Fusarium Thapsinum Research Articles

Response of near‐isogenic sorghum lines, differing at the P locus for plant colour, to grain mould and head smut fungi

AbstractLeaves and stalks of many sorghum genotypes accumulate dark red or purple pigments upon wounding while some plants, called ‘tan,’ do not. Grains with unpigmented ‘white’ pericarps grown on tan plants are more desirable for food. The hypothesis tested was that pigments in plants protected grain against the panicle diseases grain mould and head smut. Near‐isogenic tan or purple plant colour genotypes with white grain were planted at Lincoln and Ithaca, NE and Corpus Christi, TX. The field grown grain was plated onto semi‐selective media to detect the presence of grain colonisation by mould genera Alternaria, Fusarium and Curvularia. More Fusarium and Curvularia spp. were recovered from grain grown at Corpus Christi than the Nebraska locations; however, there was no indication that the grain from purple plants was more resistant to the three fungal genera. Most fungi were identified morphologically as Alternaria alternata. Molecular identification of Fusarium species, using translation elongation factor 1‐α gene sequences, showed that Fusarium thapsinum and Fusarium proliferatum infected grain at all three locations. Head smut disease of panicles, caused by the fungus Sporisorium reilianum, was assessed at Corpus Christi; surprisingly, purple plants had significantly greater disease incidence than tan plants. We propose that the tan plant colour lines with white grain are promising for development of food‐grade sorghums not more susceptible than pigmented lines to grain mould and head smut.

Morphological and Molecular Characterization of Fusarium Isolated From Maize in Syria

AbstractMaize is the third most important cereal after wheat and barley in Syria. Maize plants are attacked by several Fusarium species causing mainly stalk and ear rot of maize which poses a major impact worldwide. Identification of Fusarium species is important for disease control and for assessment of exposure risk to mycotoxines. To identify Fusarium species attacking maize in Syria, a total of 32 Fusarium isolates were recovered from maize ears collected from four different geographical regions, mainly from Ghouta surrounding Damascus. Fusarium isolates were identified based on morphology and on partial DNA sequencing of the TEF1‐α and rDNA/ITS genes. The majority (26 of 32) of these isolates was identified as F. verticillioides (subdivided into four groups), whereas three isolates turned out to be F. thapsinum, F. equiseti and F. andiyazi. The remaining three isolates were close to F. andiyazi, although further investigation is needed to confirm whether they represent a yet undescribed species. Furthermore, our results showed that sequencing the TEF1‐α gene is much more informative than sequencing of the rDNA/ITS region for Fusarium identification at the species level. PCR analysis showed that only F. verticillioides isolates were potentially fumonisin producers and that only the F. equiseti isolate was potentially trichotecene producer. This is the first report on Fusarium thapsinum, F. equiseti and F. andiyazi attacking maize in Syria.

Characterization of fluorescent Pseudomonas spp. associated with roots and soil of two sorghum genotypes

Sorghum is used as bioenergy feedstock, an- imal feed, and food. Economical methods for disease prevention and control are valuable for producers. Fluorescent Pseudomonas spp. were isolated from sor- ghumrootsandsurroundingsoilwiththegoaloffinding isolates that significantly inhibited sorghum fungal pathogens. Fluorescent pseudomonads were collected from seedlings of sorghum cultivars RTx433 and Redlan and wheat cultivar Lewjain, grown in two soils. Lewjain is known to support growth of producers of the antibiotic, 2,4-diacetylphloroglucinol (2,4-DAPG). Isolatesfrom all three plantswere assessedfor hydrogen cyanide (HCN) and extracellular protease production, and for a 2,4-DAPG gene, phlD .B oth soil type and plant type affected HCN- and protease-production, but phlD was not affected. Subsets of phlD + isolates were chosen to determine phlD genotypes and to conduct in vitro inhibitionassaysagainst sorghumpathogens.Most isolates from sorghum and wheat were genotype D, previously associated with superior root colonization. phlD + sorghum isolates were co-cultured with five sor- ghum pathogens. One isolate from each sorghum line exhibited inhibition to all five pathogens but more Redlan isolates were inhibitory to the virulent pathogen, Fusarium thapsinum, than RTx433 isolates. Nearly all inhibitory isolates from either sorghum cultivar were from one soil type. This is consistent with what had been previously observed in field studies: that soil type played a significant role in determining characteristics of fluo- rescent Pseudomonas spp. isolated from roots or soil, but sorghum genotype also had a considerable effect.

Isolation and characterization of the grain mold fungiCochliobolusandAlternariaspp. from sorghum using semiselective media and DNA sequence analyses

Mold diseases, caused by fungal complexes including Alternaria, Cochliobolus, and Fusarium species, limit sorghum grain production. Media were tested by plating Fusarium thapsinum, Alternaria sp., and Curvularia lunata, individually and competitively. Dichloran chloramphenicol rose bengal (DRBC) and modified V8 juice (ModV8) agars, found to be useful, were compared with commonly used agar media, dichloran chloramphenicol peptone (DCPA) and pentachloronitrobenzene (PCNB). Radial growth, starting with mycelia or single-conidia and hyphal tips, demonstrated an effect of media. For isolation of grain fungi, DRBC and ModV8 were similar or superior to DCPA and PCNB. When seedlings were inoculated with conidia of C. lunata, Alternaria sp., F. thapsinum, or mixtures, the percentage of root infection ranged from 28% to 77%. For mixed inoculations, shoot weights, lesion lengths, and percentage of root infections were similar to F. thapsinum inoculations; most colonies recovered from roots were F. thapsinum. For Alternaria grain isolates, 5 morphological types, including Alternaria alternata, were distinguished by colony morphologies and conidial dimensions. Sequence analysis using a portion of the endo-polygalacturonase gene was able to further distinguish isolates. Cochliobolus isolates were identified morphologically as C. lunata, Curvularia sorghina, and Bipolaris sorghicola. Multiple molecular genotypes were apparent from rRNA internal transcribed spacer region sequences from Cochliobolus grain isolates.

Characterization and pathogenicity of fungi and oomycetes associated with root diseases of date palms in Oman

Date palm is the most important crop in Oman and the Arabian Peninsula. A study was conducted to investigate fungal and oomycete pathogens associated with root diseases of date palms in Oman. Isolations were done from date palm roots showing root rot/necrosis symptoms. The root samples were collected from 111 date palm trees representing 29 different date palm cultivars. Morphological and molecular identification of the isolated fungi and oomycetes showed that they belong to 34 different fungal and oomycete species. Fusarium solani (27%), Ceratocystis radicicola (25%) and Lasiodiplodia theobromae (19%) were found to be the most common pathogens associated with root diseases of date palms. Pathogenicity tests on seedlings of date palm cv. Khalas showed that 21 fungal and oomycete species are pathogenic on date palm seedlings. The pathogenic species produced root rot, root necrosis or wilt symptoms upon inoculation on date palm seedlings. A total of 1, 7, 13 and 10 fungal and oomycete pathogens were found to be aggressive, moderately aggressive, weak and non-pathogenic on date palm seedlings, respectively, with C. radicicola being the most aggressive. Among the 21 pathogenic species, 13 are reported in this study for the first time as new root pathogens of date palm on a global basis. These include Ceratocystis omanensis, Cochliobolus hawaiiensis, Exserohilum rostratum, Corynascus kuwaitiensis, Fusarium brachygibbosum, Fusarium acuminatum, Fusarium redolens, Fusarium thapsinum, Nigrospora sphaerica, Phoma multirostrata, Pythium indigoferae, Pythium spinosum and Pythium ultimum var. ultimum. In addition, this study reports for the first time the occurrence of 22 fungal and oomycete species in Oman.

Presence of Fusarium spp. in Air and Soil Associated with Sorghum Fields.

Sorghum grain, valuable for feed, food, and bioenergy, can be colonized by several Fusarium spp.; therefore, it was of interest to identify possible sources of conidia. Analysis of air and soil samples provided evidence for the presence of propagules from Fusarium genotypes that may cause grain infections. Soil population estimates of members of the Gibberella fujikuroi species complex, that includes sorghum pathogens and other Fusarium spp., suggested that adequate inoculum for systemic infections was present. Conidia in air samples within two sorghum fields were collected by passive trapping for 2 years. Subsampled Fusarium isolates indicated that numbers of G. fujikuroi increased from anthesis through maturity, which coincides with grain development stages vulnerable to Fusarium spp. Genotyping using translation elongation factor 1-α gene sequences revealed that spore trap isolates included members of G. fujikuroi that are sorghum pathogens: Fusarium thapsinum, F. verticillioides, F. proliferatum, and F. andiyazi. Also detected were F. graminearum, F. subglutinans, and several F. incarnatum-F. equiseti species complex haplotypes that colonize sorghum asymptomatically. All commonly found grain colonizers were detected from air samples in this study.

Evaluation of the Ugandan sorghum accessions for grain mold and anthracnose resistance

Sorghum accessions from Uganda were evaluated for grain mold and anthracnose resistance during the 2005 and 2006 growing seasons at the Texas A&M University Research Farm, near College Station, TX. Accession PI534117 and SC719-11E exhibited the lowest grain mold severities of 2.4, whereas, accessions PI534117, PI534144, PI576337, PI297199, PI533833, and PI297210, with SC748-5 were highly resistant to anthracnose in both years. Accessions PI534117, PI297134, PI297156 exhibited low grain mold severities in 2006. Significant negative correlation was recorded between grain mold and percent germination and high temperature in both years. In 2006, daily precipitation recorded significant positive correlation with grain mold. The seed mycoflora was analyzed across sorghum lines and treatments. In 2005, Curvularia lunata and Fusarium thapsinum were the most frequently recovered fungal species with 31 and 21% incidence, respectively, followed by Alternaria spp. (19%) and F. semitectum (13%). In 2006, predominant colonizers were F. thapsinum (58%), followed by Alternaria and F. semitectum with 15 and 10, percent respectively, while C. lunata had a 6% incidence. In this study, PI534117 holds promise for multiple disease resistance, as it had the lowest disease severity of grain mold and was highly resistant to anthracnose in both years. It also has a high germination rate, a high seed weight, and its short stature is more advantageous for the new A-line conversion program.

Tetrazolium violet staining of naturally and artificially moulded sorghum (Sorghum bicolor (L.) Moench) caryopses

Sorghum grain mould (GM) is a yield-limiting disease characterized by damage to caryopsis embryo tissues. Caryopses were obtained from naturally weathered (n.w.) panicles and panicles inoculated with Fusarium thapsinum (FT) and Curvularia lunata (CL) at anthesis. Caryopses were assayed for tetrazolium violet (TZ) viability, embryo damage, germination, and pathogen isolation. In n.w. and artificially inoculated (a.i.) caryopses, Tx430 (GM-susceptible) showed low whole embryo TZ viability, whereas Sureno and Tx2911 (GMresistant) showed higher values. Tx430 had the greatest levels of non-staining scutellum, coleoptile, plumule, radicle tissues, non-staining tissues and damaged embryos under both inoculation regimes. In n.w. grain, TZ staining overestimated germination for some genotypes (especially Tx430), whereas TZ staining underestimated germination in most a.i. material. Correlations between TZ viability and germination were positive and significant for n.w. and a.i. caryopses. FT and F. proliferatum (FP) were the most commonly isolated fungi from n.w. grain. Correlations between yellow-pigmented-FT, FP, and CL incidence from sorghum caryopses and TZ viability were negative and significant. This study showed that TZ viability differs in a genotype- and pathogendependent manner. Therefore, this approach will have utility in screening sorghum germplasm for grain mould resistance at the whole embryo and tissue level.

Identification and Characterization of Toxigenic Fusaria Associated with Sorghum Grain Mold Complex in India

Fusarium species are dominant within the sorghum grain mold complex. Some species of Fusarium involved in grain mold complex produce mycotoxins, such as fumonisins. An attempt was made to identify Fusarium spp. associated with grain mold complex in major sorghum-growing areas in India through AFLP-based grouping of the isolates and to further confirm the species by sequencing part of α-Elongation factor gene and comparing the sequences with that available in the NCBI database. The dendrogram generated from the AFLP data clustered the isolates into 5 groups. Five species of Fusarium--F. proliferatum, F. thapsinum, F. equiseti, F. andiyazi and F. sacchari were identified based on sequence similarity of α-Elongation factor gene of the test isolates with those in the NCBI database. Fusarium thapsinum was identified as predominant species in Fusarium--grain mold complex in India and F. proliferatum as highly toxigenic for fumonisins production. Analysis of molecular variance (AMOVA) revealed 54% of the variation in the AFLP patterns of 63 isolates was due to the differences between Fusarium species, and 46% was due to differences between the strains within a species.

Alteration in Lignin Biosynthesis Restricts Growth of Fusarium spp. in Brown Midrib Sorghum

To improve sorghum for bioenergy and forage uses, brown midrib (bmr)6 and -12 near-isogenic genotypes were developed in different sorghum backgrounds. The bmr6 and bmr12 grain had significantly reduced colonization by members of the Gibberella fujikuroi species complex compared with the wild type, as detected on two semiselective media. Fusarium spp. were identified using sequence analysis of a portion of the translation elongation factor (TEF) 1-alpha gene. The pathogens Fusarium thapsinum, F. proliferatum, and F. verticillioides, G. fujikuroi members, were commonly recovered. Other frequently isolated Fusarium spp. likely colonize sorghum asymptomatically. The chi(2) analyses showed that the ratios of Fusarium spp. colonizing bmr12 grain were significantly different from the wild type, indicating that bmr12 affects colonization by Fusarium spp. One F. incarnatum-F. equiseti species complex (FIESC) genotype, commonly isolated from wild-type and bmr6 grain, was not detected in bmr12 grain. Phylogenetic analysis suggested that this FIESC genotype represents a previously unreported TEF haplotype. When peduncles of wild-type and near-isogenic bmr plants were inoculated with F. thapsinum, F. verticillioides, or Alternaria alternata, the resulting mean lesion lengths were significantly reduced relative to the wild type in one or both bmr mutants. This indicates that impairing lignin biosynthesis results in reduced colonization by Fusarium spp. and A. alternata.

Expression of pathogenesis‐related protein PR‐10 in sorghum floral tissues in response to inoculation with Fusarium thapsinum and Curvularia lunata

Differences in grain mould disease levels among different sorghum varieties grown in the same environment imply that host genes play a role in controlling disease severity. The fungi most often recovered from naturally infected sorghum grain, Fusarium thapsinum and Curvularia lunata, were used to inoculate a set of resistant and susceptible cultivars at anthesis in both field and glasshouse trials. In the field, 12 cultivars were inoculated with a mixture of F. thapsinum and C. lunata and, in the glasshouse, individual panicles from four selected cultivars were inoculated with spore suspensions of C. lunata, F. thapsinum, a mixture of the two or water to serve as a control. Based on grain mould severity ratings and germination tests on the seed from the field trial, Tx2911, Sureno, SC719-11E and SC650-11E displayed a high level of resistance to grain mould. To determine whether resistant and susceptible lines differed in response to the pathogens, PR-10 mRNA levels were measured using real-time reverse transcriptase-polymerase chain reaction. PR-10 is a protein with antifungal properties that has been associated with defence responses in sorghum and other plant species. In field tests, most, but not all, cultivars showed significant induction of normalized relative quantities of PR-10 after dual inoculation with spores of both C. lunata and F. thapsinum. Under glasshouse-controlled conditions, glumes of inoculated plants showed the clear induction of PR-10 mRNA, and the response was greater in resistant (Tx2911 and Sureno) than in susceptible (RTx430 and SC170-6-17) cultivars. Inoculation with spores from a single mould-inducing pathogen generally induced greater responses than when spores were combined. For RTx430, SC170-6-17 and Sureno, the response to C. lunata was greater, whereas Tx2911 showed a stronger response to F. thapsinum. The results indicate that the induction of PR-10 in sorghum glumes may be a factor useful in breeding programmes designed to combine multiple factors for resistance.

A molecular based strategy for rapid diagnosis of toxigenic Fusarium species associated to cereal grains from Argentina

Fusarium species are worldwide causal agents of ear rot in cereals. Their toxigenic potential is a health risk for both humans and animals. In Argentina, most identification of these fungi has been based on morphological and cross-fertility criteria which are time consuming and require considerable expertise in Fusarium taxonomy and physiology. DNA based approaches have been reported as rapid, sensitive and specific alternatives to identify the main fumonisin and trichothecene-producing Fusarium species. In this work, we used PCR assays and the partial sequence of TEF1-α gene (Translation Elongation Factor-1α) to identify the fumonisin and trichothecene-producing species in Fusarium isolates from diverse regions of Argentina. The relative efficiency and reliability of those methods to improve mycotoxin risk prediction in this country were also assessed. Species-specific PCR assays were targeted toward multicopy IGS (Intergenic Spacer of rDNA units) and on the toxin biosynthetic genes FUM1 (fumonisins) and TRI13 and TRI7 genes (trichothecenes). PCR assays based on FUM1 gene and IGS sequences allowed detection and discrimination of the fumonisin producers Fusarium proliferatum and Fusarium verticillioides. Molecular identification of nonfumonisin producers from Gibberella fujikuroi species complex was possible after determination of TEF1-α gene sequences, which indicated the presence of Fusarium subglutinans, Fusarium andiyazi and Fusarium thapsinum. TEF-1α gene sequences also allowed discrimination of the different species of the Fusarium graminearum complex ( F. graminearum sensu lato) as F. graminearum sensu stricto, Fusarium meridionale and Fusarium boothii. The last two species belonged to NIV chemotype and were detected for the first time in the subtropical region of Argentina while F. graminearum sensu stricto was DON producer only, which was also confirmed by specific PCR assays based on TRI137/ TRI7 genes. Our results indicated that the PCR assays evaluated in this work are reliable diagnostic tools to detect the main toxigenic Fusarium species associated to cereal grains in Argentina. An extensive epidemiological survey based on the approach presented in this work is currently in progress to know the mycotoxigenic hazard of Fusarium species in cereal grains from the subtropical region of Argentina.

The Grain Mold Pathogen, Fusarium thapsinum, Reduces Caryopsis Formation in Sorghum bicolor

AbstractGrain mold is a globally important panicle disease of sorghum [Sorghum bicolor (L.) Moench] that occurs between floral anthesis and physiological maturity of the caryopsis. Many fungi, including Fusarium thapsinum, cause grain mold. In this study, sorghum florets of grain mold resistant (Sureno and Tx2911), moderately resistant (SC170), and susceptible (Tx430) cultivars were spray‐inoculated with a high density (1 × 106 microconidia/ml) of F. thapsinum at anthesis. Mean caryopsis formation frequencies [CFF = (total caryopses/total spikelets per panicle) × 100] for F. thapsinum‐inoculated Sureno and Tx2911 panicles did not significantly differ from their respective controls, however F. thapsinum‐inoculated SC170 and Tx430 panicles were significantly less than controls. In addition, CFF was significantly reduced in F. thapsinum‐inoculated Tx430 panicles when compared to the F. thapsinum‐inoculated grain mold resistant genotypes (P = 0.011). This study suggests that screening of sorghum varieties for caryopsis formation using high‐density inoculations at anthesis would provide an additional assay to measure F. thapsinum resistance in the greenhouse.

Inoculation strategies to assess biological interactions between Fusarium and Alternaria species infecting sorghum

New cultivars of sorghum are being developed for increased food use, as livestock feed, and for the bioenergy industry by manipulation of secondary metabolic pathways through breeding. Previous work has suggested that such modifications may have an impact on cultivar response to fungal pathogens. We investigated four inoculation strategies that may be used in studies involving pathogens of sorghum. Plants of elite sorghum genotypes ‘Wheatland’ and RTx430, commonly used in breeding programs, were inoculated with isolates of Alternaria alternata, Fusarium equiseti, Fusarium proliferatum, Fusarium solani, Fusarium thapsinum, and Fusarium verticillioides recovered from field-grown sorghum. Wound inoculation of the peduncles of heads at anthesis demonstrated that isolates of F. verticillioides and F. thapsinum produced mean lesion lengths that were significantly greater than control inoculations. The length of this assay was decreased by inoculating fungi onto plants of a very early maturing sorghum line (N247). Spraying heads at anthesis with conidial suspensions over three consecutive days in the greenhouse was conducted to attempt to mimic conditions in the field. Results indicated that plants treated with conidia of F. thapsinum may develop mature grain with reduced germination. Seed and seedling inoculations produced responses over a relatively short time period. Seed inoculations were conducted in a manner similar to a corn bioassay. Seedling inoculations, conducted in Magenta vessels, allowed for measurement of effects of inoculum on roots, stalks, and leaves. Following inoculation of RTx430 and ‘Wheatland’ plants grown in Magenta vessels with F. thapsinum, nearly all measurements were significantly different from those of the water controls except for percent root infection of RTx430. Key words: sorghum pathogens, Alternaria alternata, Fusarium equiseti, Fusarium solani, Fusarium thapsinum, Fusarium verticillioides, Sorghum bicolor, inoculation methods. De nouveaux cultivars de sorgho plus productifs sont à l’heure actuelle développés par manipulation des voies métaboliques secondaires durant le processus de sélection. Ces nouveaux cultivars sont destinés à l’alimentation des humains, à celle du bétail ainsi qu’à l’industrie des bioénergies. Des travaux précédents ont suggéré que de telles modifications peuvent influencer la réponse des cultivars quant à leur résistance aux agents pathogènes fongiques. Nous avons étudié quatre stratégies d’inoculation qui peuvent être utilisées dans les études relatives aux agents pathogènes qui s’attaquent au sorgho. Des plants de génotypes élites de sorgho ‘Wheatland’ et RTx430, communément utilisés dans les programmes de sélection, ont été inoculés avec des isolats d’ Alternaria alternata, de Fusarium equiseti, de Fusarium proliferatum, de Fusarium solani, de Fusarium thapsinum et de Fusarium verticillioides obtenus de plants de sorgho cultivés en champs. L’inoculation de blessures causées aux pédoncules des épis arrivés au stade de l’anthèse a démontré que les isolats de F. verticillioides et de F. thapsinum produisaient des lésions dont les longueurs moyennes étaient passablement plus grandes que celles produites par les inoculations témoins. La durée de ce biotest a été raccourcie en inoculant des plants d’une lignée très hâtive de sorgho (N247) avec des champignons. Afin d’essayer de reproduire les conditions de plein champ, les épis, au stade de l’anthèse, ont été vaporisés, en serre, avec une suspension conidiale, et ce, sur une période de trois jours consécutifs. Les résultats ont montré que les plants traités avec les conidies de F. thapsinum peuvent produire des grains matures, mais que leur taux de germination sera réduit. Les inoculations de graines et de plantules induisent des réponses à brève échéance. Les inoculations de graines furent effectuées selon une méthode semblable à celle utilisée pour les biotests effectués sur le maïs. Les inoculations des plantules, faites dans des boîtes Magenta, ont permis de mesurer les effets de l’inoculum sur les racines, les tiges et les feuilles. À la suite de l’inoculation avec F. thapsinum des plants de RTx430 et de ‘Wheatland’ cultivés dans les boîtes Magenta, presque toutes les mesures effectuées variaient passablement de celles provenant des solutions témoins aqueuses, sauf pour ce qui est du taux d’infection des racines de RTx430. Mots-clés : agents pathogènes du sorgho, Alternaria alternata, Fusarium equiseti, Fusarium solani, Fusarium thapsinum, Fusarium verticillioides, Sorghum bicolor, méthodes d’inoculation.

In Vitro Antifungal Susceptibility and Molecular Characterization of Clinical Isolates of Fusarium verticillioides ( F. moniliforme ) and Fusarium thapsinum

A microdilution method was used to test 11 antifungal drugs against clinical isolates of Fusarium thapsinum and three different phylogenetic clades of Fusarium verticillioides that were characterized by sequencing a region of the beta-tubulin gene. Terbinafine was the most-active drug against both species, followed by posaconazole against F. verticillioides.

Characterization and genetic variability ofFusarium verticillioidesstrains isolated from corn and sorghum in Brazil based on fumonisins production, microsatellites, mating type locus, and mating crosses

Fusarium verticillioides (Gibberella fujikuroi mating population A) is a producer of fumonisins and one of the main contaminants of corn grains. In Brazil, some studies analyzing strains isolated from corn have demonstrated high levels of fumonisins, whereas the levels for strains isolated from sorghum have been found to be low. In the present study, we investigated the genetic diversity of 22 F. verticillioides strains isolated from corn and 21 strains isolated from sorghum cultivated in the State of São Paulo, Brazil. Differences in the genetic profile were observed between the strains isolated from the two substrates using single primer amplification reaction by polymerase chain reaction (SPAR-PCR). Fumonisins levels were higher in strains isolated from corn than in those isolated from sorghum. The MAT-1 and MAT-2 alleles were identified by PCR, and the isolates were subsequently crossed with Fusarium thapsinum (G. fujikuroi mating population F) reference strains because this species is morphologically similar to F. verticillioides and produces low levels of fumonisins. The SPAR haplotypes of some strains isolated from sorghum were similar to the F. thapsinum reference strain haplotypes, but there was no fertile mating between the strains isolated from the two substrates and the F. thapsinum references strains. The MAT-1:MAT-2 proportion was 5:17 and 14:7 for isolates from corn and sorghum, respectively.

Analysis of chitinase isoenzymes in sorghum seedlings inoculated with Fusarium thapsinum or F. proliferatum

An investigation was conducted on the chitinase isoenzymes in various tissues of 1-week-old sorghum seedlings that had been inoculated with the fungal pathogens Fusarium thapsinum and Fusarium proliferatum. Electrophoresis of non-denatured extracts on SDS-PAGE gels revealed at least 11 bands of activity. Using native PAGE gels, seven acidic isoenzymes and four basic isoenzymes were identified. Two acidic chitinases were expressed constitutively and their activity did not differ between control and inoculated seedlings. The activity of the other acidic isoenzymes increased in all tissues following inoculation. The activities of both inducible and constitutive acidic chitinase isoenzymes were higher in the scutellum than in other tissues. Inducible basic chitinases increased only in the roots and shoots after infection, while the activity of basic chitinases decreased in the seed and scutellum. The pattern of chitinase isoenzymes from dormant caryopses was different from that in seed-derived tissues in the seedling. Generally, seedling tissues infected with Fusarium fungi had higher levels of acidic isoenzymes and lower levels of basic isoenzymes than dormant caryopses. The findings were consistent with hypotheses that acidic chitinases are primarily involved in active defence responses, while basic chitinases are part of pre-formed defence mechanisms.

Induction of Defence Responses in Roots and Mesocotyls of Sorghum Seedlings by Inoculation with Fusarium thapsinum and F. proliferatum, Wounding and Light

AbstractThe defence reactions of sorghum seedlings 7 days after inoculation with Fusarium thapsinum and F. proliferatum, and interactions with wounding and exposure to light were studied to determine whether responses to these fungi differed from those to abiotic stresses. In non‐wounded plants, inoculation with both fungi increased concentrations of anthocyanins and soluble phenolics and activities of peroxidase (POX), chitinase and β‐1,3‐glucanase in the roots, and increased β‐1,3‐glucanase activity in the mesocotyls. There was no effect of inoculation on phenylalanine ammonia‐lyase (PAL) activity. Wounding by itself increased anthocyanin content of mesocotyls. Wounding also had a variety of interactions with inoculation. Exposure to light had very little effect on any defence response measured. A time course experiment showed that induction of chitinase and β‐1,3‐glucanase occurred in less than 24 h after inoculation. POX activity increased 2 days after inoculation, followed by a transient increase in PAL activity. The content of anthocyanins and soluble phenolics in roots of inoculated seedlings increased gradually compared with controls over 6 days. The responses of sorghum seedlings to inoculation with F. thapsinum and F. proliferatum were similar to those found by other workers following challenge by necrotrophic pathogens and were different from those induced by wounding and exposure to light.

Role of Chitinase and Sormatin Accumulation in the Resistance of Sorghum Cultivars to Grain Mold

Experiments were conducted to determine the association between resistance to grain mold and the accumulations of chitinase and sormatin. Eight sorghum lines were treated at 50% bloom with Fusarium thapsinum, Curvularia lunata, a mixture of the two fungi, and a water-sprayed control. At maturity, percent disease severity, seed germination rates, and kernel weight were recorded. Chitinase and sormatin content (mg/g of dry weight) were measured in seed samples taken at 30 and 50 days after treatment (DAT). Seed chitinase content was moderately affected by sorghum line (P = 0.10) and significantly affected by the developmental stage of the kernels (P = 0.05). Cultivars Sureno, 98LB650, and 98LB723 exhibited larger negative changes in chitinase content at 50 DAT over water-sprayed control treatment at 30 DAT than the susceptible cultivars Dorado, RTx2536, and RTx430. In 2000, significant negative correlations were observed for percent disease severity and chitinase content at 30 DAT, seed germination and sormatin content at 50 DAT, and between seed germination and kernel weight. There also was a significant positive correlation between germination and chitinase content at 30 DAT. No association between disease severity and changes in chitinase content at 50 DAT was observed. Sormatin content also was significantly affected by the stage of kernel development. Sorghum cultivars inoculated with fungal pathogens responded differently as indicated by the significant sorghum line x treatment interaction for sormatin content in 2000. In both years, larger increases in sormatin content over the water-sprayed control treatments were observed on moderately susceptible to susceptible cultivars such as 98LB650, 98LB723, 98LB789, RTx430, and RTx2536 than on Sureno. Except for percent disease severity and germination, there was no significant association among all of the other parameters measured in 2001. The results of this study did not clearly demonstrate a strong association between resistance to grain mold and the accumulation of sormatin and chitinase. Thus, there is the possibility that certain moderately resistant to resistant sorghum cultivars, such as Sureno, may employ other strategies to eschew or restrict fungal invasion either before or after physiological maturity.

Species diversity of and toxin production by Gibberella fujikuroi species complex strains isolated from native prairie grasses in Kansas.

Fusarium species from agricultural crops have been well studied with respect to toxin production and genetic diversity, while similar studies of communities from nonagricultural plants are much more limited. We examined 72 Fusarium isolates from a native North American tallgrass prairie and found that Gibberella intermedia (Fusarium proliferatum), Gibberella moniliformis (Fusarium verticillioides), and Gibberella konza (Fusarium konzum) dominated. Gibberella thapsina (Fusarium thapsinum) and Gibberella subglutinans (Fusarium subglutinans) also were recovered, as were seven isolates that could not be assigned to any previously described species on the basis of either morphological or molecular characters. In general, isolates from the prairie grasses produced the same toxins in quantities similar to those produced by isolates of the same species recovered from agricultural hosts. The G. konza isolates produce little or no fumonisins (up to 120 micro g/g by one strain), and variable but generally low to moderate amounts of beauvericin (4 to 320 micro g/g) and fusaproliferin (50 to 540 micro g/g). Toxicity to Artemia salina larvae within most species was correlated with the concentration of either beauvericin or fusaproliferin produced. Organic isolates from some cultures of G. moniliformis were highly toxic towards A. salina even though they produced little, if any, beauvericin or fusaproliferin. Thus, additional potentially toxigenic compounds may be synthesized by G. moniliformis strains isolated from prairie grasses. The Fusarium community from these grasses appears to contain some species not found in surrounding agricultural communities, including some that probably are undescribed, and could be capable of serving as a reservoir for strains of potential agricultural importance.