Endophytic Microorganisms for Improvement of Banana Vigour and Tolerance to Fusarium Wilt

This study explored the potential of endophytic microorganisms (EMS) isolated from wild bananas as biocontrol agents (BCAs) against Fusarium wilt caused by Fusarium oxysporum f. sp. cubense race 4 (FocR4) in susceptible banana ramets (Berangan cv. Intan). The fungal (Fusarium oxysporum (UPM31 PI)) and bacterial endophytes (Serratia marcescens (UPM39B3)) were established as effective BCAs; improving growth and vigour and enhancing tolerance of susceptible ramets to Fusarium wilt. They were antagonistic towards FocR4, with Percentage Inhibition of Radial Growth (PIRG) values of 65% and 63%, respectively. Inhibitory substances were produced in the form of volatile as well as non-volatile substances. The endophytes were also able to colonize the host tissues, including the roots and corms in artificial inoculation under laboratory conditions. The association of F. oxysporum (UPM31 PI) and S. marcescens (UPM39B3) with the host plants resulted in enhanced vegetative growth as shown by the increase in height, pseudostem diameter, root mass and total number of leaves ramet-'. Endophytes acted as elicitors in the production of inducible compounds associated with induced resistance (peroxidase, polyphenoloxidase, phenylalanine ammonia lyase, total soluble phenol and lignin content). The robust growth and occurrence of induced resistance subsequently enhanced tolerance of the ramets to Fusarium wilt based on parameters such as delay in onset of symptoms, lower percentages in disease incidence, disease severity, and epidemic rate. Inoculation with F. oxysporum singly was most effective followed by inoculation with mixture with S. marcescens (UPM31 Pl+UPM39B3). However, the survival and subsequent biocontrol efficacy of F. oxysporum (UPM31 PI) and S. marcescens (UPM39B3) might be vulnerable to the changing soil and environmental conditions. Populations of endophytes were not sustained over time. Therefore, further studies regarding formulation and application frequency and techniques, are essential to maximize the potential of F. oxysporum (UPM31P1) and S. marcescens (UPM39B3) as BCAs against Fusarium wilt of banana

Induction of Suppressive Soil in the Management of Fusarium Wilt on Banana Seedlings

This study detennined the potential of using artificially 'induced' suppressive soil to suppress the development of Fusarium wilt on susceptible banana seedlings (cultivar Berangan). Trichoderma harzianum (UPM 40) was selected as the microbial antagonist, and calcium nitrate (Ca(N03)2) as the soil amendment. Both biotic and abiotic components, respectively, were incorporated into the soil to mimic the contents of naturally existing Fusarium suppressive soils. The potential of T harzianum as a biocontrol agent was confirmed from the series of antagonism tests, with positive results in lysis, antibiosis and mycoparasitism tests. In vitro tests detennined that T harzianum required early establishment prior to challenge with Fusarium oxysporum f. sp. cubense race 4 (FocR4), to ensure effective antagonistic activity. Both T harzianum and FocR4 tolerated pH 5-8, and Ca2+ concentrations within 5-750 ppm. Soil pH was not affected by Ca(N03)2 application, indicating compatibility of inoculating T. harzzanum together with Ca(N03)2 application When tested on Berangan seedlings in the glasshouse, treatment with Ca(N03)2 alone provided better disease suppression compared to treatment with both T. harzzanum and Ca(N03h, and treatment with T. harzzanum alone. Treatment with Ca(N03)2 alone recorded low disease incidence (DI) of 5 1 % as compared to 59% and 69% from combined treatments and T. harzzanum alone, respectively, 8 weeks after inoculation. Calcium reduced the population of FocR4, promoted plant growth, and induced host resistance through increased peroxidase and polyphenoloxidase activity, and phenol content. Increased in enzymatic activities and phenol content was related to extensive cell wall lignification as revealed by histological observatlOns, resulting in resistance to FocR4 hyphal penetration. The formation of Ca-pectate also contributed to host resistance. Biocontrol efficiency of T. harzzanum was dependent on soil environment, as the glasshouse trial did not suppress disease incidence, contrary to its antagonistic effect in In vztro tests. T. harzzanum did not induce host resistarce, instead, predisposed the seedlings to infection by increasing root growth and infection sites. Disease suppression achieved through treatment with Ca(NE)3)2 was dependent on Ca2+ availability in the soil and Ca2+ content in the plant tissues. A more frequent application using suitable rates is then suggested as follow-up studies

Biological control of bacterial soft rot of cabbage

Bacterial soft rot disease, caused by Erwinia carotovora subsp. caratovora (Ecc), is one of the major postharvest diseases of cabbage throughout the world. Chemical control of this disease is ineffective and the high risk of residual content of chemicals in cabbbage might be hazardous to consumers. This study was therefore conducted to isolate and identify the potential antagonists that can inhibit the pathogen and hence reduce the disease severity. Two antagonistic bacteria, identified as Pseudomonas aeruginosa and Acinetobacter genospecies 15, were found to inhibit the growth of Ecc in vitro giving inhibition zones of 2.5cm and 1.0-1.5cm respectively. In vivo evaluation indicated that both antagonistic bacteria were able to reduce the disease severity up to 25%, upon treatment with 106-107 cfu ml of the antagonists

Influence of culture age on exopolymeric substances from common laboratory bacterial strains: a study on yield, profile and Cu(II) biosorption

Extracellular polymeric substances (EPS) produced by laboratory strains Bacillus cereus and Pseudomonas aeruginosa were extracted from cultures incubated at various incubation periods (24, 48, 72, 96 and 120 h). At each sampling time, the EPS were analysed for yield, quality, functional groups present, and their efficacies in copper (Cu(II)) biosorption (using 30 and 50 ppm EPS). Results revealed that EPS yield was influenced by incubation period, with 48-h culture of B. cereus and 96-h culture of P. aeruginosa producing the highest yield of EPS at 8.30 mg and 6.95 mg, respectively. The EPS produced at various incubation periods have similar characteristics in solubility, quality and major functional groups (C-O, CH3, C=C, O-H) present. Efficacy of Cu(II) biosorption was influenced by the amount of EPS used and the EPS-metal incubation time. Although Cu(II) removal was higher for EPS from 24-h B. cereus (18.96%) and 48-h P. aeruginosa (19.19%) when 30 ppm was used, application of 50 ppm EPS demonstrated no distinct differences in amount of Cu(II) removed. This suggested that higher biomass of EPS used and longer EPS-metal incubation period, superseded the efficacy of EPS from various incubation periods

Comparative effect of L-asparagine and sodium nitrate in inducing L-asparaginase production by endophytic Fusarium sp.

This study investigated the effect of two nitrogen sources (L-asparagine and sodium nitrate) on L-asparaginase production by endophytic Fusarium sp. (R19). L-asparagine is the more expensive nitrogen source, while sodium nitrate is the cheaper alternative of them. The production of L-asparaginase was quantified via Nesslerization and optimum incubation period was determined at 5-day intervals for 20 days. Fungal biomass obtained from supplementation of these nitrogen sources were weighed and correlated to the L-asparaginase production via Pearson correlation. Results revealed that sodium nitrate was unfortunately, inferior to L-asparagine in inducing L-asparaginase production in isolate R19. Supplementation with 1.25% L-asparagine yielded more L-asparaginase (3.01 U/mL), while the addition of sodium nitrate produced significantly lower levels (0.65 U/mL). The optimum incubation period was 5 and 10 days with supplementation of sodium nitrate and L-asparagine, respectively. Production of L-asparaginase correlates strongly to the fungal biomass (r = 0.990) suggesting nitrogen source impacts fungal growth and biomass, which subsequently influenced L-asparaginase production. To summarize, production of L-asparaginase from R19 was optimum with supplementation of 1.25% L-asparagine, incubated for 10 days. Sodium nitrate, although it is relatively cheap, was not effective in inducing L-asparaginase production. Further optimization studies can be performed to produce more L-asparaginase

In vitro endophyte-host plant interaction study to hypothetically describe endophyte survival and antifungal activities in planta

This study is the first to adopt a hypothetical approach to establish the influence of the complex endophyte-host interaction on endophyte survival and antifungal expression. Three k interactions were evaluated; (I) influence of host-induced enzymes on endophyte growth (biomass) and colonization, (II) link between endophyte-produced cellulase, their growth and colonization, and (III) the influence of host environment on antifungal expression of endophytes. The interactions with the host were performed using plant slurry (PS) to mimic in planta (host) environment with analysis on interactions evaluated using Pearson correlation coefficients (r). Results revealed that host induced enzymes may be a limiting factor to colonization of endophytes with inverse correlations observed (-0.046 ≤ r ≤-0.7164). These enzymes may also limit growth of endophyte although, PAL (r = 0.536) and TPC (r = 0.8894) appeared contrary. Results were also suggestive that endophytes produced cellulase to aid in colonization in host plants (r = 0.7073 in PS), and cellulase activities are continuously produced even when growth of endophytes are limited (r = -0.314 in PS). Endophytes are presumed to produce antifungal compounds in planta (r = 0.2760 in PS), and these compounds may be secondary metabolites, which are primarily produced under nutrient-depleted conditions where growth is poor (in host plant). The superior growth of endophytes in synthetic PDB media has an inverse correlation to antifungal activity (r = -0.5129), confirming that secondary metabolites are involved in antifungal activities. This study clearly presents that success of inoculated endophytes in colonizing, growing and expressing antifungal activities is dependent on the host plant

Endophytic microorganisms as potential growth promoters of banana.

The potential of endophytic microorganisms in promoting the growth of their host plant was determined by artificially introducing five isolates (bacterial and fungal strains: UPM31F4, UPM31P1, UPM14B1, UPM13B8, UPM39B3) isolated from the roots of wild bananas into both healthy and diseased banana plantlets (Berangan cv. Intan). The response of the host plants to endophytic infection was assessed by measuring the change in four growth parameters: plant height, pseudostem diameter, root mass and total number of leaves. The endophytes tested as growth promoters were found to have a significant effect in both healthy and Fusarium-infected (diseased) plantlets. In both experimental systems, the bacterial isolate UPM39B3 (Serratia) and fungal isolate UPM31P1 (Fusarium oxysporum) showed promising growth-promoting properties. Isolate UPM39B3 (Serratia) induced the largest increases in all four growth parameters in healthy plantlets – 3.14 cm (height), 1.12 cm (pseudostem diameter), 2.12 g (root mass) and 1.12 (total number of leaves plant−1) – followed by isolate UPM31P1 (Fusarium oxysporum). The beneficial effect of UPM39B3 (Serratia) and UPM31P1 (Fusarium oxysporum) was also reflected in the diseased plantlets, where pre-treatments with the isolates either singly (T6: UPM31P1; T8: UPM39B3) or in a mixture (T7: UPM31P1 + UPM39B3; T9: UPM14B1 + UPM13B8 + UPM39B3) were able to sustain the growth of plantlets, with significantly higher growth values than those in diseased plantlets that were not infected with endophytes (T10: FocR4). These results demonstrate the economic significance of these endophytic isolates, particularly UPM39B3 (Serratia) and UPM31P1 (Fusarium oxysporum), both as potential growth promoters of banana and as agents rendering tolerance towards Fusarium wilt as a strategy in the management of Fusarium wilt of banana via improved vegetative growth

Editorial : Endophytes and their biotechnological applications

[Abstract unavailable

Managing Fusarium wilt of bananas with endophytic microorganisms

Fusarium wilt of banana is a common disease in many banana growing countries worldwide. Attempts to control this disease using cultural practices, chemical application and breeding for resistant varieties, has met with little success. The pathogen, Fusarium oxysporum f. sp. cubense (Foc) spends part of its life cycle in the host tissues, thus ‘escaping’ the effect of control applications