A Genome-Wide Association Study on the Seedless Phenotype in Banana (Musa spp.) Reveals the Potential of a Selected Panel to Detect Candidate Genes in a Vegetatively Propagated Crop

Banana (Musa sp.) is a vegetatively propagated, low fertility, potentially hybrid and polyploid crop. These qualities make the breeding and targeted genetic improvement of this crop a difficult and long process. The Genome-Wide Association Study (GWAS) approach is becoming widely used in crop plants and has proven efficient to detecting candidate genes for traits of interest, especially in cereals. GWAS has not been applied yet to a vegetatively propagated crop. However, successful GWAS in banana would considerably help unravel the genomic basis of traits of interest and therefore speed up this crop improvement. We present here a dedicated panel of 105 accessions of banana, freely available upon request, and their corresponding GBS data. A set of 5,544 highly reliable markers revealed high levels of admixture in most accessions, except for a subset of 33 individuals from Papua. A GWAS on the seedless phenotype was then successfully applied to the panel. By applying the Mixed Linear Model corrected for both kinship and structure as implemented in TASSEL, we detected 13 candidate genomic regions in which we found a number of genes potentially linked with the seedless phenotype (i.e. parthenocarpy combined with female sterility). An additional GWAS performed on the unstructured Papuan subset composed of 33 accessions confirmed six of these regions as candidate. Out of both sets of analyses, one strong candidate gene for female sterility, a putative orthologous gene to Histidine Kinase CKI1, was identified. The results presented here confirmed the feasibility and potential of GWAS when applied to small sets of banana accessions, at least for traits underpinned by a few loci. As phenotyping in banana is extremely space and time-consuming, this latest finding is of particular importance in the context of banana improvement.

Anatomical and physical changes in leaves during the production of tamales

PREMISE OF THE STUDY

Tamale preparation has a long tradition in Mexico. To understand which material properties have been considered important for this purpose throughout the years, a study was conducted of the anatomical, chemical, and mechanical properties of the leaves of four plant species used in tamale preparation in Veracruz, Mexico: Calathea misantlensis, Canna indica, Musa paradisiaca, and Oreopanax capitatus.

METHODS

Four cooking treatments were considered: fresh (F), roasted (soasado, R), steamed (S), and roasted plus steamed (R/S). Chemical, anatomical, and mechanical analyses were conducted before and after each treatment. Leaf samples were tested for tensile strength at both parallel and perpendicular orientation relative to the fibers.

KEY RESULTS

Musa paradisiaca had the highest proportion of cellulose, while the remaining species shared similar lower proportions. Leaves were stronger and stiffer in the longitudinal direction of the fibers. Musa paradisiaca leaves had higher values of mechanical strength than the other species. The cooking process that most affected the mechanical properties was steaming.

CONCLUSIONS

The chemical constituents of the leaves are closely correlated with their physical properties. The treatment that caused the greatest decrease in leaf physical integrity was steaming, while the combination of roasting and steaming showed similar results to those of steaming alone. No evident anatomical changes are produced by any of the treatments. This is one of the few studies comparing physical, chemical, and anatomical characteristics of leaves used for human consumption, before and after cooking.

Salt stress aggravates boron toxicity symptoms in banana leaves by impairing guttation

Boron (B) is known to accumulate in the leaf margins of different plant species, arguably a passive consequence of enhanced transpiration at the ends of the vascular system. However, transpiration rate is not the only factor affecting ion distribution. We examine an alternative hypothesis, suggesting the participation of the leaf bundle sheath in controlling radial water and solute transport from the xylem to the mesophyll in analogy to the root endodermis. In banana, excess B that remains confined to the vascular system is effectively disposed of via dissolution in the guttation fluid; therefore, impairing guttation should aggravate B damage to the leaf margins. Banana plants were subjected to increasing B concentrations. Guttation rates were manipulated by imposing a moderate osmotic stress. Guttation fluid was collected and analysed continuously. The distribution of ions across the lamina was determined. Impairing guttation indeed led to increased B damage to the leaf margins. The kinetics of ion concentration in guttation samples revealed major differences between ion species, corresponding to their distribution in the lamina dry matter. We provide evidence that the distribution pattern of B and other ions across banana leaves depends on active filtration of the transpiration stream and on guttation.

Hypolipidaemic and antioxidant effects of fruits of Musa AAA (Chenkadali) in alloxan induced diabetic rats

Hypolipidaemic and antioxidant effects of ethanol extract of mature green fruits of Musa AAA (Chenkadali) was evaluated in alloxan induced diabetic rats. The effect of extract at two doses, 500 mg/kg body weight and 1000 mg/kg body weight was analysed and compared with a standard drug, glibenclamide. Rats administered with alloxan showed significantly increased levels of serum triacylglycerol, total cholesterol and alanine amino transferase (ALT) activity. Lipid peroxides increased significantly while reduced glutathione (GSH) decreased considerably in liver and pancreas. Oral administration of the ethanol extract of fruits of Musa AAA (Chenkadali) significantly decreased the levels of serum triacylglycerol, cholesterol and ALT activity. Significant decrease was also observed in the level of lipid peroxides while GSH content increased substantially in liver and pancreas. The effect was dose independent and rats treated with 500 mg/kg body weight showed comparable levels of serum triacylglycerol, cholesterol, ALT activity and liver lipid peroxides to that of normal control and glibenclamide treated groups. Although, there was no significant difference, treatment with 500 mg/kg body weight of the extract showed a higher content of GSH and lower level of lipid peroxides in pancreas compared with glibenclamide. Histopathological examination of pancreas and liver revealed regeneration of islet cells and hepatocytes respectively, which correlate with the biochemical findings. The present study shows that ethanol extract of mature green fruits of Musa AAA (Chenkadali) has antioxidant and hypolipidaemic properties and may be used for treating diabetes mellitus.

Functional anatomy controls ion distribution in banana leaves: significance of Na+ seclusion at the leaf margins

Typical salt stress symptoms appear in banana (Musa sp., cv. 'Grand Nain' AAA) only along the leaf margins. Mineral analysis of the dry matter of plants treated with increasing concentrations of KCl or NaCl revealed significant accumulation of Na+, but not of K+ or Cl(-), in the affected leaf margins. The differential distribution of the three ions suggests that water and ion movement out of the xylem is mostly symplastic and, in contrast to K+ and Cl(-), there exists considerable resistance to the flow of Na+ from the xylem to the adjacent mesophyll and epidermis. The parallel veins of the lamina are enclosed by several layers of bundle sheath parenchyma; in contrast, the large vascular bundle that encircles the entire lamina, and into which the parallel veins merge, lacks a complete bundle sheath. Xylem sap containing a high concentration of Na+ is 'pulled' by water tension from the marginal vein back into the adjacent mesophyll without having to cross a layer of parenchyma tissue. When the marginal vein was dissected from the lamina, the pattern of Na+ distribution in the margins changed markedly. The distinct anatomy of the marginal vein plays a major role in the accumulation of Na+ in the margins, with the latter serving as a 'dumping site' for toxic molecules.

Mobile sensor for high resolution NMR spectroscopy and imaging

In this work we describe the construction of a mobile NMR tomograph with a highly homogeneous magnetic field. Fast MRI techniques as well as NMR spectroscopy measurements were carried out. The magnet is based on a Halbach array built from identical permanent magnet blocks generating a magnetic field of 0.22T. To shim the field inhomogeneities inherent to magnet arrays constructed from these materials, a shim strategy based on the use of movable magnet blocks is employed. With this approach a reduction of the line-width from approximately 20kHz to less than 0.1kHz was achieved, that is by more than two orders of magnitude, in a volume of 21cm(3). Implementing a RARE sequence, 3D images of different objects placed in this volume were obtained in short experimental times. Moreover, by reducing the sample size to 1cm(3), sub ppm resolution is obtained in (1)H NMR spectra.

Biology of Pentalonia nigronervosa (Hemiptera, Aphididae) on banana using different rearing methods

The banana aphid, Pentalonia nigronervosa Coquerel, is present worldwide where banana (Musa spp.) is grown. It is the vector of Banana bunchy top virus (Nanoviridae, Babuvirus), the etiological agent of banana bunchy top disease, currently the most important constraint for banana producers in Hawaii. P. nigronervosa is not well studied, and effects of temperature on its growth and reproduction are unknown. We studied the longevity and fecundity of one clone of banana aphid on different types of plant materials to determine an effective method to study the insect in the laboratory. We found that insects performed better unconfined on plantlets, followed by leaf midrib cuttings. We also conducted complete life table studies with P. nigronervosa on banana leaf midrib cuttings at 20, 25, and 30 degrees C, with a photoperiod of 12:12. Intrinsic rate of increase (r), net reproductive rate (R0), doubling time (DT), nymphal mortality, and mean offspring per female all showed maximal rates at 25 degrees C. Population growth was studied on whole banana plantlets as well, and growth rates were also highest at 25 degrees C. We found r to be greater when aphids were reared on intact banana plantlets than on cuttings. Our results show the importance of comparing insect rearing methods for studies such as life tables.

Patterns of variability in the diameter of lateral roots in the banana root system

The relative importance of root system structure, plant carbon status and soil environment in the determination of lateral root diameter remains unclear, and was investigated in this study. Banana (Musa acuminata) plants were grown at various moderate levels of soil compaction in two distinct experiments, in a field experiment (FE) and in a glasshouse experiment (GE). Radiant flux density was 5 times lower in GE. The distribution of root diameter was measured for several root branching orders. Root diameters ranged between 0.09 and 0.52 mm for secondary roots and between 0.06 and 0.27 mm for tertiary roots. A relationship was found between the diameter of the parent bearing root and the median diameter of its laterals, which appears to be valid for a wide range of species. Mean lateral root diameter increased with distance to the base of the root and decreased with branching density [number of lateral roots per unit length of bearing root (cm(-1))]. Typical symptoms of low light availability were observed in GE. In this case, lateral root diameter variability was reduced. Although primary root growth was affected by soil compaction, no effects on lateral root diameter were observed.

Selection of assessment methods for evaluating banana weevil Cosmopolites sordidus (Coleoptera: Curculionidae) damage on highland cooking banana (Musa spp., genome group AAA-EA)

Cosmopolites sordidus (Germar) is an important pest on bananas and plantains. Population build-up is slow and damage becomes increasingly important in successive crop cycles (ratoons). Yield loss results from plant loss, mat disappearance and reduced bunch size. Damage assessment requires destructive sampling and is most often done on corms of recently harvested plants. A wide range of damage assessment methods exist and there are no agreed protocols. It is critical to know what types of damage best reflect C. sordidus pest status through their relationships with yield loss. Multiple damage assessment parameters (i.e. for the corm periphery, cortex and central cylinder) were employed in two yield loss trials and a cultivar-screening trial in Uganda. Damage to the central cylinder had a greater effect on plant size and yield loss than damage to the cortex or corm periphery. In some cases, a combined assessment of damage to the central cylinder and cortex showed a better relationship with yield loss than an assessment of the central cylinder alone. Correlation, logistic and linear regression analyses showed weak to modest correlations between damage to the corm periphery and damage to the central cylinder. Thus, damage to the corm periphery is not a strong predictor of the more important damage to the central cylinder. Therefore, C. sordidus damage assessment should target the central cylinder and cortex.