Spent Substrate of Pleurotus ostreatus Has Potential for Managing Fusarium Wilt of Banana

A range of basidiomycetes including the edible mushroom Pleurotus ostreatus (Po) can suppress plant pathogens such as Fusarium spp. With the current increase in production and consumption of Po in Uganda, the spent Po substrate (SPoS) could be an alternative to manage Fusarium wilt of banana (FWB), caused by the soil borne pathogen Fusarium oxysporum f. sp. cubense, race 1 (Foc). This study determined the potential of SPoS to inhibit Foc in vitro and in potted plants. In vitro studies confirmed suppression of Foc in pure co-culture (Po vs. Foc) assays and media amended with different concentrations (0% to 50% w/v) of un-sterilized SPoS filtrates. Foc growth in the sterile SPoS filtrate was comparable to the water control, suggesting possible roles of biotic or thermolabile components of the SPoS. To further verify the suppressive effects of SPoS, pot experiments were carried out with a resistant (‘Mbwazirume’, AAA) and susceptible (‘Sukali Ndizi’, AAB) banana cultivar using both artificially and naturally infested soils. Independent of the inoculation method, SPoS significantly reduced the severity of FWB in pot experiments. Susceptible cultivar ‘Sukali Ndizi’ growing in substrates amended with SPoS showed lower (1.25) corm damage (Scale 0–5) than the un-amended control (3.75). No corm damage was observed in uninoculated controls. The resistant cultivar ‘Mbwazirume’, showed slight (0.25) corm damage only in the Foc-inoculated plants without SPoS. These findings suggest that SPoS could be used as part of the management practices to reduce the impact of FWB.

Biological Control of Fusarium oxysporum f. sp. cubense Tropical Race 4 Using Natively Isolated Bacillus spp. YN0904 and YN1419

Fusarium wilt of banana (FWB) is the main threatening factor for banana production worldwide. To explore bacterial biocontrol resources for FWB, the antagonistic effective strains were isolated from banana-producing areas in Yunnan Province, China. Two isolates (YN0904 and YN1419) displaying strong antagonism against Tropical Race 4 (TR4) were identified from a total of 813 strains of endophytic bacteria. TR4 inhibition rates of YN0904 and YN1419 were 79.6% and 81.3%, respectively. By looking at morphological, molecular, physiological and biochemical characteristics, YN0904 was identified as Bacillus amyloliquefaciens, while YN1419 was identified as as B. subtillis. The control effects of YN0904 and YN1419 on TR4 in greenhouse experiments were 82.6% and 85.6%, respectively. Furthermore, YN0904 obviously promoted the growth of banana plantlets. In addition, biocontrol marker genes related to the biosynthesis of antibiotics synthesized and auxin key synthetase genes could be detected in YN0904. Surprisingly, the marker gene sboA could be exclusively detected in YN1419, while other marker genes were all absent. Molecular characterization results could provide a theoretical basis for expounding the biocontrol mechanisms of these two strains. We concluded that natively antagonistic strains derived from local banana plantations could provide new biological control resources for FWB.

Fusarium Wilt of Banana in Kisii County, Kenya.

Banana categorized as third in world’s key starch crops after cassava and sweet potatoes and it is the fourth most widely grown crop after rice, wheat and maize. The crop accounts for over 70 % of farmer’s earnings in Kisii county of Kenya. Farmers growing the crop are facing several challenges including depletion of soil fertility, low yields and diseases especially Fusarium wilt caused by Fusarium oxysporum f.sp. cubense (Foc). A study was conducted to determine the status of this disease in Kisii County. Ten farms were sampled in each Agro-ecological zone and in each farm four symptomatic and four non-symptomatic mats were sampled. Incidence was determined by relating banana seedlings affected and the total number of banana seedlings planted while severity was determined by measuring the extent of the damage/brown discoloration of the stem in length. Banana roots and pseudostem cuttings that were infected with the disease were used for isolation of the pathogen.Fusarium wilt is common in banana producing regions of Kisii County, however, the management practices are poor and do not meet the required strategies for controlling the disease. It was established that only; wood-ash and poultry manure were used by a few farmers in managing this disease. Present report is an attempt to improve the understanding of distribution and diversity of Foc in banana producing regions of Kisii County thereby aiding formulation of appropriate mitigation measures which the farmers can adopt locally.

The M35 Metalloprotease Effector FocM35_1 Is Required for Full Virulence of Fusarium oxysporum f. sp. cubense Tropical Race 4

Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) causes Fusarium wilt of banana, the most devastating disease on a banana plant. The genome of Foc TR4 encodes many candidate effector proteins. However, little is known about the functions of these effector proteins on their contributions to disease development and Foc TR4 virulence. Here, we discovered a secreted metalloprotease, FocM35_1, which is an essential virulence effector of Foc TR4. FocM35_1 was highly upregulated during the early stages of Foc TR4 infection progress in bananas. The FocM35_1 knockout mutant compromised the virulence of Foc TR4. FocM35_1 could interact with the banana chitinase MaChiA, and it decreased banana chitinase activity. FocM35_1 induced cell death in Nicotiana benthamiana while suppressing the INF1-induced hypersensitive response (HR), and its predicted enzymatic site was required for lesion formation and the suppression to INF1-induced HR on N. benthamiana leaves. Importantly, treatment of banana leaves with recombinant FocM35_1 accelerates Foc TR4 infection. Collectively, our study provides evidence that metalloprotease effector FocM35 seems to contribute to pathogen virulence by inhibiting the host immunity.

A Real-Time Fluorescent Reverse Transcription Quantitative PCR Assay for Rapid Detection of Genetic Markers’ Expression Associated with Fusarium Wilt of Banana Biocontrol Activities in Bacillus

Fusarium wilt of banana, caused by Fusarium oxysporum f. sp. cubense (Foc), especially Tropical Race 4 (TR4), seriously threatens banana production worldwide. There is no single effective control measure, although certain Bacillus strains secrete antibiotics as promising disease-biocontrol agents. This study identified five Bacillus strains displaying strong antibiotic activity against TR4, using a systemic assessment for presence/absence of genetic markers at genome level, and expression profiles at transcriptome level. A conventional PCR with 13 specific primer pairs detected biocontrol-related genes. An accurate, quantitative real-time PCR protocol with novel designed specific primers was developed to characterise strain-specific gene expression, that optimises strain-culturing and RNA-isolation methodologies. Six genes responsible for synthesising non-ribosomal peptide synthetase biocontrol metabolites were detected in all five strains. Three genes were involved in synthesising three Polyketide synthetase metabolites in all five strains, but the macrolactin synthase gene mln was only detected in WBN06 and YN1282-2. All five Bacillus strains have the genes dhb and bioA, essential for synthesising bacillibactin and biotin. However, the gene sboA, involved in subtilisin synthesis, is absent in all five strains. These genes’ expression patterns were significantly different among these strains, suggesting different mechanisms involved in TR4 biocontrol. Results will help elucidate functional genes’ biocontrol mechanisms.

Improvements in the Resistance of the Banana Species to Fusarium Wilt: A Systematic Review of Methods and Perspectives

The fungus Fusarium oxysporum f. sp. cubense (FOC), tropical race 4 (TR4), causes Fusarium wilt of banana, a pandemic that has threatened the cultivation and export trade of this fruit. This article presents the first systematic review of studies conducted in the last 10 years on the resistance of Musa spp. to Fusarium wilt. We evaluated articles deposited in different academic databases, using a standardized search string and predefined inclusion and exclusion criteria. We note that the information on the sequencing of the Musa sp. genome is certainly a source for obtaining resistant cultivars, mainly by evaluating the banana transcriptome data after infection with FOC. We also showed that there are sources of resistance to FOC race 1 (R1) and FOC TR4 in banana germplasms and that these data are the basis for obtaining resistant cultivars, although the published data are still scarce. In contrast, the transgenics approach has been adopted frequently. We propose harmonizing methods and protocols to facilitate the comparison of information obtained in different research centers and efforts based on global cooperation to cope with the disease. Thus, we offer here a contribution that may facilitate and direct research towards the production of banana resistant to FOC.

The Banana Root Endophytome: Differences between Mother Plants and Suckers and Evaluation of Selected Bacteria to Control Fusarium oxysporum f.sp. cubense

This study aimed to disentangle the structure, composition, and co-occurrence relationships of the banana (cv. Dwarf Cavendish) root endophytome comparing two phenological plant stages: mother plants and suckers. Moreover, a collection of culturable root endophytes (>1000) was also generated from Canary Islands. In vitro antagonism assays against Fusarium oxysporum f.sp. cubense (Foc) races STR4 and TR4 enabled the identification and characterization of potential biocontrol agents (BCA). Eventually, three of them were selected and evaluated against Fusarium wilt of banana (FWB) together with the well-known BCA Pseudomonas simiae PICF7 under controlled conditions. Culturable and non-culturable (high-throughput sequencing) approaches provided concordant information and showed low microbial diversity within the banana root endosphere. Pseudomonas appeared as the dominant genus and seemed to play an important role in the banana root endophytic microbiome according to co-occurrence networks. Fungal communities were dominated by the genera Ophioceras, Cyphellophora, Plecosphaerella, and Fusarium. Overall, significant differences were found between mother plants and suckers, suggesting that the phenological stage determines the recruitment and organization of the endophytic microbiome. While selected native banana endophytes showed clear antagonism against Foc strains, their biocontrol performance against FWB did not improve the outcome observed for a non-indigenous reference BCA (strain PICF7).