Determining resistance to <Emphasis Type="Italic">Fusarium verticillioides</Emphasis> and fumonisin accumulation in African maize inbred lines resistant to <Emphasis Type="Italic">Aspergillus flavus</Emphasis> and aflatoxins

Fusarium verticillioides and Aspergillus flavus cause Fusarium ear rot (FER) and Aspergillus ear rot (AER) of maize, respectively. Both pathogens are of concern to producers as they reduce grain yield and affect quality. F. verticillioides and A. flavus also contaminate maize grain with the mycotoxins fumonisins and aflatoxins, respectively, which has been associated with mycotoxicosis in humans and animals. The occurrence of common resistance mechanisms to FER and AER has been reported. Hence, ten Kenyan inbred lines resistant to AER and aflatoxin accumulation were evaluated for resistance to FER, F. verticillioides colonisation and fumonisin accumulation; and compared to nine South African lines resistant to FER and fumonisin accumulation. Field trials were conducted at three localities in South Africa and two localities in Kenya. FER severity was determined by visual assessment, while F. verticillioides colonisation and fumonisin content were quantified by real-time PCR and liquid chromatography tandem mass spectrometry, respectively. Significant genotype x environment interactions was determined at each location (P ≤ 0.05). Kenyan inbred CML495 was most resistant to FER and F. verticillioides colonisation, and accumulated the lowest concentration of fumonisins across localities. It was, however, not significantly more resistant than Kenyan lines CML264 and CKL05015, and the South African line RO549 W, which also exhibited low FER severity (≤5%), fungal target DNA (≤0.025 ng μL^?1) and fumonisin levels (≤2.5 mg kg^?1). Inbred lines resistant to AER and aflatoxin accumulation appear to be promising sources of resistance to F. verticillioides and fumonisin contamination.     

Sources of resistance to Pseudocercospora fijiensis,the cause of black Sigatoka in banana

Black Sigatoka, caused by Pseudocercospora fijiensis, is one of the most devastating diseases of banana. In commercial banana-growing systems, black Sigatoka is primarily managed by fungicides. This mode of disease management is not feasible for resource-limited smallholder farmers. Therefore, bananas resistant to P. fijiensis provide a practical solution for managing the disease, especially under smallholder farming systems. Most banana and plantain hybrids with resistance to P. fijiensis were developed using few sources of resistance, which include Calcutta 4 and Pisang Lilin. To broaden the pool of resistance sources to P. fijiensis, 95 banana accessions were evaluated under field conditions in Sendusu, Uganda. Eleven accessions were resistant to P. fijiensis. Black Sigatoka symptoms did not progress past Stage 2 (narrow brown streaks) in the diploid accessions Pahang (AA), Pisang KRA (AA), Malaccensis 0074 (AA), Long Tavoy (AA), M.A. Truncata (AA), Tani (BB), and Balbisiana (BB), a response similar to the resistant control Calcutta 4. These accessions are potential sources of P. fijiensis resistance and banana breeding programmes can use them to broaden the genetic base for resistance to P. fijiensis.     

Inheritance of resistance to Fusarium oxysporum f. sp. cubense race 1 in bananas

Fusarium wilt of bananas (also known as Panama disease), caused by the soil-borne fungus Fusarium oxysporum f. sp cubense (Foc), is a serious problem to banana production worldwide. Genetic resistance offers the most promising means to the control of Fusarium wilt of bananas. In this study, the inheritance of resistance in Musa to Foc race 1 was investigated in three F₂ populations derived from a cross between ‘Sukali Ndizi’ and ‘TMB2X8075-7’. A total of 163 F₂ progenies were evaluated for their response to Fusarium wilt in a screen house experiment. One hundred and fifteen progenies were susceptible and 48 were resistant. Mendelian segregation analysis for susceptible versus resistant progenies fits the segregation ratio of 3:1 (χ² = 1.72, P = 0.81), suggesting that resistance to Fusarium wilt in Musa is conditioned by a single recessive gene. We propose panama disease 1 to be the name of the recessive gene conditioning resistance to Fusarium wilt in the diploid banana ‘TMB2X8075-7’.     

Stylar canal architecture of maize is not an indicator of resistance to Fusarium verticillioides infection

European Journal of Plant Pathology - Fusarium verticillioides causes Fusarium ear rot (FER) of maize and contaminates the grain with mycotoxins called fumonisins. Structural barriers that prevent...     

Disease development and mycotoxin production by the <Emphasis Type="Italic">Fusarium graminearum</Emphasis> species complex associated with South African maize and wheat

Fungal species comprising the Fusarium graminearum species complex (FGSC) may cause disease in maize and wheat. Host preference within the FGSC has been suggested, in particular F. boothii towards maize ears. Therefore, the disease development and mycotoxin production of five FGSC species in maize and wheat grain was determined. Eighteen isolates representing F. acaciae-mearnsii, F. boothii, F. cortaderiae, F. graminearum and F. meridionale were used. Each isolate was inoculated on maize ears and wheat heads to determine host preferences. Disease severity and disease incidence was measured for maize and wheat, respectively. Fungal colonisation and mycotoxins, deoxynivalenol (DON), nivalenol and zearalenone, was also quantified. Isolates differed significantly (P < 0.05) in their ability to produce symptoms on maize ears, however, no significant differences between FGSC species were determined. Similarly, significant differences (P < 0.05) between isolates but not between FGSC species in disease incidence on wheat were determined. The isolates also differed significantly (P < 0.05) in their ability to colonise maize and wheat grain. No significant differences in fungal colonisation, among the five FGSC species, were determined in field grown maize. However, under greenhouse conditions, F. boothii was the most successful coloniser of maize grain (P < 0.05). In wheat, F. graminearum colonised the grain more successfully and produced significantly more (P < 0.05) DON than the other species. Fusarium boothii isolates were the best colonisers and mycotoxin producers in maize, and F. graminearum isolates in wheat. The selective advantage of F. boothii to cause disease on maize was supported in this study.     

Back to the roots: Understanding banana below-ground interactions is crucial for effective management of Fusarium wilt

Global banana production is affected by Fusarium wilt, a devastating disease caused by the soilborne root-infecting fungus, Fusarium oxysporum f. sp. cubense (Foc). Fusarium wilt is notoriously difficult to manage because infection arises through complex below-ground interactions between Foc, the plant, and the soil microbiome in the root–soil interface, defined as the rhizosphere. Interactions in the rhizosphere play a pivotal role in processes associated with pathogen development and plant health. Modulation of these processes through manipulation and management of the banana rhizosphere provides an auspicious prospect for management of Fusarium wilt. Yet, a fundamental understanding of interactions in the banana rhizosphere is still lacking. The objective of this review is to discuss the state-of-the-art of the relatively scant data available on banana below-ground interactions in relation to Fusarium wilt and, as a result, to highlight key research gaps. Specifically, we seek to understand (a) the biology of Foc and its interaction with banana; (b) the ecology of Foc, including the role of root-exuded metabolites in rhizosphere interactions; and (c) soil management practices and how they modulate Fusarium wilt. A better understanding of molecular and ecological factors influencing banana below-ground interactions has implications for the development of targeted interventions in the management of Fusarium wilt through manipulation of the banana rhizosphere.     

Molecular identification of two vegetative compatibility groups of Fusarium oxysporum f. sp. cepae

Fusarium oxysporum f. sp. cepae, which causes basal rot of onion, consists of seven vegetative compatibility groups (VCGs 0420 to 0426) and several single-member VCGs (SMVs). F. oxysporum f. sp. cepae populations in South Africa and Colorado each consist of one main VCG (namely, VCG 0425 and 0421, respectively). The aim of this study was to develop sequence-characterized amplified region (SCAR) markers for the identification of VCGs 0425 and 0421, using 79 previously characterized F. oxysporum isolates. A second aim was to investigate the prevalence of VCG 0425 among 88 uncharacterized South African onion F. oxysporum isolates using (i) the developed SCAR markers and (ii) inter-retrotransposon (IR)- and random amplified polymorphic DNA (RAPD) fingerprinting. Only two RAPD primers provided informative fingerprints for VCG 0425 isolates but these could not be developed into SCAR markers, although they provided diagnostic fragments for differentiation of VCG 0425 from VCG 0421. IR fingerprinting data were used to develop a multiplex IR-SCAR polymerase chain reaction method for the identification of VCG 0421, VCG 0425, and SMV 4 isolates as a group. Molecular identification of the uncharacterized collection of 88 F. oxysporum isolates (65 F. oxysporum f. sp. cepae and 23 F. oxysporum isolates nonpathogenic to onion) confirmed that VCG 0425 is the main VCG in South Africa, with all but 3 of the 65 F. oxysporum f. sp. cepae isolates having the molecular characteristics of this VCG. Genotyping and VCG testing showed that two of the three aforementioned isolates were new SMVs (SMV 6 and SMV 7), whereas the third (previously known as SMV 3) now belongs to VGC 0247.