Musa AAA Cv Research Articles

Endogenous phytohormone analysis during sequential stages of somatic embryogenesis in Musa AAA cv. Grand Naine (subgroup Cavendish)

Abstract This is the first initiative study to provide quantified levels of four endogenous phytohormones during the induction, regeneration, maturation and germination stages of somatic embryogenesis (SE) in banana, using immature male bud explants, in the popular commercial triploid cultivar Grand Naine (AAA). Phytohormones are known to play a major role in the regulation of SE and most protocols have been developed for various cultivars of banana following empirical approaches. Although, several reports are available with regard to the impact of growth regulators exogenously supplemented to the media, the vital role of endogenous growth hormones in various developmental stages of SE remain unclear in banana. Reverse Phase High Performance Liquid Chromatography (RP-HPLC) was used to analyze endogenous status of indole acetic acid (IAA), zeatin, gibberellic acid (GA) and abscisic acid (ABA). Results from this study revealed that endogenous IAA and GA along with exogenous auxin play a major role in the induction of embryogenic competence of male bud explants. The levels of endogenous IAA and zeatin were found to be higher in embryogenic calli than non-embryogenic calli, although three different types of exogenous auxins were supplemented in callogenesis medium, but not cytokinin. Higher level of ABA and GA was observed in early and late developmental stages of somatic embryo, respectively. GA also played a predominant role in germination of somatic embryos. These findings will be applied for improvement of SE protocol in recalcitrant banana cultivars by suitably altering or supplementing exogenous growth hormones.

Evaluation of Attractants in Handcrafted Traps for Capture of Lepidopterans in Banana (Musa AAA cv. Williams)

Introduction: Banana cultivation is considered the main agricultural sector in Ecuador, however, like any other agricultural crop, it is attacked by a diversity of pests, among which the presence of insects of the order Lepidoptera stands out; For this reason, the objective of the research was to evaluate the efficiency of attractants in artisanal traps for the capture of lepidopterans in banana crops (Musa AAA) as strategies within pest monitoring and control programs. Taking place on a farm with Commercial Bananas (BC) and Organic Bananas (BO). A completely randomized design was used; In each location, two types of traps (plastic gallon and plastic bag) and five food attractants (Ripe banana, Ripe banana + Banana essence, Ripe banana, Ripe banana + Banana essence and Sugar cane + Molasses) were installed. 198 specimens were captured in the BO and 190 in the BC. The captured species were identified as: Ascalapha odorata, Caligo illioneus, Caligo bellerophon, Cissia sp., Opsiphanes tamarindi, Thysania zenobia and Colubura dirce. According to the Simpson index, the BO has the highest value (0.64) compared to the BC (0.52). In both locations it was evident that the most frequent species was O. tamarindi; According to records, the population of this species increased over time, which is why it requires attention. The attractants that allowed the greatest capture were: ripe banana, ripe banana and banana + essence. Objective: The objective of this study was to investigate the efficiency of attractants in artisanal traps for the capture of lepidopterans in banana crops (Musa AAA) as strategies within insect - pest monitoring and control programs. Theoretical Framework: This topic presents the main concepts and theories that support the research. The attractants in artisanal traps for capturing lepidopterans in banana stand out, providing a solid basis to understand the context of the research. Method: The methodology adopted for this research comprises a completely randomized design. Data collection was carried out using traps in the field. Results and Discussion: The results obtained revealed that the most frequent species was O. tamarindi and according to the population records, this species increased over time, which is why it requires attention. In the discussion section, these results are contextualized in light of the theoretical framework, highlighting the implications and relationships identified. This section also considers possible discrepancies and limitations of the study. Originality/Value: This study contributes to the literature by using artisanal traps with food attractants. The relevance and value of this research is evidenced in the use of more sustainable practices for the management and control of insects - pests in the country's banana cultivation.

Transcriptome Profiling during Sequential Stages of Cryopreservation in Banana (Musa AAA cv Borjahaji) Shoot Meristem.

Cryopreservation approaches have been implemented in gene banks as a strategy to back up plant genetic resource collections that are vegetatively propagated. Different strategies have been employed to effectively cryopreserve plant tissue. There is little information on the cellular processes and molecular adjustments that confer resilience to the multiple stresses imposed during a cryoprotocol. In the present work, the cryobionomics of banana (Musa sp.), a non-model species, was investigated through the transcriptomic approach using RNA-Seq. Proliferating meristems of in vitro explants (Musa AAA cv 'Borjahaji') were cryopreserved using the droplet-vitrification technique. Transcriptome profiling analysis of eight cDNA libraries including the bio-replicates for T0 (stock cultures (control tissue), T1 (high sucrose pre-cultured), T2 (vitrification solution-treated) and T3 (liquid nitrogen-treated) meristem tissues was carried out. The raw reads obtained were mapped with a Musa acuminata reference genome sequence. A total of 70 differentially expressed genes (DEGs) comprising 34 upregulated and 36 downregulated were identified in all three phases as compared to control (T0). Among the significant DEGs (>log FC 2.0), during sequential steps, 79 in T1, 3 in T2 and the 4 in T3 were upregulated and 122 in T1, 5 in T2 and 9 in T3 were downregulated. Gene ontology (GO) enrichment analysis showed that these significant DEGs were involved in the upregulation of biological process (BP-170), cellular component (CC-10) and molecular function (MF-94) and downregulation of biological process (BP-61), cellular component (CC-3) and molecular function (MF-56). The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that DEGs were involved in the biosynthesis of secondary metabolites, glycolysis/gluconeogenesis, MAPK signaling, EIN 3-lke 1 protein, 3-ketoacy-CoA synthase 6-like, and fatty acid elongation during cryopreservation. For the first time, a comprehensive transcript profiling during four stages of cryopreservation in banana were carried out, which will pave the way for devising an effective cryopreservation protocol.

Reduction of banana (Musa AAA cv Grande Naine) leaf photosynthesis by Radopholus similis

Objective: to determine the effect of Radopholus similis on banana (Musa AAA cv. Grande Naine) leaf photosynthesis. Methodology and Results: Four experiments were carried out under lathhouse conditions. In vitro plants were sown in pot of 1.8 L volume containing a soil (sterilized or unsterilized) from a commercial banana farm. Experiment 1: four treatments were evaluated. The treatments consisted of plants on unsterilized and sterilized banana soil without and with the inoculation of 500 (506 ± 18) R. similis per pot. During the three measuring times (7 am, 10 am, and 1 pm), at 45 days after inoculation, the highest photosynthesis rate was observed in the plants free of nematodes and the lowest in those plants inoculated with R. similis. In the evaluation at 10 am a reduction of 46% (P= 0.0307) in the photosynthesis rate was found on plants inoculated with R. similis that were grown in the sterilized banana soil. In experiment II: five treatments were evaluated on sterilized banana soil. One treatment was non-inoculated (control) and in the others, each plant was inoculated 15 days after sowing with 500 (509 ± 21), 1000 (1049 ± 34), 1500 (1526 ± 39) or 2000 (2056 ± 67) R. similis. After 75 days of the inoculation, from the six photosynthesis evaluation times (6-7, 8- 9, and 10-11 am or 12-1, 1-2 and 2-3 pm) with exception of that at 2-3 pm, the highest photosynthesis rate was observed in the plants free of nematodes. Reductions in the photosynthesis rate with nematode inoculation varied between 12 and 36% at 6-7 am, between 13 and 57% at 8- 9 am, between 32 and 57% at 10-11 am, and between 16 and 65% at 12-1 pm, and between 13 and 47% at 1-2 pm. The photosynthesis rate decreased linearly as the number of R. similis inoculated increased in the evaluations of 8-9 (P= 0.0070) and 10-11 am (P= 0.0049) or 12-1 pm (P= 0.0048) and 1-2 pm (P= 0.0255). In experiment III: two treatments were evaluated in sterilized banana soil in which the plants of one treatment were inoculated 19 days after sowing with 1500 (1564 ± 49) R. similis and the others were the control. A photosynthetic light response curve was determined at 75 days after inoculation showing that the area under curve of the potential assimilation rate of the plants inoculated with R. similis was reduced (P= 0.0153) by 70% compared to non-inoculated plants. In experiment IV: three treatments were evaluated where the plants of two treatments were sown in sterilized banana soil. One treatment was inoculated with 2000 (2078 ± 63) R. similis per pot, 21 days after sowing, and the other had no inoculation. The remaining treatment was set up in Castillo et al., J. Appl. Biosci. Vol : 169, 2022 Reduction of banana (Musa AAA cv Grande Naine) leaf photosynthesis by Radopholus similis 17618 unsterilized soil without nematode inoculation. The net assimilation rate curve before nematode inoculation differed (P= 0.0072) among treatments. A reduction of 33% in the accumulated net assimilation rate across the sequence of light points (0-2200 µmol m-2 s -1 ) was evidenced on the plants cultivated on banana soil without sterilization, which was infected with residual R. similis on the soil. The net assimilation rate curve at 4 (P< 0.0001), 11 (P= 0.0340) and 25 (P= 0.0127) days after nematode inoculation was higher on the plants free of nematodes. Conclusion and Application of results: In the four experiments, the lowest photosynthetic rate was found in the plants infected by R. similis. This confirms that the infection or parasitism of banana roots by R. similis, independently of if there are obvious root and foliage symptoms, consistently it reduces their photosynthesis rate, which in a long term will reduce crop performance. Therefore, nematode population must be monitored during the crop cycle to apply control measures in time in order to prevent production losses. Keywords: banana, Musa AAA, nematodes, photosynthesis, Radopholus similis

Changes in the Metabolite Profile during Micropropagation of Normal and Somaclonal Variants of Banana Musa AAA cv. Williams

Micropropagation techniques allow the mass production of banana plants but can cause somaclonal variations such as dwarfism. Changes in the metabolite profile during micropropagation of normal (NP) and dwarf (DP) banana plants have not been described. Both, NPs and DPs of banana Musa AAA cv. Williams were micropropagated and the metabolite profile of vitroplants was assessed at the proliferation (PP), rooting (RP) and the second greenhouse-acclimatization (APII) phases of tissue culture. Metabolites from 10 DPs and 10 NPs meristems from each micropropagation phase were extracted and identified by gas chromatography coupled with mass spectrometry (GC-MS). Principal component analysis (PCA) and test of statistical significance were applied to detect differentially accumulated metabolites. The PCA showed a clear grouping of DPs separated from NPs in RP and APII. Among the differentially accumulated metabolites, various precursors of apoplast components including arabinose and galactose or deoxygalactose in both PP and RP, as well as mannose and fucose in APII were under-accumulated in DPs. Results suggest affected apoplast composition during micropropagation of DPs.

Role of Bacillus tequilensis EA-CB0015 cells and lipopeptides in the biological control of black Sigatoka disease

Black Sigatoka disease is a devastating fungal pathogen that affects banana crops worldwide and is caused by the ascomycete fungus Pseudocercospora fijiensis. In an effort to mitigate the environmental impacts of chemical fungicides, microbial biological control agents (MBCA) have been developed. However, a comprehensive understanding of the modes of action of these products are needed to enhance their efficacy under field conditions. Consequently, the functional role of different components of a Bacillus tequilensis EA-CB0015-based product was studied to understand their role in conferring protection to banana plants against the infection of P. fijiensis. Under this perspective, we evaluated the effect of B. tequilensis EA-CB0015 lipopetides on the severity of black Sigatoka disease, as well as the ability of the bacterial cells to colonize and produce lipopeptides on the leaf surface of banana plants (Musa AAA cv. Williams). Our work provides evidence that lipopetides significantly reduce the disease severity and that the bacterial cells colonize the leaf surface of banana plants inoculated with P. fijiensis during the first 48 h of incubation. Furthermore, we were able to detect an increased production of surfactins during colonization using mass spectrometry analysis. Altogether, our results suggest that the biological control strategies implemented by the MBCA product against P. fijiensis involves a direct interaction via antibiosis, as well as an indirect interaction via competition of nutrients and space.

Effect of nematicide rotation on banana (Musa AAA cv. Williams) root nematode control and crop yield

The effects of nematicide rotation on banana (Musa AAA cv. Williams) root weight, root nematode control, and crop yield were compared in a commercial banana plantation in Ecuador, testing six treatments in a randomized complete block design with six replicates. Treatments consisted of two, three and four different nematicide cycles per year plus the untreated control. Regarding the untreated plants and averaging the 24 root nematode samplings after treatment application, the nematicide applications reduced significantly R. similis (P<0.0001) between 20 and 49%, Helicotylenchus spp. (P<0.0001) between 31 and 51%, and total nematode populations (P<0.0001) between 29 and 49%. Accordingly, in the treated plants, there was an increase between 16 and 21% in living root weight (P=0.0003), and its percentage (P<0.0001) reached between 74.5 and 81.7% in the follower suckers. In addition, the death of roots by nematodes decreased (P=0.0009) between 20 and 46%. At harvest, nematicide applications increased bunch weight (P=0.0002; P=0.0467), ratio (P=0.0003 at 12 months), ratooning (P<0.0001; P<0.0001) and the number of boxes of 18.14 kg (P<0.0001; P=0.0005) per hectare per year at 12 and 24 months after treatment application, respectively. Plants treated with nematicides increased yield between 671 and 1,158 (12.2 - 21 t) and the number of boxes of 18.14 kg per hectare per year also increased between 545 and 1,046 (9.9 - 19.0 t), which resulted in a net profit between US $3,266 - $5,750 and between US $2,587 and $5,144 per hectare per year at 12 and 24 months after treatment application, respectively.

A new temporary immersion system for commercial micropropagation of banana (Musa AAA cv. Grand Naine)

Temporary immersion systems (TIS) are among the best options for commercial micropropagation. However, although successes have been reported with TIS, it is necessary to establish the most suitable system. The aim of this research was to compare the efficiency of different banana (Musa AAA cv. Grand Naine) micropropagation systems. In addition, a liquid medium with partial immersion and a semi-solid culture medium were evaluated. At 28 d of culture, the number and length of shoots, number of leaves per shoot, chlorophyll content, stomatal index, and the percentage of closed stomata were recorded. Additionally, the survival percentage and ex vitro development of the plantlets were evaluated during acclimatization. Results showed that TIS have a higher multiplication rate with respect to partial immersion and semi-solid medium. The chlorophyll content, stomatal index, and stomata functioning were affected by the different culture systems. The different culture systems had no effect on the survival percentage, although morphological differences were observed during acclimatization. The SETIS™ bioreactor was more efficient and resulted in better development in the plants obtained in vitro and ex vitro, which proved this system to be a useful alternative for banana micropropagation.

Chilling Prevention on Banana ‘Nanica’ in the Field with Bagging

Low temperature in the field causes chilling injury (CI) in banana and peel browning. The aim of this paper was to investigate the influence of different bagging materials and combinations on bunch development of banana (Musa AAA cv. Nanica) and the occurrence of CI. The study was carried in Jacupiranga, São Paulo, Brazil, in a completely randomized design in 2 × 9 factorial, two years of formation (2013 and 2014) and nine bagging materials, with eight replicates. Materials consisted in blue transparent polyethylene, white non-woven fabric, white opaque polyethylene, bubble wrap, white laminated non-woven fabric, double paper, blue transparent polyethylene plus kraft paper, blue transparent polyethylene plus white non-woven fabric and control (non-bagged). Fruits formed in both years showed low L* and C* values related to the CI index. On the coldest days of 2013 and 2014, bagging raised the temperature by only 1.91 and 3.17 °C, respectively. Depending on the year of bunch formation, the bagging materials influenced the period between flowering and harvest, but not the bunch mass. In the green fruit, the content of chlorophylls was lower in double paper, while L* was higher, but there were no differences in the content of phenols for the different materials. In mature fruits, CI index, L* and a* were not affected by the bagging materials, unlike coordinates b*, h° and C*, which were lower for double paper, with no difference between other materials and non-bagged fruits. Bagging materials did not prevent CI and did not reduce the peel browning intensity.

Effect of different nematicide applications per year on banana (Musa AAA) root nematode control and crop yield

Objective: The objective of this study was to evaluate the effect of different nematicide applications per year on control of banana root nematode, root weight and crop yield in Belize. The relationship between cost and benefit of the nematicide applications was also estimated. Methodology and results: A field experiment was conducted in a 40 years old commercial banana ( Musa AAA cv. Grande Naine) plantation from November 2011 to February 2013. Four treatments were evaluated: 1. Three nematicides (Nemacur ® , Mocap ® , Vydate ® ) applications per year with a 4-month interval, 2. Two nematicides (Nemacur ® , Mocap ® ) applications per year with a 6-month interval, 3. Nematicides applied based on nematode threshold (100 nematodes per g of fresh root) which resulted in two applications; Nemacur ® and Mocap ® with a 7-month interval, and 4. An untreated control. Averaging the 12 root nematode samplings, the lowest R. similis (P= 0.0008), Helicotylenchus spp. (P< 0.0001) and total nematode (P< 0.0001) population were observed in the plots treated with the three nematicide applications per year. Compared with the untreated control, the three nematicide applications reduced R. similis in 53%, Helicotylenchus spp. in 48% and the total nematode population in 53%. Even though the three nematicide applications per year resulted in higher R. similis control efficacy with 42.4%, no difference (P= 0.6372) was detected with two 32% (at 6-month interval) applications per year, and two 33% (at 7-month interval) applications per year, based on nematode population threshold. For Helicotylenchus spp. (P= 0.0047) and total nematodes (P= 0.0018), three applications were better than two at 6-month interval or two applications per year based on nematode population threshold, with 65.3 and 58.5% of efficacy on nematode control, respectively. No difference in total root weight (P= 0.9812) and functional root weight (P= 0.7742) was observed among treatments, varying from 88 to 90 and 73 to 79 g / plant, respectively. At harvest, 12 months after the nematicide applications, bunch weight was increased (P= 0.0013) in 7.2 (41%), 4.8 (27%) and 4.7 (27%) kg per bunch resulting in an extra gain of $2468, $1660 and $1427 ha -1 with three, two at 6- month interval and two applications per year based on nematode population density, respectively. Conclusions and application of findings: The non-fumigant nematicide applications reduced banana root nematodes and improved crop yield. Rotation of the nematicides according to their physic-chemical properties and weather conditions is desirable in order to prevent their biodegradation. Keywords: Chemical control, Musa AAA, nematode control, nematicides

Dehanding in Improving Fruit Quality of Banana

The experiment was conducted at the Horticultural Research Station, Mondouri, Bidhan Chandra Krishi Viswavidyalaya, West Bengal, India during the years 2007–2010 to assess the effect of dehanding on physico-chemical properties and quality of banana (Musa AAA Cv. Grande Naine). Accordingly terminal/distal hand(s) were removed in 3 (three) different intensity viz. i) removal of 1 (one) hand, ii) removal of 2 (two) hands and iii) removal of 3 (three) hands at various time after bunch emergence i.e, i) immediately after opening of last hand, ii) one week after opening of last hand, iii) two weeks after opening of last hand and iv) three weeks after opening of last hand. In general, dehanding decreased bunch weight over control and the intensity of reduction increased with delayed dehanding after opening of last hand. But removal of three hands immediately after opening of last hand increased fruit weight, fruit length, fruit circumference and pulp weight to the maximum tune of 53.9, 34.5, 13.9 and 58.6% respectively over the control. Unlike fruit morphological characters, the biochemical composition of fruits was not influenced significantly by dehanding except with reducing sugar. Dehanding also shortened the crop cycle by 18 days. The results signified the relevance of dehanding in improving market appeal and customer attraction of banana.

Effects of organic and inorganic fertilizers addition on growth and yield of banana (Musa AAA cv. Malindi) on a saline and non-saline soil in Oman

Water availability and soil salinity limit crop productivity in arid and semiarid regions such as Oman. The objective of this study was to examine the effects of amending a saline plant root zone soil with a non-saline sandy loam soil of organic and inorganic fertilizers, and of different placement methods on growth and yield of banana (Musa AAA cv. 'Malindi'). A total of 24 treatments comprising six fertilizer amendments, two soil types and two different application methods were tested. The amendments included four organic amendments versus un-composted dairy cow manure (FDM); composted dairy cow manure (CDM); CDM + 10% date palm straw (CDM + 10%DPS) by weight, and CDM + 30% date palm straw (CDM + 30% DPS) and two inorganic amendments (NPK and NPK plus foliar micronutrient spray, NPK+micro). The results revealed that neither soil amendments, fertilizer applications methods nor fertilizer composition significantly affected pseudostem height or girth, or leaf area. There was significant difference (P<0.05) in the number of leaves at flowering between Saline-Ring-NPK plants (8.2 leaves/plant) and Amended-Mixed-NPK and Amended-Ring-NPK+micro plants (14.0 and 13.8 leaves/plant, respectively). Amended-Ring-NPK+micro was significantly early flowering (267 days) compared to the other treatments. Amended-Ring-NPK+micro plants were harvested significantly earlier (in 339 days) than plants on saline soil. Amended-Ring-NPK+micro produced significantly higher average bunch fresh weight (9.5 kg/bunch/cycle) than all other treatments followed by Amended-Mixed-NPK+micro (5.9 kg/bunch/cycle). Key words: Dwarf cavendish, amendments, application methods, manure types, mineral fertilizers, yield components.

Histological changes and differences in activities of some antioxidant enzymes and hydrogen peroxide content during somatic embryogenesis of Musa AAA cv. Yueyoukang 1

To determine the possible involvement of oxidative stress in somatic embryogenesis of banana (Musa spp.), and provide a means to overcome the recalcitrance in embryogenesis, changes in histology, hydrogen peroxide (H2O2) content and antioxidant enzyme activities during banana somatic embryogenesis were investigated. From embryogenic cells (ECs) to early globular embryos, nearly all cells showed typical meristematic characteristics with a high nucleus/cytoplasm ratio. Cells started to lose their meristematic characteristic during later globular stage. Starch granules in cells showed spatial and temporal changes during somatic embryogenesis. POD (E.C.1.11.1.7) activity decreased significantly after transfer of ECs to the embryo regeneration medium which was followed by a significant increase and peaked at the late stages of embryogenesis. CAT (E.C.1.11.1.6) activity showed similar pattern, however its highest activity appeared in the ECs instead of the later embryos. On the contrary, a gradual increase in SOD (E.C.1.15.1.1) activity was observed after inoculation of ECs on embryo regeneration medium until the globular stage. Similarly to SOD activity, the hydrogen peroxide (H2O2) content also increased after inoculation of ECs on embryo regeneration medium and it peaked in proembryos, followed by a significant decrease in later embryogenic stages. The H2O2 content as well as activities of all tested antioxidant enzymes were significantly higher in ECs than in non-embryogenic cells. These results suggested that high levels of antioxidant enzyme activity and high H2O2 content were necessary for embryogenic competence of ECs while high H2O2 content played an important role in early development of somatic embryogenesis of banana.

Soil turnover of crop residues from the banana (Musa AAA cv. Petite-Naine) mother plant and simultaneous uptake by the daughter plant of released nitrogen

Banana (Musa sp.) residues contain two thirds of the plant nitrogen (N) content at harvest which may represent a large N source for the daughter plant and contribute to reducing fertilizer rates. Our aim was to assess the decomposition kinetics of above- and below-ground banana residues, and to determine the uptake of the released N by the daughter plant. Residue decomposition was analyzed under laboratory and field conditions, and plant N uptake was evaluated in the field using 15N-labelled above-ground residues. The decomposition kinetics was interpreted with a simulation model. In the laboratory, residue decomposition showed an immobilization phase followed by remineralization. The immobilization phase was longer and remineralization was smaller for roots due to their higher C:N ratio and lignin content. The model satisfactorily described both phases and the effect of the residue C:N ratio. Experimental and model results indicated that root residues would be a minor N source for the daughter plant. In the field, above-ground residues decomposed according to first order kinetics. Residue half-life was 2d in the laboratory and 32d in the field, which was due to poorer soil–residue contact in the field. At the time of harvest of the daughter plant, 39% of residue N was recovered in the plant, 54% in the topsoil, and 3% in the remaining residues. About 4% of residue N was probably lost by leaching. Nitrogen derived from residues represented 19% (14kgNha−1) of N in bunches of the daughter plant and 18% (39kgha−1) of the whole plant N. Our study showed that above-ground residue N was an effective N source for the daughter plant, with a good overlap between the period of N release and that of greatest plant demand which reduced the risk of N leaching.

Ultrastructural changes and the distribution of arabinogalactan proteins during somatic embryogenesis of banana (Musa spp. AAA cv. ‘Yueyoukang 1’)

A better understanding of somatic embryogenesis in banana (Musa spp.) may provide a practical way to improve regeneration of banana plants. In this study, we applied scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to visualize the ultrastructural changes during somatic embryogenesis of banana (Musa AAA cv. 'Yueyoukang 1'). We also used histological and immunohistochemical techniques with 16 monoclonal antibodies to study the spatial distribution and cellular/subcellular localization of different arabinogalactan protein (AGP) components of the cell wall during somatic embryogenesis. Histological study with periodic acid-Schiff staining documented diverse embryogenic stages from embryogenic cells (ECs) to the late embryos. SEM revealed a mesh-like structure on the surface of proembryos which represented an early structural marker of somatic embryogenesis. TEM showed that ECs were rich in juvenile mitochondria, endoplasmic reticulum and Golgi stacks. Cells in proembryos and early globular embryos resembled ECs, but they were more vacuolated, showed more regular nuclei and slightly more developed organelles. Immunocytochemical study revealed that the signal of most AGP epitopes was stronger in starch-rich cells when compared with typical ECs. The main AGP component in the extracellular matrix surface network of banana proembryos was the MAC204 epitope. Later, AGP immunolabelling patterns varied with the developmental stages of the embryos. These results about developmental regulation of AGP epitopes along with developmental changes in the ultrastructure of cells are providing new insights into the somatic embryogenesis of banana.

Terbufos biodegradability and efficacy against Radopholus similis in soils from banana cultivation having different histories of nematicide use, and the effect of terbufos on plant growth of in vitro-propagated Musa AAA cv. Grande Naine

The aims of this investigation were to: (1) determine whether there is enhanced biodegradability of terbufos in soils of banana plantations infested with Radopholus similis; (2) whether nematicide use history affects the degree of biodegradation; and (3) establish whether terbufos has phytotoxic side-effects on banana root growth. A greenhouse bioassay, using soils collected from different banana fields in Costa Rica, revealed that terbufos underwent enhanced biodegradation in the soil of a plantation having a long history of terbufos use. In the soils of two other plantations, where terbufos had never been used, and in another where the most recent terbufos application had occurred over a year before soil collection, high nematicide activity against R. similis was obtained even 60 days after application. Our study demonstrated that terbufos efficacy lasted longer in soils with no or low history of terbufos than in soils that had been treated several times. Terbufos did not reduce root fresh weight of in vitro-propagated bananas, and its positive effect was related to a control of R. similis.

The effect of plant growth regulators on somaclonal variation in Cavendish banana ( Musa AAA cv. ‘Z elig’)

The effect of the type and concentration of plant growth regulators and sub-culturing on somaclonal variation were studied in Cavendish banana cv. ‘ Zelig’ obtained from African Biotechnologies Ltd., South Africa. In vitro grown plants at the fourth multiplication cycle were used for the investigation. Auxins (IAA, IBA and NAA) and cytokinins (BA and TDZ) were used to multiply shoots for 10 generations. Bands generated through RAPD-PCR were scored according to whether they were present (1) or absent (0) to determine the extent of somaclonal variation. Results were then analyzed using cluster analysis. The relationship between multiplication rate and somaclonal variation was assessed using correlation analysis. Results indicated that treatments with higher multiplication rates produced more variants; sometimes as high as 72%. Dwarf off-types accounted for 88% of the variation. A dwarf-specific band, about 1500 kb in size, was amplified by the primer OPC-15. The band appeared consistently in normal plants but was absent in all dwarf plants.

Reproduction and pathogenicity of Helicotylenchus multicinctus, Meloidogyne incognita and Pratylenchus coffeae, and their interaction with Radopholus similis on Musa

Abstract The reproduction and pathogenicity of Helicotylenchus multicinctus, Meloidogyne incognita and Pratylenchus coffeae was studied on Musa AAA cv. Grande Naine pot plants and microplot plants. First, separate experiments using different inoculation numbers (between 218 and 4144) and different exposure times (between 8 and 22 weeks) were executed in pots for each nematode species. Helicotylenchus multicinctus suppressed root growth by 13%, comparing inoculated with uninoculated plants. In contrast, M. incognita stimulated root growth by 6.7%, while P. coffeae had no effect on root growth. The interaction between R. similis and each of these three nematode species was investigated in a concomitancy experiment in pots. Plants without concomitant species yielded the highest R. similis population densities but did not differ from plants previously inoculated with H. multicinctus and P. coffeae. Meloidogyne incognita was the only concomitant species that reduced R. similis population densities. Inoculation with R. similis affected the recovered numbers of P. coffeae albeit with large variability. In the microplot experiment, all four nematode species except H. multicinctus reduced the bunch weight of bananas, compared to uninoculated plants. Pratylenchus coffeae and R. similis increased root damage by 129 and 262%, respectively, while only the latter species suppressed root weight with 66%.

Histological analysis of direct organogenesis from micro-cross-sections of cultures of the banana

The histological origin of organogenesis was studied during plant regeneration of banana (Musa AAA cv. Williams) via direct organogenesis from micro-cross-sections of the rhizome in modified Murashige–Skoog (MS) medium (including 10 µm 6-BAP, 1 µm IAA and 50 µm KN). The frequency of the organogenesis was dependent on the position from where the explant was cut. Generally, more adventitious shoots were obtained from explants cut from regions close to apical meristem. The origin of adventitious shoots was multicellular, from cell layers with active cell division in the epidermis of the rhizome axis. After 24 h of culture, a layer of epidermal cells close to the leaf sheath base was actively dividing, and as the time in culture increased, regions containing actively dividing cells became enlarged. By the fifth day of culture, regions of actively dividing cells covered the whole peripheral zone of cortex. Several meristemoid structures were formed from the peripheral zone of cortex after 7 days of culture. These structures developed into adventitious shoots by the ninth day of culture. Vigorous plantlets could be regenerated from the shoots when they were transferred to rooting medium containing MS basal salts supplemented with 30 g L–1 sucrose, 6.5 g L–1 agar, a vitamin/amino acid mixture, 1 µm NAA and 1 µm 6-BAP.

Effect of weed management on nematode numbers and their damage in different root thickness and its relation to yield of banana ( Musa AAA cv. Grande Naine)

The effect of weed management on banana ( Musa AAA cv. Grande Naine) parasitic nematodes was evaluated under Costa Rican field conditions with special reference to their spatial distribution and the damage caused to roots of different thickness classes and their relation to yield losses. Root samples were taken at plant harvest, from soil blocks at 0–30,30–60 and 60–90 cm from the pseudostem, and at every 15 cm depth, from 0 to 120 cm. Weed management neither affected the nematode numbers nor their horizontal and vertical distribution and associated root damage. Differences in Radopholus similis ( P<0.0001), Helicotylenchus spp. ( P = 0.0115 ) and total nematode populations ( P<0.0001) were found in roots of different thickness. The average populations in thick, thin and fine roots were for R. similis 270,666 (57%), 120,401 (25%) and 11,313 (2%); for Helicotylenchus spp. 36,094 (7%), 22,508 (5%) and 8,824 (2%); and total nematodes 390,425 (65%), 145,534 (31%) and 21,177 (4%), respectively. No linear correlations were found between bunch weight and the number and density of nematodes or with their damage. Even though, no statistical difference was found in bunch weight, the manual weed control plot yielded 1.4 kg heavier bunches, which might have important implications for sustainable agriculture. The implementation of weed control by hand chopping may improve the physical, chemical and biological soil properties and reduce soil erosion, temperature fluctuations, evaporation rate, and nutrient leaching, and increase water infiltration. As a consequence of the decrease in herbicide applications, soil and air pollution might be reduced.