Biochemical markers as a useful tool for the early identification of Fusarium oxysporum f.sp. cubense,race 1 resistance banana clones

Abstract

Panama disease of banana (Musa spp) caused by the fungus Fusarium oxysporum f. sp. Cubense (FOC), is a serious constraint both to the commercial production of banana and cultivation for subsistence agriculture. Chemical control is not economically effective and is also hazardous to the environment and human health. Breeding for disease resistance is an alternative strategy, which leads to the development of resistance clones. Field evaluation is the most reliable method of screening for disease resistance, but it is demanding in terms of cost, manpower and space requirements. Another approach of screening hybrids at the sucker's stage (planting material) through biochemical markers has been found to be effective in early identification of resistant hybrids. The resistance mechanisms involving the role of phenol, PAL, oxidative enzymes like peroxidase (PO), polyphenol oxidase (PPO), superoxide dismutase (SOD), catalase and PR-proteins like chitinase, β-1-3 glucanase were studied and they showed relatively higher activity in resistant hybrids than susceptible hybrids. Isozyme analysis of peroxidase (PO) and polyphenol oxidase (PPO) was also carried out in cultivars and hybrids, which revealed the induction of specific isoforms in the resistant hybrids upon challenge inoculation. This could be a useful tool for early identification of F. oxysporum f. sp. cubense resistance banana clones.     

Synthesis of 2-(4-Hydroxyphenyl)naphthalene-1,8-dicarboxylic Anhydride,a Phytoalexin Isolated from Unripe Banana (Musa acuminata)

2-(4-Hydroxyphenyl)naphthalene-1,8-dicarboxylic anhydride, a component of the phytoalexin that has been isolated from the peel of unripe banana (Musa acuminata), was synthesized from 3-bromoacenaphthene.     

Low Inbreeding and High Pollen Dispersal Distances in Populations of Two Amazonian Forest Tree Species

Recent studies suggest that tropical tree species exhibit low inbreeding and high gene dispersal levels despite the typically low density of conspecifics in tropical forests. To examine this, we undertook a study of pollen gene dispersal and mating system of two Amazonian tree species. We analyzed 341 seeds from 33 trees at four microsatellite loci in a Carapa guianensis population from Brazil, and 212 seeds from 22 trees at four microsatellite loci in a Sextonia rubra population from French Guiana. Differentiation of allele frequencies among the pollen pool of individual trees was Φ_FT= 0.053 (95% CI: 0.027–0.074) for C. guianensis and Φ_FT= 0.064 (95% CI: 0.017–0.088) for S. rubra. The mean pollen dispersal distances were estimated at 69–355 m for C. guianensis , and 86–303 m for S. rubra , depending on the pollen dispersal model and the estimate of reproductive tree density used. The multi-locus outcrossing rate was estimated at 0.918 and 0.945, and the correlation of paternity at 0.089 and 0.096, for C. guianensis and S. rubra , respectively, while no significant levels of biparental inbreeding were detected. Comparing trees with high and low local density of conspecifics, we found no evidence for differences in inbreeding levels. The results are discussed within the framework of the emerging picture of the reproductive biology of tropical forest trees.     

Exopolysaccharides produced by mixed culture of yeast Rhodotorula rubra GED10 and yogurt bacteria (Streptococcus thermophilus 13a + Lactobacillus bulgaricus 2-11)

AIMs: The studies of the production of exopolysaccharides by lactose-negative yeast and a yogurt starter co-cultivated in a natural substrate containing lactose may be considered of interest because they reveal the possibilities for high-efficiency synthesis of biopolymers by mixed cultivation. METHODS AND RESULTS: The mixed culture Rhodotorula rubra GED10 + (Streptococcus thermophilus 13a + Lactobacillus bulgaricus 2-11) was cultivated in cheese whey ultrafiltrate (WU) (44.0 g lactose l(-1)) at initial pH 6.0, 28 degrees C, under intensive aeration (air-flow rate 1.0 l l(-1) min(-1), agitation 220 rev min(-1)) in a MBR AG fermentor. The mixed culture manifested the highest activity for synthesis of exopolysaccharides (19.3 g l(-1)) and cell mass (21.0 g l(-1)) at the 84th hour. The yogurt starter synthesized neutral exopolysaccharides, while the mixed culture yeast + yogurt starter produced acidic exopolysaccharides containing uronic acid (6%). The neutral sugar composition was identified as mannose, glucose, galactose, xylose and arabinose. Mannose dominated in the polymer composition (83%) that was produced only by the yeast (97%). CONCLUSIONS: Lactose in the WU can be effectively utilized by a co-culture of lactose-negative yeast-yogurt starter for synthesis of exopolysaccharides. SIGNIFICANCE AND IMPACT OF THE STUDY: The present findings propose an alternative use of WU as a cost-effective carbohydrate substrate, and suggest that the lactose-negative yeast Rhodotorula rubra can have industrial application as producers of exopolysaccharides.     

Lactones. 6. Microbial lactonization of gamma,delta-epoxy esters

The ability of 19 microorganisms to perform the enantioselective lactonization of racemic gamma,delta-epoxy ester 3a and its 7-methyl homolog 3b was checked. It was found that Rhodotorula rubra preferentialy transformed both substrates to (-)-enantiomers of trans delta-hydroxy-gamma-lactones with ee 76% for 3a and 24% for 3b. The best efficiency (20-30%) and enantioselectivity (ee 60-100%) of formation of (-)-gamma-hydroxy-delta-lactones 6a and 6b was observed for lactonization by Botrytis cinerea and Fusarium semitectum, respectively.     

Number,position, diameter and initial direction of growth of primary roots in Musa

To understand soil colonization by a root system, information is needed on the architecture of the root system. In monocotyledons, soil exploration is mainly due to the growth of adventitious primary roots. Primary root emergence in banana was quantified in relation to shoot and corm development. Root emergence kinetics were closely related to the development of aerial organs. Root position at emergence on the corm followed an asymptotic function of corm dry weight, so that the age of each root at a given time could be deduced from its position. Root diameter at emergence was related to the position of the roots on the corm, with younger roots being thicker than older ones. However, root diameters were not constant along a given root, but instead decreased with the distance to the base; roots appear to be conical in their basal and apical parts. Root growth directions at emergence were variable, but a high proportion of the primary roots emerged with a low angle to the horizontal. Further research is needed to evaluate whether these initial trajectories are conserved during root development. Results presented in this study are in good agreement with those reported for other monocotyledons such as maize and rice. They give quantitative information that will facilitate the development of models of root system architecture in banana.     

Physical mapping of the 18S-25S and 5S ribosomal RNA genes in diploid bananas

Fluorescent in situ hybridisation (FISH) was used to determine the number and distribution of the 18S-25S and 5S rDNA sites on mitotic chromosomes of 6 wild and 2 edible diploid (2n=22) accessions belonging to the two banana species, Musa acuminata and M. balbisiana. FISH with the 18S-25S probe resulted in signals on one pair of chromosomes, the position of signals corresponded to the secondary constriction at the end of a short arm. The intensity of labelling was different between the homologues and the larger site corresponded to a larger secondary constriction. This labelling pattern was observed consistently in all genotypes. On the other hand, differences in the number of 5S sites were observed between the accessions. While in some of the wild seeded species, the 5S rDNA was localised on two pairs of chromosomes, hybridisation signals appeared on three pairs of chromosomes in other wild accessions. Quite unexpectedly, only five sites of 5S rDNA were reproducibly observed in the two vegetatively propagated diploid edible cultivars, Pisang Mas and Niyarma Yik, evidence for structural heterozygosity. A dual colour FISH showed that in all accessions, the satellite chromosomes carrying the 18S-25S loci did not carry the 5S loci. The results demonstrate that molecular cytogenetics can be applied to Musa and that physical cytogenetic maps can be generated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Growth of arbuscular mycorrhizal mycelium in calcareous dune sand and its interaction with other soil microorganisms as estimated by measurement of specific fatty acids

Fatty acid analysis was used for determining the extent of the development of the external mycelium of AM fungi (mixed inoculum from a sand dune) growing from roots of Festuca rubra and Plantago lanceolata in calcareous dune sand. The plants were raised in chambers specially designed to permit the growth of AM mycelium in root-free compartments. In two separate experiments, growth of external mycelium in the root-free compartments was detected and the amount of mycelium was estimated using the indicator of AM fungal biomass, phospholipid fatty acid (PLFA) 16:15. The results showed that the PLFA 16:15 was suitable for estimating the mycelium emerging from the mixed inoculum obtained from the field roots of F. rubra and P. lanceolata.The PLFA 16:15 showed external mycelium to become established in the root-free compartments within a period of 3 weeks and the amount of mycelium to continue to increase at 6 and 9 weeks. Increases in neutral lipid fatty acid (NLFA) 16:15 (indicator of storage lipids) over time were inconsistent between the two experiments, but appeared to follow patterns of sporulation in each experiment.In both experiments, the root-free compartment was colonised by saprophytic fungi to a greater extent in the case of non-mycorrhizal than of AM treatment, as indicated by an increase in PLFA 18:26,9 (indicator of saprophytic fungi). The absence of an increase in the case of AM treatment indicates that AM fungal mycelium can negatively affect the growth of saprophytic fungi in this soil type. This result was, however, only weakly supported by measurements of ergosterol content. The analysis of bacteria specific PLFAs showed that bacterial biomass was not affected by the AM mycelium.     

Antibacterial Δ1‐3‐Ketosteroids from the South China Sea Gorgonian Coral Subergorgia rubra

Three new Δ¹‐3‐ketosteroids characterized with a 9‐OH, subergosterones A–C ( 1 – 3 ), together with five known analogs 4 – 8 , were obtained from the gorgonian coral Subergorgia rubra collected from the South China Sea. The structures of 1 – 3 , including their absolute configurations, were determined by comprehensive spectroscopic methods and electronic circular dichroism (ECD) experiments. Compounds 2 and 3 exhibited inhibitory antibacterial activities against Bacillus cereus with MIC values of 1.56 μM .     

Plantlet production from the male inflorescence tips of <Emphasis Type="Italic">Musa acuminata</Emphasis> cultivars from South India

Inflorescence apices are suitable explants for the rapid in vitro propagation of Musa spp. However, the diploid and triploid banana cultivars showed different in vitro responses with respect to the hormone combinations in Murashige and Skoog medium. The diploid cultivar (Sannachenkadali, AA) induced a maximum number of multiple shoots in 8.9 μM 6-benzyl adenine (BA) whereas the triploid cultivar (Red banana, AAA) exhibited maximum multiplication in 22.2 μM 6-benzyl adenine. MS medium supplemented with 11.4 μM indole acetic acid and 17.8 μM BA was also suitable for shoot proliferation in triploid cultivar but not in the diploid cultivar. The regenerated shoots were rooted in Murashige and Skoog basal medium within 10–15 days. The rooted plantlets were transferred to vermiculite and maintained at a temperature of 25 ± 2°C for 10 days and then at room temperature (30–32°C) for 2 weeks before transferring to potted soil compost mixture. The plantlets showed 100% survival.