Pathogenesis in Aspergillus Ear Rot of Maize: Light Microscopy of Fungal Spread from Wounds

Smart, M. G.; Wicklow, Donald T.; Caldwell, R. W.

doi:10.1094/phyto-80-1287

Cited by 71 publications

(48 citation statements)

References 14 publications

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“…Likewise, in nature, A. flavus can directly infect maize kernels under drought stress and high temperatures (32 to 36°C) known to compromise physiological defense systems as well as lead to cracks in the seed (16,21,30). In preliminary experiments we found that the condition of insect and plant material deteriorated considerably when maintained above 30°C.…”

Section: Discussionmentioning

confidence: 81%

Lack of Host Specialization inAspergillus flavus

Leger

Screen

Shams-Pirzadeh

2000

Appl Environ Microbiol

195

101

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Aspergillus spp. cause disease in a broad range of organisms, but it is unknown if strains are specialized for particular hosts. We evaluated isolates of Aspergillus flavus, Aspergillus fumigatus, and Aspergillus nidulans for their ability to infect bean leaves, corn kernels, and insects (Galleria mellonella). Strains of A. flavus did not affect nonwounded bean leaves, corn kernels, or insects at 22°C, but they killed insects following hemocoelic challenge and caused symptoms ranging from moderate to severe in corn kernels and bean leaves injured during inoculation. The pectinase P2c, implicated in aggressive colonization of cotton bolls, is produced by most A. flavus isolates, but its absence did not prevent colonization of bean leaves. Proteases have been implicated in colonization of animal hosts. All A. flavus strains produced very similar patterns of protease isozymes when cultured on horse lung polymers. Quantitative differences in protease levels did not correlate with the ability to colonize insects. In contrast to A. flavus, strains of A. nidulans and A. fumigatus could not invade living insect or plant tissues or resist digestion by insect hemocytes. Our results indicate that A. flavus has parasitic attributes that are lacking in A. fumigatus and A. nidulans but that individual strains of A. flavus are not specialized to particular hosts.Aspergillus species are associated with disease in plants, insects, man, and other animals (4, 14, 24). For example, Aspergillus flavus causes disease of agronomically important crops, such as corn and peanuts, is second only to Aspergillus fumigatus as the cause of human invasive aspergillosis, and is the Aspergillus species most frequently reported to infect insects.Aspergillus spp. are generally regarded as opportunistic pathogens that require wounds or otherwise weakened hosts for colonization (24). A. flavus, however, also has limited parasitic abilities and, in some cases, can directly invade seeds and colonize living tissues (20). We found previously (35) that Aspergillus spp. produced a much broader spectrum of protein and polysaccharide-hydrolyzing enzymes than did specialized pathogens, which may be indicative of their less-specialized lifestyle. Shieh et al. (29), however, found that aggressiveness toward cotton depended on production of a specific pectinase isoenzyme (P2c) that facilitates spread between cotton boll locules. Weakly pathogenic strains lack P2c, and their growth is limited to individual locules. Likewise, production of proteinases (elastases) in culture has been correlated with isolate virulence to mice and with isolation from human hosts with aspergillosis (12, 13, 25), although soil isolates also produce proteases (17). Proteases may be required for virulence to plants, as resistance to A. flavus in corn kernels derives from a protease inhibitor (5).Populations of A. flavus are highly polymorphic and complex (40), but we do not know if specialized subspecies or physiological races contribute to the broad host range (1, 6, 9). If specializat...

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Section: Discussionmentioning

confidence: 81%

Lack of Host Specialization inAspergillus flavus

Leger

Screen

Shams-Pirzadeh

2000

Appl Environ Microbiol

195

101

View full text Add to dashboard Cite

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“…Host lipid reserves are depleted during seed colonization by Aspergillus (23,37), with lipase and esterase activities implicated in seed pathogenesis (37,39). Both null mutants were impaired in seed colonization, where neither strain could degrade lipid reserves despite hyphal penetration of at least some layers of the host seeds (Fig.…”

Section: Discussionmentioning

confidence: 98%

Distinct Roles for VeA and LaeA in Development and Pathogenesis ofAspergillus flavus

Amaike¹,

2009

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Aspergillus flavus, a mycotoxigenic filamentous fungus, colonizes several important agricultural crops, such as maize and peanuts. Two proteins, VeA and LaeA, known to form a nuclear complex in Aspergillus nidulans have been found to positively regulate developmental processes in several Aspergillus species. Here, an examination of near-isogenic A. flavus mutants differing in copy number of veA and laeA alleles (0, 1, or at least 2 each) revealed critical roles for VeA and LaeA in A. flavus development and seed colonization. In contrast to the wild type, both null mutants were unable to metabolize host cell lipid reserves and were inhibited by oleic acid in growth assays. The copy number of LaeA but not VeA appeared critical for a density-dependent sclerotial-to-conidial shift, since the multicopy laeA (MClaeA) strain produced relatively constant sclerotial numbers with increasing population size rather than showing the decrease in sclerotia seen in both the wild-type and MCveA strains. The MCveA-laeA strain yielded an intermediate phenotype. This study revealed unique roles of VeA and LaeA in seed pathogenesis and fungal biology, distinct from their cooperative regulatory functions in aflatoxin and sclerotial development.

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“…There are several ways by which natural A. flavus infection in maize cobs can take place. Infection can occur through the silk and in this case A. flavus propagules are mainly superficial to maize kernel (Marsh & Payne, 1984a, 1984b, through the cob with access to the kernel through the spikelet (Smart et al, 1990). It can also be introduced and spread by cob borers and other insects (Drepper & Renfro, 1990;Beti et al 1995).…”

Section: Discussionmentioning

confidence: 99%

Effects of variety, cropping system and soil inoculation with Aspergillus flavus on aflatoxin levels during storage of maize

Tédihou

Olatinwo

Hell

et al. 2012

Trop. plant pathol.

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The effects of soil inoculation with A. flavus, variety and cropping system on the level of aflatoxin in stored maize were investigated under crop storage conditions in Benin. The experiment was organized in a factorial scheme (two varieties x two cropping system x with or without A. flavus soil inoculation) with eight treatments carried out in a completely randomized block design with three replications. A. flavus incidence in the plots soil was assessed both before and after soil inoculation. The harvested maize was stored for four months and cobs were sampled in a monthly interval and analyzed for the determination of Fusarium spp. colonization, Penicillium spp. and A. flavus cfu levels, insect pests population size and aflatoxin content. Multi-factorial analysis of variance and linear regression analyses with dummy variables were used to compare treatments. The concentrations of aflatoxin B 1 and B 2 in the kernels tended to increase with time during storage. Variety and fungal inoculation were the main factors influencing the levels of aflatoxins in stored maize. The improved variety showed a higher number of A. flavus cfu and aflatoxin B 1 and B 2 levels as compared to the local variety. Intercropping with Vigna unguiculata decreased the aflatoxin concentration in the improved variety but not in the local variety. The local variety had higher levels of Penicillium spp. and lower levels of Fusarium spp. than the improved variety. The treatments had no effect on the populations of the most common storage insect pests, but their levels were positively correlated with aflatoxin content. Both the initial inoculum level and the variety effect on the water content of the kernels after harvest played a significant role in A. flavus infection.

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Pathogenesis in Aspergillus Ear Rot of Maize: Light Microscopy of Fungal Spread from Wounds

Cited by 71 publications

References 14 publications

Lack of Host Specialization inAspergillus flavus

Lack of Host Specialization inAspergillus flavus

Distinct Roles for VeA and LaeA in Development and Pathogenesis ofAspergillus flavus

Effects of variety, cropping system and soil inoculation with Aspergillus flavus on aflatoxin levels during storage of maize

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