Potential of Bacillus spp as a biocontrol agent against Ralstonia bacterial wilt in bananas

Bacterial wilt disease in banana plants caused by Ralstonia solanacearum is an important disease that can reduce banana production. Until now there is no effective method to control this disease. The use of biocontrol agents such as Bacillus spp is an alternative method of controlling R. solanacearum in bananas. The aim of this study was to determine the activity of Bacillus spp against banana wilt disease caused by R. solanacearum. In vitro testing was carried out in the Plant Physiology Laboratory, Faculty of Agriculture, Pattimura University. The study used Bacillus subtilis strain SW116b and Bacillus subtilis strain HPC2-1 isolates. The results showed that the SW116b stain Bacillus subtilis has the highest activity against R. solanocearum, which is 10.5mm, so it has the potential as a biological control agent in suppressing the development of ralstonia wilt disease in bananas.

The relationship between the normalized difference vegetation index, rainfall, and potential evapotranspiration in a banana plantation of Venezuela

<p>The water supply for rainfed crops such as bananas in the Aragua state of Venezuela is often uncertain, particularly towards the beginning of the rainy season (April-May). Where climatic conditions are seasonal, the temporal evolution of the NDVI (Normalized Difference Vegetation Index) closely accompanies the interannual variation of vegetation growth in response to thermal and hydric factors. The aim of the study is to assess the relationship between NDVI, rainfall and potential evapotranspiration during the period of January/2016 to December/2017 in a Venezuelan banana plantation. In this study, the NDVI derived from the GIMMS MODIS Terra product, the daily accumulated precipitation data (mm) and the daily mean air temperature (°C) were used as the only way to estimate the potential evapotranspiration. The results showed that the GMOD09Q1-based NDVI reflects reasonably well the spatiotemporal variation in biomass accumulation. Besides, this provides information on the water stress conditions in banana plants at the plot level. The influence of Precipitation and potential evapotranspiration on the NDVI was more evident when a lag of 1 month was considered in terms of the Spearman r, implying that there is a delay in the banana phonological response to rainfall changes and dryness conditions. However, due to its low spatial resolution (i.e. 250 m), it is not adequate for the identification of banana wilt disease. Therefore, future studies are needed to assess other satellite-derived spectral indices for monitoring the health of banana plants over different sites in Venezuela.</p>

The exocyst regulates hydrolytic enzyme secretion at hyphal tips and septa in banana Fusarium wilt fungus, Fusarium odoratissimum

Hyphal polarized growth in filamentous fungi requires tip-directed secretion, while additional evidence suggests that fungal exocytosis for the hydrolytic enzyme secretion can occur at other sites in hyphae, including the septum. In this study, we analyzed the role of the exocyst complex involved in the secretion in banana wilt fungal pathogen Fusarium odoratissimum . All eight exocyst components in F. odoratissimum not only localized to the tips ahead of the Spitzenkörper in growing hyphae, but also localized to the outer edges of septa in mature hyphae. To further analyze the exocyst in F. odoratissimum , we tried to do single gene deletion for all the genes encoding the eight exocyst components and only succeed to construct the gene deletion mutants for exo70 and sec5 , we suspect that the other 6 exocyst components are encoded by essential genes. Deletion of exo70 or sec5 led to defects in vegetative growth, conidiation and pathogenicity in F. odoratissimum . Notably, the deletion of exo70 resulted in decreased activities for endoglucosidase, filter paper enzymes and amylase, while the loss of sec5 only led to a slight reduction in amylase activity. Septa-localized α-amylase (AmyB) was identified as the marker for septum-directed secretion, and we found that Exo70 is essential for the localization of AmyB to septa. Meanwhile the loss of Sec5 did not affect AmyB localization to septa but led to a higher accumulation of AmyB in cytoplasm. This suggested while Exo70 and Sec5 both take part in the septum-directed secretion, the two conduct different roles in this process. IMPORTANCE The exocyst complex is a multisubunit tethering complex (MTC) for secretory vesicles at the plasma membrane and contains eight subunits, Sec3, Sec5, Sec6, Sec8, Sec10, Sec15, Exo70 and Exo84. While the exocyst complex is well defined in eukaryotes from yeast to humans, the exocyst components in filamentous fungi show different localization patterns in the apical tips of hyphae that suggests filamentous fungi have evolved divergent strategies to regulate endomembrane trafficking. In this study, we demonstrated that the exocyst components in Fusarium odoratissimum are not only localized to the tips of growing hyphae but also to the outer edge of the septa in mature hyphae, suggesting that the exocyst complex plays a role in the regulation of septum-directed protein secretion in F. odoratissimum . We further found that Exo70 and Sec5 are required for the septum-directed secretion of α-amylase in F. odoratissimum but with different influence.

Isolation of Burkholderia sp. HQB-1, A Promising Biocontrol Bacteria to Protect Banana Against Fusarium Wilt Through Phenazine-1-Carboxylic Acid Secretion

Fusarium wilt is a devastating soil-borne fungal disease caused by Fusarium oxysporum f.sp. cubense (Foc). In recent years, some antifungal bacteria have been applied for the prevention and biocontrol of pathogenic fungi. In our study, a bacterial strain HQB-1, isolated from banana rhizosphere soil, was cultured for investigation. It showed broad-spectrum antifungal activities against representative phytopathogenic fungi including Fusarium oxysporum, Colletotrichum gloeosporioides, Botrytis cinerea, and Curvularia fallax. The strain HQB-1 was identified as Burkholderia sp. by morphological, physiological, and biochemical examinations, confirmed by 16S rRNA gene sequence analysis. Among the metabolites produced by the strain, we identified an antifungal compound which was identified phenazine-1-carboxylic acid (PCA) (C13H8N2O2) through ultraviolet, liquid chromatography quadrupole-time of flight mass spectrometer, and nuclear magnetic response. Furthermore, PCA exhibited the lowest minimum inhibitory concentration (MIC) against F. oxysporum (1.56 μg/ml) and yielded the highest MIC against C. gloeosporioides. Pot experiments showed that application of 5 μg/ml or more of PCA efficiently controlled banana wilt and promoted the growth of banana plants. These results suggested that Burkholderia sp. HQB-1, as an important microbial resource of PCA, could be a promising biological agent against wilt diseases and promoting banana growth.

First Morphological Detection of Non-Quarantine Pest Causing Banana Wilt in Morotai Island

<p>There are two symptoms of wilting in banana plants that have been widely known, namely fusarium wilt and bacterial wilt. The symptoms of banana wilt usually are attributed to pathogenic fungi. Wilting symptoms on the leaves are usually accompanied by leaf spot, leaf streak, leaf speckle and anthracnose. Recent quarantine pest<em> </em>reports have found the symptoms of banana wilt in Morotai Island, Indonesia. The pathogens attack many local cultivars of banana plants including Mas, Ambon, Kepok and Nangka. The study aimed to establish the morphological characters of the pathogens that cause banana wilt. Descriptive research began with the sampling of diseased symptomatic leaves, field data reports and identification of pathogenic morphological characters in the laboratory. The variable observed were the disease symptoms, color and shape of mycelia, conidia, kinds of the pathogens and their growth on agar medium. The results showed that there was no quarantine pest on the symptomatic banana samples. There were two non-quarantine pests that had been identified, i.e <em>Fusarium oxysporum</em> causing fusarium wilt and <em>Cladosporium musae</em> causing leaf speckle.</p>

The Novel Cerato-Platanin-Like Protein FocCP1 from Fusarium oxysporum Triggers an Immune Response in Plants

Panama disease, or Fusarium wilt, the most serious disease in banana cultivation, is caused by Fusarium oxysporum f. sp. cubense (FOC) and has led to great economic losses worldwide. One effective way to combat this disease is by enhancing host plant resistance. The cerato-platanin protein (CPP) family is a group of small secreted cysteine-rich proteins in filamentous fungi. CPPs as elicitors can trigger the immune system resulting in defense responses in plants. In this study, we characterized a novel cerato-platanin-like protein in the secretome of Fusarium oxysporum f. sp. cubense race 4 (FOC4), named FocCP1. In tobacco, the purified recombinant FocCP1 protein caused accumulation of reactive oxygen species (ROS), formation of necrotic reaction, deposition of callose, expression of defense-related genes, and accumulation of salicylic acid (SA) and jasmonic acid (JA) in tobacco. These results indicated that FocCP1 triggered a hypersensitive response (HR) and systemic acquired resistance (SAR) in tobacco. Furthermore, FocCP1 enhanced resistance tobacco mosaic virus (TMV) disease and Pseudomonas syringae pv. tabaci 6605 (Pst. 6605) infection in tobacco and improved banana seedling resistance to FOC4. All results provide the possibility of further research on immune mechanisms of plant and pathogen interactions, and lay a foundation for a new biological strategy of banana wilt control in the future.