Fusarium basal rot (FBR) is a soil-borne disease that affects Allium species worldwide. Although FBR has long been recognized as a major constraint to the production of economically important Allium species, information that could support disease management remains scattered. In this review, the current knowledge on the causal agents, symptomology and epidemiology, impact, and management strategies of FBR is synthesized. We highlight that FPR is associated with different complexes of several Fusarium species, of which Fusarium oxysporum and F. proliferatum are the most prevalent. These pathogenic complexes vary in composition and virulence, depending on sites and hosts, which can be challenging for disease management. Research to improve disease management using chemical pesticides, resistance cultivars, biocontrol agents, and cultural practices has achieved both promising results and limitations. Finally, research needs and future directions are proposed for the development of effective FBR management strategies.

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Fusarium basal rot: profile of an increasingly important disease in Allium spp.

Potato is a globally important crop whose production is severely damaged by black scurf disease (stem cankers and tuber blemishes) caused by soil-borne fungus, Rhizoctonia solani. This study was undertaken to assess antifungal potential of Carthamus oxycantha extracts and detection of likely antifungal components by GC-MS. In laboratory bioassays, antifungal activity of methanolic extracts of leaf, stem, root and inflorescence of C. oxycantha was checked using a range of concentrations from 1.562 to 200 mg mL. The leaf extract significantly suppressed fungal growth. Methanolic leaf extract was subjected to GC-MS analysis. A total of 95 compounds were found present in this extract. Predominant compound was D-ribofuranose, 5-deoxy-5-(methylsulfinyl)-1,2,3-tris-O-(trimethylsilyl)(13.312%) followed by benzoic acid, 4-hydroxy-3methoxy-, methyl ester (11.888%), bis(2-ethylhexyl) phthalate (9.842%), 4-hydroxy-2,2',4',6'-tetrachlorobiphenyl, trimethylsilyl ether (6.837%) and pentanedioic acid (4.926%). Besides, a number of free fatty acids and fatty acid methyl esters with known antifungal potential were also identified as minor compounds.

Antifungal activity of methanolic leaf extract of Carthamus oxycantha against Rhizoctonia solani

Sclerotium rolfsii is a soil-borne plant pathogen that causes root diseases in hundreds of plant species. It also causes collar rot disease in chickpea (Cicer arietinum L.). The present pot study was carried out to investigate the effect of soil amendment with dry biomass of a weed Chenopodium album L. and two antagonistic fungi, namely Trichoderma harzianum and T. viride, on growth and yield of chickpea variety Noor 2009 in soil infected with S. rolfsii. The pathogen-contaminated soil was amended either with 1, 2, or 3% C. album dry biomass, T. harzianum, and T. viride alone, or combinations of either of the two Trichoderma species and plant dry biomass. The lowest shoot and root dry biomass and grain yield of chickpea were recorded in S. rolfsii inoculation alone without any soil amendment (positive control). Plant growth and yield were significantly and gradually increased over positive control with an increase in C. album dry biomass application in the soil. Likewise, soil application of either of the two Trichoderma species significantly enhanced plant growth and yield over positive control under biotic stress of S. rolfsii. Combined application of either T. harzianum or T. viride with 3% dry biomass of C. album also proved highly effective in alleviating biotic stress of S. rolfsii on growth and yield of chickpea.

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Effect of soil amendment with Chenopodium album dry biomass and two Trichoderma species on growth of chickpea var. Noor 2009 in Sclerotium rolfsii contaminated soil

Quinoa ( Chenopodium quinoa L.) is a recently introduced pseudocereal crop in Pakistan. In the present study, methanolic extract was partitioned with n- hexane, chloroform and finally with ethyl acetate. The ethyl acetate fraction was subjected to GC-MS analysis for the identification of various antimicrobial and antioxidant constituents. Thirteen compounds were identified through GC-MS analysis of this fraction. Among these, 11 compounds possessed antibacterial, antifungal and/or antioxidant properties as reported in literature. These include naphthalene; tetradecane; hexadecane; pentadecane; cyclohexadecane; 1,2-benzenedicarboxylic acid, bis(2-methylpropyl) ester; dibutyl phthalate; 1-nonadecene; 1-octadecanol; 9-hexacosene; and 1,2-benzenedicarboxylic acid, mono(2-ethylhexyl) ester.

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Antifungal, antibacterial and antioxidant components of ethyl acetate extract of quinoa stem

Onion basal rot is the most destructive disease caused by Fusarium oxysporum f. sp. cepae (FOC) for onion growing regions of the world. To control this disease, biological control agents 287 phosph...

Biological control of onion basal rot disease using phosphate solubilising rhizobacteria

Onion is attacked by destructive soil-borne fungal plant pathogen Fusarium oxysporum f. sp. cepae, resulting in basal rot disease. In the present study, three Trichoderma species (T. pseudokoningii, T. harzianum and T. reesei) and leaves of solanaceous weed Withania somnifera were used for management of this disease. The in vitro interaction study revealed T. harzianum as the most effective biocontrol agent against the pathogen. In a pot trial, dried leaf material of W. somnifera (1%, 2% and 3% w/w) and inoculum of T. harzianum were mixed in the pot soil previously inoculated with the pathogen. The highest incidence of the disease (87%) was found in positive control (pathogen inoculation without any amendment). Different rates of dry leaf material reduced the incidence of the disease to 41-66%. T. harzianum in combination with leaf material reduced the incidence of the disease to 20-53%. In a laboratory bioassay, the dry leaf extract of W. somnifera was prepared in methanol and partitioned with n-hexane, chloroform, ethyl acetate and n-butanol. The highest concentration (200 mg mL-1) of all except for the n-butanol fraction significantly decreased fungal biomass over control. This study concludes that basal rot of onion can be controlled by combined application of W. somnifera dry leaf material and biological control agent T. harzianum.

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Biological Management of Basal Rot of Onion by Trichoderma harzianum and Withania somnifera

The present study was carried out to check the antifungal potential of Sisymbrium irio L. shoot extract against Fusarium oxysporum f. sp. cepae (FOC). In preliminary bioassays, different concentrations (1 to 5%) of leaf, stem and fruit extracts were evaluated against FOC. All the extracts were effective against the pathogen. However, the leaf extract was found the most effective causing 25-41% decrease in FOC biomass. The fractionation of methanolic leaf extract was done by two organic solvents namely n-hexane and chloroform. Different concentrations (1.56 to 200 mg mL-1) of these fractions were tested against FOC. The n-hexane and chloroform fractions showed inhibitory activity against the pathogen and resulted in 77-93% and 80-96% reduction in biomass of FOC, respectively. GC-MS analysis showed the presence of 24 compounds in n-hexane and 4 compounds in chloroform fraction. In n-hexane fraction, β-sitosterol (18.64%) was the most abundant compound followed by orotic acid, bis(tert-butyldimethylsilyl)-, tert-butyldimethylsilyl ester (12.18%), 10-octadecenoic acid, methyl ester (7.90%) and 1,2-benzenedicarboxylic acid, diisooctyl ester (6.05%). Major compounds identified in chloroform fraction were 1,3-benzenedicarboxylic acid, bis(2-ethylhexyl) ester (50.82%) and di-n-octyl phthalate (33.00%). This study concludes that n-hexane and chloroform fractions of methanolic leaf extract of S. irio contain potent antifungal constituents for the management of FOC.

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R. Akhtar

Papers

Biological Management of Basal Rot of Onion by Trichoderma harzianum and Withania somnifera

Bioactive Constituents of Shoot Extracts of Sisymbrium irio L. Against Fusarium oxysporum f. sp. cepae