Effect of Carotenoids on Aflatoxin B(1) Synthesis by Aspergillus flavus

ABSTRACT Carotenes and xanthophylls occurring in yellow corn and related terpenoids were tested for their effect on growth and aflatoxin B(1) production by Aspergillus flavus NRRL 3357, using the suspended disc culture method. Aflatoxin synthesis was inhibited at concentrations of beta-carotene, lutein, and zeaxanthin comparable to those found in the horny endosperm of mature corn. Usually growth was not significantly affected. Inhibition of aflatoxin biosynthesis was greater for compounds with an alpha-ionone-type ring (alpha-carotene, lutein, or alpha-ionone) compared with compounds with a beta-ionone ring. The presence of hydroxy groups on the rings tended to decrease inhibition, but did not override the effect of the ring type; lutein was similar to alpha-carotene and zeaxanthin was similar to beta-carotene in inhibition. A mutant accumulating norsolorinic acid (NA), A. parasiticus SRRC 162, incubated with alpha-carotene produced reduced levels of both NA and aflatoxin, indicating that inhibition occurred before NA. Additional A. flavus strains tested against 50 mug/ml of beta-carotene had 89 to 96% inhibition, which was significantly more sensitive than NRRL 3357. A. parasiticus strains were less sensitive and generally had similar or lower inhibition than NRRL 3357. The results indicate that the presence of carotenoids in endosperm may decrease the amount of aflatoxin produced by A. flavus.     

beta-1,3-Glucanase Activity in Peanut Seed (Arachis hypogaea) is Induced by Inoculation with Aspergillus flavus and Copurifies with a Conglutin-Like Protein

ABSTRACT Infection of peanut (Arachis hypogaea) seed by Aspergillus flavus and A. parasiticus is a serious problem that can result in aflatoxin contamination in the seed. Breeding resistant cultivars would be an effective approach to reduce aflatoxin accumulation. The objective of this study was to investigate the expression of the pathogenesis-related (PR) protein beta-1,3-glucanase and the isoform patterns in peanut seed inoculated with A. flavus. Peanut genotypes GT-YY9 and GT-YY20 (both resistant to A. flavus infection) and Georgia Green and A100 (both susceptible to A. flavus infection) were used in this study. The activities of beta-1,3-glucanase were similar in the uninfected seed of all genotypes, but increased significantly in the resistant genotypes after inoculation in comparison with the susceptible genotypes. An in-gel (native polyacrylamide gel electrophoresis [PAGE]) enzymatic activity assay of beta-1,3-glucanase revealed that there were more protein bands corresponding to beta-1,3-glucanase isoforms in the infected seed of resistant genotypes than in the infected seed of susceptible genotypes. Both acidic and basic beta-1,3-glucanase isoforms were detected in the isoelectric focusing gels. Thin-layer chromatography analysis of the hydrolytic products from the reaction mixtures of the substrate with the total protein extract or individual band of native PAGE revealed the presence of enzymatic hydrolytic oligomer products. The individual bands corresponding to the bands of beta-1,3-glucanase isoforms Glu 1 to 5 were separated on the sodium dodecyl sulfate-PAGE, resulting in two bands of 10 and 13 kDa, respectively. The sequences of fragments of the 13-kDa major protein band showed a high degree of homology to conglutin, a storage protein in peanut seed. Conglutin is reported as a peanut allergen, Ara h2. Our data provide the first evidences for peanut having beta-1,3-glucanase activities and the association with the resistance to A. flavus colonization in peanut seed. We have not directly demonstrated that conglutin has beta-1,3-glucanase activity.     

Amy1, the alpha-Amylase Gene of Aspergillus flavus: Involvement in Aflatoxin Biosynthesis in Maize Kernels

ABSTRACT Aspergillus flavus is the causal agent of an ear and kernel rot in maize. In this study, we characterized an alpha-amylase-deficient mutant and assessed its ability to infect and produce aflatoxin in wounded maize kernels. The alpha-amylase gene Amy1 was isolated from A. flavus, and its DNA sequence was determined to be nearly identical to Amy3 of A. oryzae. When Amy1 was disrupted in an aflatoxigenic strain of A. flavus, the mutant failed to produce extracellular alpha-amylase and grew 45% the rate of the wild-type strain on starch medium. The mutant produced aflatoxin in medium containing glucose but not in a medium containing starch. The alpha-amylase-deficient mutant produced aflatoxin in maize kernels with wounded embryos and occasionally produced aflatoxin only in embryos of kernels with wounded endosperm. The mutant strain failed to produce aflatoxin when inoculated onto degermed kernels. In contrast, the wild-type strain produced aflatoxin in both the endosperm and embryo. These results suggest that alpha-amylase facilitates aflatoxin production and growth of A. flavus from a wound in the endosperm to the embryo. A 14-kDa trypsin inhibitor associated with resistance to A. flavus and aflatoxin in maize also inhibited the alpha-amylase from A. flavus, indicating that it is a bifunctional inhibitor. The inhibitor may have a role in resistance, limiting the growth of the fungus in the endosperm tissue by inhibiting the degradation of starch.     

A Chitinase from Tex6 Maize Kernels Inhibits Growth of Aspergillus flavus

ABSTRACT The maize inbred Tex6 has resistance to colonization and aflatoxin accumulation by Aspergillus flavus. A protein inhibitory to growth of A. flavus has been identified from aqueous extracts of mature Tex6 seeds. This study reports the purification of a chitinase associated with this inhibitory activity to electrophoretic homogeneity and the further characterization of its properties. The inhibitory protein, which has an M(r) of 29,000, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, is an endochitinase that is also capable of exochitinase activity. The enzyme has an optimal pH of 5.5 and a temperature optimum of 45 degrees C. Chitinase activity in maize kernels peaked approximately 36 days after pollination. The Tex6 chitinase purified in this study is capable of inhibiting the growth of A. flavus by 50% at a concentration of 20 mug/ml. Our data indicate that chitinase activity in Tex6 kernels makes a major contribution to the antifungal activity in this maize genotype. Partial peptide sequence of the chitinase showed it to differ from previously reported chitinases.     

Tissue-specific components of resistance to Aspergillus ear rot of maize

Aspergillus flavus and other Aspergillus spp. infect maize and produce aflatoxins. An important control measure is the use of resistant maize hybrids. There are several reports of maize lines that are resistant to aflatoxin accumulation but the mechanisms of resistance remain unknown. To gain a better understanding of resistance, we dissected the phenotype into 10 components: 4 pertaining to the response of silk, 4 pertaining to the response of developing kernels, and 2 pertaining to the response of mature kernels to inoculation with A. flavus. In order to challenge different tissues and to evaluate multiple components of resistance, various inoculation methods were used in experiments in vitro and under field conditions on a panel of diverse maize inbred lines over 3 years. As is typical for this trait, significant genotype-environment interactions were found for all the components of resistance studied. There was, however, significant variation in maize germplasm for susceptibility to silk and kernel colonization by A. flavus as measured in field assays. Resistance to silk colonization has not previously been reported. A significant correlation of resistance to aflatoxin accumulation with flowering time and kernel composition traits (fiber, ash, carbohydrate, and seed weight) was detected. In addition, correlation analyses with data available in the literature indicated that lines that flower later in the season tend to be more resistant. We were not able to demonstrate that components identified in vitro were associated with reduced aflatoxin accumulation in the field.     

A Corn Trypsin Inhibitor with Antifungal Activity Inhibits Aspergillus flavus alpha-Amylase

ABSTRACT In this study, we found that the inhibition of fungal growth in potato dextrose broth (PDB) medium by the 14-kDa corn trypsin inhibitor (TI) protein, previously found to be associated with host resistance to aflatoxin production and active against various fungi, was relieved when exogenous alpha-amylase was added along with TI. No inhibitory effect of TI on fungal growth was observed when Aspergillus flavus was grown on a medium containing either 5% glucose or 1% gelatin as a carbon source. Further investigation found that TI not only inhibited fungal production of extracellular alpha-amylase when A. flavus was grown in PDB medium containing TI at 100 mug ml(-1) but also reduced the enzymatic activity of A. flavus alpha-amylase by 27%. At a higher concentration, however, TI stimulated the production of alpha-amylase. The effect of TI on the production of amyloglucosidase, another enzyme involved in starch metabolism by the fungus, was quite different. It stimulated the production of this enzyme during the first 10 h at all concentrations studied. These studies suggest that the resistance of certain corn genotypes to A. flavus infection may be partially due to the ability of TI to reduce the production of extracellular fungal alpha-amylase and its activity, thereby limiting the availability of simple sugars for fungal growth. However, further investigation of the relationship between TI levels and fungal alpha-amylase expression in vivo is needed.     

Corn Seed Proteins Inhibitory to Aspergillus flavus and Aflatoxin Biosynthesis

ABSTRACT This study reports the presence of two fractions from corn seeds inhibitory to aflatoxin formation. Using a sensitive laboratory assay that can measure both inhibition of fungal growth and inhibition of aflatoxin biosynthesis, we examined aqueous extracts from seeds of Tex6, a corn inbred shown to be highly resistant to aflatoxin accumulation in field and laboratory evaluations. In these extracts, we identified two biologically active fractions. One inhibited growth of Aspergillus flavus and, thus, aflatoxin accumulation, and the other inhibited aflatoxin formation with little effect on fungal growth. The compounds responsible for these activities appear to be proteaceous, as they are water soluble, heat labile, and sensitive to proteinase K treatment. The compounds were partially purified by ultrafiltration and chromatography. The estimated molecular mass of the growth inhibitor is approximately 28 kDa, and that of the aflatoxin biosynthesis inhibitor appears to be greater than 100 kDa. Partially purified preparations of the growth inhibitor and aflatoxin biosynthesis inhibitor cause 50% inhibition at 26 and 75 mug of protein/ml, respectively. The presence of these compounds in Tex6 may explain its resistance to aflatoxin accumulation.     

Inducers of Aflatoxin Biosynthesis from Colonized Maize Kernels Are Generated by an Amylase Activity from Aspergillus flavus

ABSTRACT Aflatoxin biosynthesis was induced by compounds in filtrates (EF) obtained from cultures consisting of ground maize kernels colonized by Aspergillus flavus. The inducing activity increased to a maximum at 4 days of incubation and then decreased. Amylase activity was detected in the EF, suggesting that the inducers are products of starch degradation (glucose, maltose, and maltotriose). Analysis of the enzyme by isoelectric focusing electrophoresis indicated a single alpha-amylase with a pI of 4.3. No maltase or amyloglucosidase was detected in the EF. High-pressure liquid chromatography analysis of the EF indicated the presence of glucose, maltose, and maltotriose in near-equal molar concentrations (about 15 mM). With a beta-glucuronidase (GUS) reporter assay consisting of A. flavus transformed with an aflatoxin gene promoter-GUS reporter gene fusion to monitor induction of aflatoxin biosynthesis, the minimum concentration of glucose, maltose, or maltotriose that induced measurable GUS activity was determined to be 1 mM. These results support the hypothesis that the best inducers of aflatoxin biosynthesis are carbon sources readily metabolized via glycolysis. They also suggest that alpha-amylase produced by A. flavus has a role in the induction of aflatoxin biosynthesis in infected maize kernels.     

Stable oxygen-hydrogen isotopes reveal water use strategies of Tamarix taklamakanensis in the Taklimakan Desert,China

Tamarix taklamakanensis,a dominant species in the Taklimakan Desert of China,plays a crucial role in stabilizing sand dunes and maintaining regional ecosystem stability.This study aimed to determine the water use strategies of T.taklamakanensis in the Taklimakan Desert under a falling groundwater depth.Four typical T.taklamakanensis nabkha habitats(sandy desert of Tazhong site,saline desert-alluvial plain of Qiemo site,desert-oasis ecotone of Qira site and desert-oasis ecotone of Aral site)were selected with different climate,soil,groundwater and plant cover conditions.Stable isotope values of hydrogen and oxygen were measured for plant xylem water,soil water(soil depths within 0–500 cm),snowmelt water and groundwater in the different habitats.Four potential water sources for T.taklamakanensis,defined as shallow,middle and deep soil water,as well as groundwater,were investigated using a Bayesian isotope mixing model.It was found that groundwater in the Taklimakan Desert was not completely recharged by precipitation,but through the river runoff from snowmelt water in the nearby mountain ranges.The surface soil water content was quickly depleted by strong evaporation,groundwater depth was relatively shallow and the height of T.taklamakanensis nabkha was relatively low,thus T.taklamakanensis primarily utilized the middle(23%±1%)and deep(31%±5%)soil water and groundwater(36%±2%)within the sandy desert habitat.T.taklamakanensis mainly used the deep soil water(55%±4%)and a small amount of groundwater(25%±2%)within the saline desert-alluvial plain habitat,where the soil water content was relatively high and the groundwater depth was shallow.In contrast,within the desert-oasis ecotone in the Qira and Aral sites,T.taklamakanensis primarily utilized the deep soil water(35%±1%and 38%±2%,respectively)and may also use groundwater because the height of T.taklamakanensis nabkha was relatively high in these habitats and the soil water content was relatively low,which is associated with the reduced groundwater depth due to excessive water resource exploitation and utilization by surrounding cities.Consequently,T.taklamakanensis showed distinct water use strategies among the different habitats and primarily depended on the relatively stable water sources(deep soil water and groundwater),reflecting its adaptations to the different habitats in the arid desert environment.These findings improve our understanding on determining the water sources and water use strategies of T.taklamakanensis in the Taklimakan Desert.     

Damage by wind-blown sand and its control measures along the Taklimakan Desert Highway in China

Desertification is one of the most serious environmental problems in the world,especially in the arid desert regions.Combating desertification,therefore,is an urgent task on a regional or even global scale.The Taklimakan Desert in China is the second largest mobile desert in the world and has been called the'Dead Sea'due to few organisms can exist in such a harsh environment.The Taklimakan Desert Highway,the longest desert highway(a total length of 446 km)across the mobile desert in the world,was built in the 1990s within the Taklimakan Desert.It has an important strategic significance regarding oil and gas resources exploration and plays a vital role in the socio-economic development of southern Xinjiang,China.However,wind-blow sand seriously damages the smoothness of the desert highway and,in this case,mechanical sand control system(including sand barrier fences and straw checkerboards)was used early in the life of the desert highway to protect the road.Unfortunately,more than 70%of the sand barrier fences and straw checkerboards have lost their functions,and the desert highway has often been buried and frequently blocked since 1999.To solve this problem,a long artificial shelterbelt with the length of 437 km was built along the desert highway since 2000.However,some potential problems still exist for the sustainable development of the desert highway,such as water shortage,strong sandstorms,extreme environmental characteristics and large maintenance costs.The study aims to provide an overview of the damages caused by wind-blown sand and the effects of sand control measures along the Taklimakan Desert Highway.Ultimately,we provide some suggestions for the biological sand control system to ensure the sustainable development of the Taklimakan Desert Highway,such as screening drought-resistant species to reduce the irrigation requirement and ensure the sound development of groundwater,screening halophytes to restore vegetation in the case of soil salinization,and planting cash crops,such as Cistanche,Wolfberry,Apocynum and other cash crops to decrease the high cost of maintenance on highways and shelterbelts.     

Efficacy of certain agrochemicals on Aspergillus spp. and subsequent aflatoxin production in rice

Efficacy of certain fungicides and non-conventional chemicals against Aspergillus spp. contamination and subsequent aflatoxin production in rice was investigated. Among the 10 fungicides tested, carbendazim, contaf plus, folicur, propiconazole and saaf completely inhibited the growth of all Aspergillus spp. and aflatoxin B₁ (AFB1) production at 1 g or ml/kg concentration. Of the five non-conventional chemicals tested, benzoic acid effectively inhibited the mycelial growth of Aspergillus flavus (72%) at 4 g/kg, completely inhibited the Aspergillus parasiticus and Aspergillus niger even at 1 g/kg and Aspergillus ochraceus at 4 g/kg concentration. Vanillin completely reduced the AFB1 production at 4 g/kg of seed followed by sodium chloride with out inhibiting the mycelial growth. This study reveals that fungicides and non-conventional chemicals had effectively inhibited the mycelial growth of Aspergillus spp. and AFB1 production in rice.     

Spatial Relationships of Soil Texture and Crop Rotation to Aspergillus flavus Community Structure in South Texas

ABSTRACT Aspergillus flavus, the causal agent of aflatoxin contamination of cottonseed, is a natural inhabitant of soils. A. flavus can be divided into the S and L strains, of which the S-strain isolates, on average, produce greater quantities of aflatoxins than the L-strain isolates. Aflatoxin contamination can be severe in several crops in South Texas. The structure of A. flavus communities residing in soils of South Texas was determined from 326 soil samples collected from 152 fields located from the Rio Grande Valley in the south to Fort Bend County in the north from 2001 through 2003. Analysis of variance indicated significant differences in the incidence of A. flavus isolates belonging to the S strain (percent S) among regions. The Coastal Bend (30.7%) and Upper Coast (25.5%) regions had significantly higher percent S incidence than the Rio Grande Valley (4.8%). No significant differences in percent S among years were detected. The CFU per gram of soil were not significantly different among regions. Strain S incidence was positively correlated with clay content and negatively correlated with sand content. Fields cropped to cotton the previous year had a higher S-strain incidence, whereas fields cropped to corn had greater total quantities of A. flavus propagules. Maps of S-strain patterns show that the S strain constitutes >30% of the overall A. flavus community in the area extending from the central Coastal Bend region to the central Upper Coast region. The west Rio Grande Valley had the lowest S-strain incidence (<10%). Geographic variation in S-strain incidence may influence the distribution of aflatoxin contamination in South Texas.     

2000-2018年古尔班通古特沙漠EVI时空变化特征

基于MODIS-EVI数据,采用一元线性回归、经验正交函数(EOF)、变异系数,从时间和空间2个维度分析古尔班通古特沙漠增强型植被指数(EVI)的时空变化特征。结果表明:2000—2018年古尔班通古特沙漠整体EVI的年际变化呈显著增加趋势,增长速率为0. 016 0·(10a)~(-1)(P 0. 01),其中固定沙丘、半固定沙丘和流动沙丘中的EVI年际变化也呈显著增加趋势;生长季内沙漠整体及不同类型EVI的变化趋势大致相同,从3月开始,EVI逐渐增加,并在6—7月达到一年中的最高值;古尔班通古特沙漠大部分区域的EVI呈上升趋势,上升趋势明显的区域主要集中在沙漠南缘以及沙漠西缘的开荒区域,沙漠腹地EVI上升趋势较小,EVI降低的区域主要分布在沙漠北部;古尔班通古特沙漠EVI波动较大的区域在沙漠西缘与南缘,其中波动最大的区域在沙漠西缘的开荒区域,沙漠腹地EVI波动较小。EVI能够较好地反映以固定和半固定为主的沙漠区植被覆盖变化,其反映的植被状况对区域沙漠地貌类型的空间划分具有重要的参考意义。     

Advances in the Development of Host Resistance in Corn to Aflatoxin Contamination by Aspergillus flavus

ABSTRACT Aflatoxins are toxic, highly carcinogenic secondary metabolites of Aspergillus flavus and A. parasiticus, which when produced during fungal infection of a susceptible crop in the field or after harvest contaminate food and feed and threaten human and animal health. Although there are several management strategies that may reduce aflatoxin contamination of corn, the preeminent strategy for elimination of aflatoxin is to develop preharvest host resistance to aflatoxin accumulation. This strategy has gained even greater prominence due to recent discoveries of natural resistance in corn that can be exploited in plant-breeding strategies. The ability to identify resistant corn genotypes has been enhanced by the development of a laboratory kernel-screening assay and by a strain of A. flavus genetically engineered to produce beta-glucuronidase, an enzyme whose activity can be monitored to assess the degree of fungal infection in kernels. Investigations of resistant corn genotypes have associated kernel pericarp wax characteristics with resistance, identified kernel proteins associated with resistance to and inhibition of fungal growth or aflatoxin biosynthesis, and identified chromosome regions associated with resistance to Aspergillus ear rot and aflatoxin production. Such research advances could lead, in the near future, to commercially available, agronomically acceptable corn lines with multiple preharvest resistances to aflatoxin contamination.     

Comparison of soil and corn kernel Aspergillus flavus populations: evidence for niche specialization

Aspergillus flavus is considered a generalist-opportunistic pathogen, but studies are beginning to show that A. flavus populations have strains specific to various hosts. The research objective was to determine whether A. flavus soil populations consist of solely saprophytic strains and strains which can be facultatively parasitic on corn. A. flavus was isolated from both corn kernels and soil within 11 Louisiana fields. Sixteen vegetative compatibility groups (VCGs) were identified among 255 soil isolates. Only 6 of the 16 VCGs were identified in the 612 corn isolates and 88% of corn isolates were in two VCGs, whereas only 5% of soil isolates belonged to the same two VCGs. Isolates were characterized for aflatoxin B1 production and sclerotial size. A random subset of the isolates (99 from corn and 91 from soil) were further characterized for simple-sequence repeat (SSR) haplotype and mating type. SSR polymorphisms revealed 26 haplotypes in the corn isolates and 78 in the soil isolates, and only 1 haplotype was shared between soil and corn isolates. Corn and soil populations were highly significantly different for all variables. Differences between corn and soil populations indicate that some soil isolates are not found in corn and some isolates have become specialized to infect corn. Further understanding of A. flavus virulence is important for development of resistant hybrids and for better biological control against toxigenic A. flavus.     

Spatial distribution of Aspergillus flavus and its toxigenic strains on commercial cottonseed from south Texas and its relationship to aflatoxin contamination

The structure of Aspergillus flavus communities associated with south Texas cottonseed was determined by analysing samples from 178 truckloads of commercial cottonseed from 35 gins, extending from Fort Bend County in the north to the Rio Grande Valley in the south, from September 1999 to October 2001. The number of colony-forming units (CFU) of A. flavus on the cottonseed, and the percentage of S strain (%S) were both correlated with aflatoxin contamination of cottonseed. The number of CFU differed between both regions and seasons, while %S differed only between regions. Comparison of maps of CFU and %S revealed that CFU shows a higher variation across years, while %S shows higher spatial variation. The Rio Grande Valley had significantly lower CFU and %S strain than the Coastal Bend and Upper Coast regions. Cottonseed produced in 1999 had significantly more A. flavus than that produced in either 2000 or 2001. Identification of factors dictating geographical variation in S-strain incidence may provide insights that will lead to improved aflatoxin management.     

入侵植物黄花刺茄(Solanum rostratum Dunal.)在新疆的分布及其群落特点

黄花刺茄原产北美,2005年首次在新疆乌鲁木齐县萨尔达坂乡和昌吉市三工镇发现。采用样方法,对不同生境中黄花刺茄分布相对集中的14个样地所有物种的多度、频度和重要值进行观测和分析,进一步明确黄花刺茄在新疆的分布区及其群落特征,并揭示其最适生境。结果表明：黄花刺茄分布于新疆乌鲁木齐市(县)、昌吉市、石河子市、吐鲁番市和托克逊县,分布在海拔-12～1 325 m处。生境类型包括荒漠草原、荒漠和绿洲。在3种生境中,黄花刺茄的相对多度均处于首位,且在绿洲中达到最大值,是入侵区域最为重要的物种;在相对盖度上均为第一,且绿洲(54.27％)＞荒漠草原(35.07％)＞荒漠(26.40％)。基于重要值数据的分析表明,黄花刺茄在3种生境中的综合适应力均最大,且以绿洲中尤为突出,表明黄花刺茄在新疆荒漠草原和荒漠生境中尚处于局部危害阶段,但在绿洲中已处于蔓延期。     

Control of Aspergillus growth and aflatoxin production using natural maize phytochemicals under different conditions of water activity

The effects of the natural phytochemicals trans-cinnamic acid (CA) and ferulic acid (FA) alone at concentrations of 1-25 mM and in 16 combinations (M: mixtures) on growth and aflatoxin B(1) production by Aspergillus flavus Link and A. parasiticus Speare were evaluated. Studies on growth rate and aflatoxin B(1) production were carried out in vitro in relation to a water activity a(w) of 0.999, 0.971, 0.955 and 0.937. Overall, CA at concentrations of 10 and 20 mM and FA-CA mixtures M3 (20 + 5 mM respectively), M8 (25 + 5 mM), M9 (1 + 10 mM), M10 (10 + 10 mM), M11 (20 + 10 mM), M12 (25 + 10 mM), M13 (1 + 20 mM), M14 (10 + 20 mM), M15 (20 + 20 mM) and M16 (25 + 20 mM) were the treatments most effective at inhibiting growth of the four species assayed. All strains were much more sensitive to all natural phytochemicals tested on growth rate at a(w) = 0.937. CA and the FA-CA mixtures M1 (1 + 1 mM respectively), M4 (25 + 1 mM), M5 (1 + 5 mM), M6 (10 + 1 mM), M7 (20 + 1 mM), M8 (25 + 5 mM), M9 (1 + 10 mM), M10 (10 + 10 mM), M11 (20 + 10 mM), M12 (25 + 10 mM), M13 (1 + 20 mM), M14 (10 + 20 mM), M15 (20 + 20 mM) and M16 (25 + 20 mM) completely inhibited aflatoxin B(1) production by all strains at a(w) = 0.999, 0.971, 0.955 and 0.937. Decreased aflatoxin B(1) levels in comparison with the control were observed with FA at 1, 10, 20 and 25 mM with the strains RCM89, RCM108 and RCM38 at a(w) = 0.971, 0.955 and 0.999 respectively. The data show that CA and FA can be considered as effective fungitoxicants for A. flavus and A. parasiticus in in vitro assay. The information obtained is part of an ongoing study to determine their application at the storage level.     

Germination induces accumulation of specific proteins and antifungal activities in corn kernels

ABSTRACT This study examined protein induction and accumulation during imbibition and germination of corn kernels, as well as antifungal activities of extracts from germinating kernels against Aspergillus flavus and Fusarium moniliforme. Genotypes studied included GT-MAS:gk and Mp420, which are resistant to A. flavus infection and aflatoxin accumulation, and Pioneer 3154 and Deltapine G-4666, which are susceptible to A. flavus infection and aflatoxin accumulation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis resolved five protein bands that were present at higher concentrations in germinated kernels than in nongerminated kernels. Western blot analyses revealed that one of these proteins reacted with the 22-kDa zeamatin antiserum, and a zeamatin-like protein accumulated to a higher concentration in germinated kernels. Two protein bands from dry kernels that reacted with ribosome-inactivating protein (RIP) antiserum were identified as the 32-kDa proRIP-like form and an 18-kDa peptide of the two peptides that form active RIP. However, in germinated kernels, two protein bands that reacted with RIP antiserum were identified as two RIP-like peptides with a molecular mass of approximately 18 and 9 kDa. Purified RIP and zeamatin from corn inhibited growth of A. flavus. Bioassays of germinated kernel extracts from all four genotypes exhibited antifungal activity against A. flavus and F. moniliforme, with extracts from the susceptible genotypes showing greater inhibition zones. This study provides evidence of protein induction in corn kernels during imbibition or the early stages of germination, and the induced proteins may be related to our previous findings of germination-associated resistance in the corn kernel, especially in the susceptible kernels.