separately in elementary plots of 16 plants. No chemical control was administered against Black Leaf Streak Disease. Observations were essentially made on agronomic characteristics. Results and discussion. For the mother crop, there was no significant difference between the plants obtained from one or the other vegetative propagation method concerning their pseudo-stem height and girth; the number of functional leaves at shooting; the duration of the production cycle; the bunch weight; the number of hands and fruits of the bunch; and the length and circumference of the fruit. For the ratoon crop, significant differences were observed concerning the pseudo-stem height and girth, and the number of emitted and functional leaves at harvest. These results globally indicate a strong similarity in vegetative and bunch characteristics of plants propagated with one or the other method. The PIF technique, which is used more and more by small-scale farmers because of its simplicity, rapidness and low cost of production, is a method of vegetative propagation that helps to produce plants similar to tissue cultured plants in terms of agronomic qualities. Cameroon / Musa (plantains) / hybrids / plant propagation / vitroplants / propagation materials Comparaison de l'efficacité de deux méthodes de multiplication rapide de plants de bananier à partir de l'étude des caractéristiques agronomiques d'un hybride de bananier plantain (Musa spp.). Résumé-Introduction. Nos travaux ont eu pour objectif de comparer les performances agronomiques des plants d'un hybride de bananier plantain (CRBP-39, Musa cv. AAAB) obtenus par utilisation de deux méthodes de multiplication végétative : la culture de tissus in vitro (CIV) et une technique de propagation par multiplication de plants à partir de fragments de tiges (dite technique des PIF) développée récemment. L'étude, effectuée au Cameroun, a été menée en altitude (1250 m) ; elle a porté sur un cycle de culture. L'hybride CRBP-39 a été choisi en raison de sa résistance à la maladie des raies noires et de ses performances agronomiques. Matériel et méthodes. Des vitroplants et des plants obtenus par la technique des PIF, technique de propagation horticole ...
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