Aspergillus Flavus Invasion Research Articles

In vitro Varietal Screening for Resistance to Aspergillus Flavus Invasion and Aflatoxin Production in Groundnut

In vitro Varietal Screening for Resistance to Aspergillus Flavus Invasion and Aflatoxin Production in Groundnut

Potential involvement of Aspergillus flavus laccases in peanut invasion at low water potential

Aspergillus flavus accumulates carcinogenic aflatoxins in peanuts, mainly in immature kernels during drought. Aspergillus flavus invasion induces accumulation of phytoalexins, mostly stilbenoids in peanut, as a plant defence mechanism. Because fungal laccases are often related to pathogenicity and can degrade stilbenoids, this study reports for the first time the expression of A. flavus laccases in the presence of kernels, hulls and low water potential in relation to the accumulation of phytoalexins in peanut kernels. Packed‐cell volume (PCV) of A. flavus biomass was significantly higher (P ≤ 0·01) in the presence of mature kernels, dead kernels, and mature and immature peanut hulls than the control. The presence of kernels and hulls lowered the level of expression of three A. flavus laccases by 4–6‐fold (P < 0·01), whereas 3% sucrose up‐regulated them by 35–304‐fold, and low water potential (−1·1 MPa) up‐regulated them by 85–248‐fold (P < 0·01). Phytoalexins that accumulated in peanut kernels in the presence of A. flavus and were quantified by HPLC‐DAD‐MS were primarily the stilbenoids: 3′‐isopentadienyl‐3,5,4′‐trihydroxystilbene (IPD), chiricanine‐A, arachidin‐2, arachidin‐3 and arahypin‐1. Apparent degradation of phytoalexins was observed when using a priori induction of phytoalexins in seeds in combination with a priori induction of laccases in A. flavus. The up‐regulation of laccase expression observed at −1·1 MPa and at high sucrose concentration could be contributing to peanut invasion in immature kernels under drought conditions.

Overexpression of ARAhPR10, a Member of the PR10 Family, Decreases Levels of <i>Aspergillus flavus</i> Infection in Peanut Seeds

Peanut (Arachis hypogaea L.) is one of the most susceptible host crops to Aspergillus flavus invasion and subsequent aflatoxin contamination. In this report, a new member of PR10 family putative resistant gene (designated as ARAhPR10, No. EU661964.1) encoding a PR10 protein was isolated and characterized. Analysis of qRT-PCR showed that the expression of ARAhPR10 was induced by pre-harvested A. flavus infection, but no significant difference was observed between resistant genotype “GT-C20” and susceptible genotype “Yueyou 7”. Seven transgenic peanut lines expressing the ARAhPR10 gene under the control of 35S promoter were obtained using the Agrobacterium tumefaciens-mediated method. Real time RT-PCR results showed that the expression level of the ARAhPR10 was significantly higher and the A. flavus infection and aflatoxin content were significantly lower in seeds of transgenic lines than that of the wild type. A significant negative correlation between ARAhPR10 expression at transcript level and seeds aflatoxin production was observed. Combining the previous results, it is suggested that ARAhPR10 expression play an important role in peanut host resistance to A. flavus infection and aflatoxin producing.

Pre-harvest aflatoxin contamination and soluble sugars of peanut

Peanut (Arachis hypogaea L.) is an important commercial crop throughout the world and is one of the most susceptible crops to Aspergillus flavus invasion (Guo et al., 2009)

Development and Evaluation of Peanut Germplasm with Resistance to <I>Aspergillus flavus</I> from Core Collection

Peanut (Arachis hypogaea L.), one of the main oil and cash crops in the world, is easily susceptible to Aspergillus flavus, resulting huge loss in its quality, so Aspergillus flavus infection greatly limits peanut production and industry in China. Therefore, it is imperative to develop new peanut germplasm with resistance to Aspergillus flavus in breeding program. The core collection is well accepted as a useful way to improve the efficiency of crop germplasm evaluation and utilization, which contains a subset of accessions from the entire collection that covers the most of available genetic information. In the present study, a total of 561 accessions of Chinese peanut core collection and 155 accessions of ICRISAT mini core collection were identified. Eight varieties with resistance to Aspergillus flavus invasion and aflatoxin production each were developed, including one (51002-6) with elite agronomic traits. The peanut germplasm with resistance to Aspergillus flavus invasion and aflatoxin production in ICRISAT mini core were more than those in Chinese peanut core collection. In addition, the percentages of accessions with resistance to Aspergillus flavus invasion in var. hypogaea, and accessions resistant to aflatoxin production in var. hirsuta were relatively high in comparison with others. Genetic diversity in the resistant peanut selections was evaluated based on morphological traits and SSR approach. ICG12625 with resistance to aflatoxin production and ICG4750 with resistance to aflatoxin invasion were evaluated by SSR, the genetic distance of them with high-yielding cultivars such as Zhonghua 5, Zhonghua 6 and Zhonghua 12 and Yuanza 9102 was larger. The primers were designed based on the conserved NBS-LRR domains of the disease resistance genes sequence, one RGA (Resistance gene analog) from genomic DNA of six different peanuts with resistance to Aspergillus flavus was obtained through PCR.

Overview of Research Progress on Peanut (Arachis hypogaea L.) Host Resistance to Aflatoxin Contamination and Genomics at the Guangdong Academy of Agricultural Sciences

Abstract Aflatoxin contamination in peanut is a serious and world-wide problem concerning food safety and human health. Plant-host resistance is a highly desirable tactic that can be used to manage this problem. This review summarizes research progress in peanut host resistance mechanisms to aflatoxin contamination at the Crops Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, China. Through systematic resistance evaluations, germplasm lines resistant to Aspergillus flavus invasion have been identified and two resistant cultivars were developed and released in South China. The resistance has been associated with testa wax and presence of cutin layer, active oxygen and membrane lipid peroxidation, phytoalexin accumulation, and antifungal proteins in the peanut kernels. Functional genomics will be a valuable tool to understand the comprehensive mechanisms governing the resistance pathways. In this paper we also summarized the advances made by our group in the area of genomic research, especially in mining EST-SSRs, development of a genetic linkage map and QTLs mapping in the cultivated peanut species.

Evaluation of selected geocarposphere bacteria for biological control of Aspergillus flavus in peanut

Selected bacterial strains isolated from the region of peanut pod development (geocarposphere) and two additional bacterial strains were screened as potential biological control agents against Aspergillus flavus invasion and subsequent aflatoxin contamination of peanut in laboratory, greenhouse, and field trials. All 17 geocarposphere strains tested delayed invasion of young roots and reduced colonization by the fungus in a root-radicle assay used as a rapid laboratory prescreen. In a greenhouse study, seven bacterial strains significantly reduced pod colonization by A. flavus compared to the control. In a field trial, conducted similarly to the greenhouse assay, pods sampled at mid-peg from plants seed-treated with suspensions of either 91A-539 or 91A-550 were not colonized by A. flavus, and the incidence of pods invaded from plants treated with either 91A-539 or 91A-599 was consistently lower than nonbacterized plants at each of five sampling dates. At harvest, 8 geocarposphere bacterial strains significantly lowered the percentage of pods colonized (> 51%) compared to the control. Levels of seed colonization ranged from 1.3% to 45% and did not appear related to aflatoxin concentrations in the kernels.

A low-cost microcomputer system to monitor and control an environmental control plot facility

Since 1980, six 67.1-m 2 environmental control plots with apparatus for soil temperature manipulation and motorized shelters for rainfall exclusion have been used for the study of Aspergillus flavus invasion and aflatoxin contamination of peanuts during drought stress. Manual controls and the absence of an alarm system for the plots have mandated daily monitoring and adjustments of thermostats for soil temperature control and visual inspection for proper shelter operation, especially during severe thunderstorms. Prior to 1987 experiments, a microcomputer-based control system was assembled to control the operation of the facility and provide telephone alarms for soil temperature discrepancies, improper shelter operation, or electrical power interruptions. Commercially available components were used to construct the system which cost approximately US$2000. At the end of a 50-day evaluation period, the system had provided an average plot soil temperature of 27.4°C with a setting of 26.7°C. The 95% confidence interval for the treatment period average during the tests was between 25.9°C and 27.9°C. Alarm annunciation and telephone notification were also provided as expected in response to plot temperature extremes and a power outage.

Susceptibility of Freshly Picked Ear Corn to Invasion by Fungi1

High-moisture ear corn held 9 days at 23 C remained free of visible mold or evidence of Aspergillus flavus invasion provided there was no mechanical damage of the kernels.