Field performance of maize grown from <Emphasis Type="Italic">Fusarium verticillioides</Emphasis>-inoculated seed

Fusarium verticillioides is an important fungus occupying dual roles in the maize plant. The fungus functions as an endophyte, a fungal/host interaction beneficial to the growth of some plants. At other times, the fungus may function as a mycotoxin producing pathogen. The advantages and/or disadvantages of the endophytic relationship must be established in order to target appropriate sites for controlling diseases and mycotoxins in maize. One possibility could be to ensure seed maize is fungal free prior to planting. Reciprocal inoculations were made with two fungal isolates on seed of two maize genotypes. Yield was measured at harvest by ear and seed characters and vegetative growth at one-month intervals for plant survival, height, weight and stem diameter. Yield and vegetative growth differed among mature plants only once based on seed inoculation status. In 1998, plant weight was reduced and seed weight per ear was increased for the dent maize, GT-MAS: gk, grown from F. verticillioides RRC 374- inoculated seed compared to other seed treatments. Most vegetative characters were reduced at the first collection for Silver Queen plants grown from F. verticillioides-inoculated seed in 1997 and 1999, but not in 1998. However, no significant differences occurred among mature Silver Queen plants during any of the three growing seasons. In conclusion, yield and vegetative growth of mature maize plants grown from F. verticillioides-inoculated seed were equal to or greater than plants grown from non-inoculated seed under south Georgia field conditions during 1997, 1998, and 1999.     

Chilling and photosynthetic productivity of field grown maize (Zea mays); changes in the parameters of the light-response curve,canopy leaf CO2 assimilation rate and crop radiation-use efficiency

The effect of growth temperatures on the photosynthetic performance of field grown maize (Zea mays cv. LG11) was examined for crops sown on 1 May and 28 June 1991. During the period of growth, 2 May to 10 August, the early-sown crop experienced temperatures below 10 °C on 33 occasions compared with only one for the crop sown on 28 June. The prolonged period of low temperatures throughout May and beginning of June were associated with a marked depression in CO₂ assimilation rates at all light levels in the early-sown treatment. Chill-induced depression of the photosynthetic light-response curve reflected a sustained reduction in canopy leaf photosynthesis and crop radiation-use efficiency (RUE). During the early stages of growth, RUE was 65% lower in the early- than late-sown treatment, with no marked recovery observed in the former treatment until approximately three weeks after chilling conditions had ceased. Data show a close correlation between chill-induced depression of quantum yield () and RUE, with corresponding reductions in the light-saturated rates of CO₂ assimilation (P_max). The convexity of the light-response curve recovered most rapidly from chilling temperatures, and at least three weeks before any improvement in RUE. It is concluded that photosynthetic productivity of immature maize stands is less sensitive to changes in the convexity of the light response, than to changes in either or P_max.     

Effects of long-term NP-fertilization on abundance and diversity of arbuscular mycorrhizal fungi under a maize cropping system

Diversity of arbuscular mycorrhizal fungi (AMF) in 27-year long-term NP-fertilization plots under a maize cropping system in Thailand was studied through spore morphological characterization. The plots received 0–0, 60–60, 120–120 and 180–180 kg N-P₂O₅ ha^–1 year^–1 as ammonium sulfate and triple superphosphate. The plots were sampled monthly for one year, the AMF spores were counted and morphotyped, and taxa were identified after morphotyping and monospecific pot culture. Spore number g^–1 soil, relative spore abundance and Shannon-Wiener indexes were calculated. Sixteen putative taxa were recorded from the field of which nine sporulated on maize roots in pot culture. The long-term fertilization caused decreases in AMF total spore numbers and variation in species diversity depended on sampling time. Effects of fertilization on spore number and also relative spore abundance varied with species and sampling time. Among the nine species sporulating under maize, only Acaulospora sp.1 showed no change (P > 0.003 after Bonferroni correction) in spore number with fertilization in the field; and was therefore classified as an AMF species insensitive to fertilization. Spores of Entrophospora schenckii, Glomus mosseae, Glomus sp.1, Glomus geosporum-like and Scutellospora fulgida, though they decreased in absolute numbers in response to fertilization, showed no change (P > 0.003 after Bonferroni correction) in relative abundance; these species were classified as AMF species slightly sensitive to fertilization. Three unidentified species of Glomus, though they decreased in absolute numbers in response to fertilization, showed decreases (P < 0.003 after Bonferroni correction) in relative abundance; these species were classified as AMF species highly sensitive to fertilization.     

Changes in the photosynthetic light response curve during leaf development of field grown maize with implications for modelling canopy photosynthesis

Changes in the photosynthetic light-response curve during leaf development were determined for the fourth leaf of maize crops sown on 23 April and 10 June. Temperatures were unusually mild during late spring/early summer and neither crop experienced chilling damage. The concept of thermal time was used to take into account the effects of different temperature regimes on developmental stage, thereby enabling photosynthetic light-response data to be combined for both crops to describe the general response. Large variations in the upper asymptote (A_sat) and convexity () of the light-response curve occurred during leaf development, but the maximum quantum yield of CO₂ assimilation remained relatively constant throughout. Dark respiration rates showed a small but significant decrease with leaf age and generally ranged between 5 and 10% of A_sat. A simple mathematical model was developed to assess the sensitivity of daily leaf photosynthesis (A_L) to reductions in the A_sat, and the initial slope () of the light-response curve at different stages of leaf development. On bright sunny days, and at all developmental stages, A_L was ca. twice as sensitive to reductions in A_sat than to reductions in and . In overcast conditions, however, all three parameters contributed significantly to reductions in leaf photosynthesis, although the contribution of was greatest during early leaf growth, while older leaves were most sensitive to depressions in A_sat. The implications of these results for modelling the sensitivity of canopy photosynthesis to chill-induced photoinhibition of the light-response curve are discussed.     

Potential bio-control agent for management of post-flowering stalk rot complex and maize plant health

The of aim of this study was to evaluate the potentiality of the native isolate of Trichoderma harzianum from IARI farm for the management of post-flowering stalk rot of maize and improvement of plant health. The treatment was tried as a seed treatment with the potent commercial formulation Kalisena SD (Aspergillus niger), neem kernel powder and effective fungicides (Thiram, Carbendazim, Captan) for comparison of its efficacy. The minimum disease was recorded in plots treated with native isolate both due to Fusarium moniliforme and Macrophomina phaseolina. The fungicides Carbendazim and Thiram ranked second in controlling the disease due to F. moniliforme and M. phaseolina, respectively. Plant health with respect to vigour and plant stand were found to be better than those of all the other treatments. It is concluded that the native isolate of T. harzianum may be used for maintaining good plant health and managing post-flowering stalk rot of maize.     

More than 400 million years of evolution and some plants still can't make it on their own: plant stress tolerance via fungal symbiosis

All plants in natural ecosystems are thought to be symbioticwith mycorrhizal and/or endophytic fungi. Collectively, thesefungi express different symbiotic lifestyles ranging from parasitismto mutualism. Analysis of Colletotrichum species indicates thatindividual isolates can express either parasitic or mutualisticlifestyles depending on the host genotype colonized. The endophytecolonization pattern and lifestyle expression indicate thatplants can be discerned as either disease, non-disease, or non-hosts.Fitness benefits conferred by fungi expressing mutualistic lifestylesinclude biotic and abiotic stress tolerance, growth enhancement,and increased reproductive success. Analysis of plant–endophyteassociations in high stress habitats revealed that at leastsome fungal endophytes confer habitat-specific stress toleranceto host plants. Without the habitat-adapted fungal endophytes,the plants are unable to survive in their native habitats. Moreover,the endophytes have a broad host range encompassing both monocotsand eudicots, and confer habitat-specific stress tolerance toboth plant groups. Key words: Colletotrichum, fungal endophytes, stress tolerance, symbiosis, symbiotic lifestyle Received 19 June 2007; Revised 25 November 2007 Accepted 30 November 2007     

Effects of host plant environment and Ustilago maydis infection on the fungal endophyte community of maize (Zea mays)

The focus of many fungal endophyte studies has been how plants benefit from endophyte infection. Few studies have investigated the role of the host plant as an environment in shaping endophyte community diversity and composition. The effects that different attributes of the host plant, that is, host genetic variation, host variation in resistance to the fungal pathogen Ustilago maydis and U. maydis infection, have on the fungal endophyte communities in maize (Zea mays) was examined. The internal transcribed spacer (ITS) region of the rDNA was sequenced to identify fungi and the endophyte communities were compared in six maize lines that varied in their resistance to U. maydis. It was found that host genetic variation, as determined by maize line, had significant effects on species richness, while the interactions between line and U. maydis infection and line and field plot had significant effects on endophyte community composition. However, the effects of maize line were not dependent on whether lines were resistant or susceptible to U. maydis. Almost 3000 clones obtained from 58 plants were sequenced to characterize the maize endophyte community. These results suggest that the endophyte community is shaped by complex interactions and factors, such as inoculum pool and microclimate, may be important.     

Pathogen incidence and their potential as microbial control agents in IPM of maize stem borers in West Africa

A review of the existing basis for maize stem borer IPM is given and the role of pathogens in the system is evaluated. Survey work outlining the major groups of insect pathogens is described; fungi (Beauveria bassiana and Metarhizium anisopliae), bacteria (Bacillus thuringiensis and Serratia marcesens), and viruses (granuloviruses and cytoplasmic polyhedroviruses) were identified. The presence of other unidentified protozoans, nematodes, fungi and viruses was noted. The virulence of some of the more promising known insect pathogens was explored in preliminary bioassays. Considering the cryptic habits of the insects, and the low input agriculture practiced by the majority of maize farmers in sub-Saharan Africa, Beauveria bassiana isolates possessing the capacity to grow systemically in the maize plant are considered one of the more interesting candidates for development as microbial control agents despite limited control in preliminary trials. Further work should also investigate the potential of pathogens of moderate virulence, such as the protozoans and CPVs.     

Leaf axil sampling of midwest U.S. maize for mycotoxigenic Fusarium fungi using PCR analysis

PCR analysis was used to detect Fusarium species generically, as well as the mycotoxin-producing species F.␣subglutinans, F. proliferatum, and F. verticillioides in leaf axil and other maize tissues during ear fill in a multiyear study in central Illinois. The frequency of Fusarium detected varied from site to site and year to year. Fusarium was generically detected more frequently in leaf axil material than in leaf/husk lesions. In two growing seasons, the leaf axil samples were also tested for the presence of the mycotoxin producing species F. proliferatum, F. subglutinans, and F. verticillioides. Overall, F. proliferatum and F. verticillioides were detected less often than F. subglutinans. Fusarium was generically and specifically detected most commonly where visible fungal growth was present in leaf axil material. Disclaimer: The mention of firm names or trade products in this article does not imply that they are endorsed or recommended by the United States Department of Agriculture over other firms or similar products not mentioned.     

Ecology of aflatoxin producing fungi and biocontrol of aflatoxin contamination

Summary  Aflatoxins, highly toxic and carcinogenic compounds that frequently contaminate foods and feeds, are produced by several genera in the genusAspergillus. Aspergillus flavus, the most common species causing crop contamination, is a common inhabitant of the Sonoran desert of North America where it resides in complex communities composed of diverse individuals. This diversity reflects divergent adaptation to various ecological niches. SomeA. flavus isolates that are well adapted to plant associated niches do not produce aflatoxins yet have the capacity to competitively exclude aflatoxin producers. These atoxigenic strains can serve as biological control agents for management of aflatoxins in crops. Detailed knowledge of the ecology of aflatoxin-producing fungi may lead to novel practical methods for limiting contamination. Presented at the EU-USA Bilateral Workshop on Toxigenic Fungi & Mycotoxins, New Orleans, USA, July 5–7, 2005.     

茄病镰刀菌感染致角膜溃疡1例

报告1例由茄病镰刀菌感染引起的角膜溃疡。患者男性,40岁,木工,左眼红、痛、流泪、视力下降10 d。经过角膜清创,系统性及局部抗真菌治疗后好转。致病菌株经真菌学鉴定为茄病镰刀菌,它是真菌性角膜炎的常见致病菌之一。真菌性角膜炎病程进展迅速,能否及早诊治关系预后。真菌学检查是确诊的依据,临床应予重视。     

Angiosperm DNA contamination by endophytic fungi: Detection and methods of avoidance

PCR primers with broad applicability are useful in many molecular-based studies; however, their universality can compromise results when DNA contaminants also are amplified. Eighty-one templates ofDahlia (Asteraceae), primarily extracted from native Mexican populations, were tested for the presence of fungal contaminants; out of these, almost 1 in 7 templates (13.6%) was contaminated. In a second survey across 12 angiosperm families using material collected in Illinois, fungal DNA contaminated over 60% of the templates analyzed. Endophytic fungi often are symptomless symbionts living within the above-ground tissues of their angiosperm hosts and are not affected by surface sterilization techniques. Recent studies have revealed their widespread occurrence and broad host range. We also present field strategies for obtaining plant material to reduce the possibility of collecting infected leaves and a simple screening test for detecting fungal DNA in angiosperm templates.     

Feeding behaviour and efficiency of banana weevil (Cosmopolites sordidus) larvae on banana cultivars of varying resistance levels

Nutrient composition, secondary plant substances and other host quality characteristics govern resistance and influence herbivore feeding. The current study was carried out to compare aspects of feeding behaviour and food utilization of banana weevil (Germar) (Coleptera: Curculionidae) larvae feeding on banana cultivars with different levels of resistance. In the first study, penetration times of larvae into tissue of seven banana cultivars (two susceptible, three intermediate and four resistant) were compared. Day‐old larvae were placed on corm or pseudostem tissue of these cultivars and time taken to penetrate the tissue was recorded. Larvae generally took longer to tunnel into resistant cultivars, although Yangambi Km5 (resistant) did not fit this pattern. In the second set of studies, food consumption and growth of larvae were compared on cultivars: (i) Kisubi (resistant) vs. Atwalira (susceptible); and (ii) Mbwazirume (intermediate) vs. Kayinja (resistant). Day‐old larvae were offered weighed pieces of corm that were changed every 4–7 days. At each corm change, weights of the larvae, corms and frass were measured. Changes in corm and larval weight were calculated to determine larval growth and amount of tissue consumed. Larvae feeding on resistant cultivars had lower consumption and growth rates and longer developmental duration. It was concluded that low food consumption rates contribute to delayed development of larvae feeding on resistant cultivars. Differences between resistant and susceptible cultivars in food utilization may be of limited consequence for the cultivars tested. This is one step in identifying the factors influencing weevil development rates in cultivars of different resistance levels. If these factors are identified, they can be targeted in breeding for resistance.     

Sterol content and efficiency of ion uptake by roots of maize genotypes

Data of compartmental analysis of sulphate were compared with the sterol content of roots of differently yielding maize genotypes. In conditions of steady state nutrient supply, sterol content was significantly correlated only with sulphate efflux (co). This increased at increasing concentration of sterols in the roots. Influx to cytoplasm (oc) was evaluated after sulphate deprivation leading to an induced rate of sulphate uptake. This was negatively correlated with sterol content, which was lower in the high than in the low yielding genotypes. When the highest yield genotype was grown at different sulphate concentrations, influx, efflux, root content of sulphate and sterols were positively correlated with the concentration of sulphate in the nutrient medium. Sterol content in roots appears to be controlled by both the genetic settlement and the nutritional status in maize. Low sterol content is connected with a high efficiency of sulphate utilization.     

Diversity and antimicrobial activity of endophytic fungi isolated from Nyctanthes arbor-tristis, a well-known medicinal plant of India

Endophytic fungi from Nyctanthes arbor-tristis were isolated and evaluated for their antimicrobial activity. A total of 19 endophytic fungi were isolated from 400 segments of healthy leaf and stem tissues of N. arbor-tristis. Eighteen endophytic fungi were obtained from leaf, while only ten from stem. Alternaria alternata had the highest colonization frequency (15.0%) in leaf, whereas Cladosporium cladosporioides ranked first in stem with a colonization frequency of 12%. The diversity and species richness were found higher in leaf tissues than in stem. The similarity indices between leaf and stem were 0.473 for Jaccard’s and 0.642 for the Sorenson index, respectively. Of 16, 12 (75%) endophytic fungal extracts showed antibacterial activity against either one or more pathogenic bacteria. The endophytic Nigrospora oryzae showed maximum inhibition against Shigella sp. and Pseudomonas aeruginosa. The leaf endophytes Colletotrichum dematium and Chaetomium globosum exhibited a broad range of anibacterial activity and were active against Shigella flexnii, Shigella boydii, Salmonella enteritidis, Salmonella paratyphi, and P. aeruginosa. Nine out of 16 (56.25%) endophytic fungi exhibited antifungal activity to one or more fungal pathogens. Colletotrichum dematium inhibited 55.87% of the radial growth of the phytopathogen Curvularia lunata. The antimicrobial activity of these endophytic microorganisms could be exploited in the biotechnological, medicinal, and agricultural industries.     

Biological control of maize seed pathogenic fungi by use of actinomycetes

The effectiveness of twoStreptomyces spp. strains to controlpathogenic fungi was studied in stored maizegrain. The treatments included seeddisinfection and inoculation withStreptomyces spp. strains previously isolatedfrom maize rhizosphere. Actinomycete inoculumconsisted of filtered suspension and totalsuspension of fermentor-producedStreptomyces spp. strains biomass. Treatmentswith Streptomyces spp. strains aloneeffectively suppressed the development ofAspergillus spp., Curvularia lunata, andDrechslera maydis and significantly(p < 0,05) reduced the incidence ofFusarium subglutinans and Cephalosporiumacremonium. Among the inoculation treatments,nondisinfested seed inoculated with filteredsuspension was the only treatment that did notsuppress the development of Penicilliumspp. Maize seed inoculation with totalsuspension of strains was the most effectivetreatment to control the incidence of seedpathogenic fungi. The development of theDiplodia maydis was only suppressed by thecombination of seed disinfection andinoculation with total suspension of strains.Although, the strain DAUFPE 11470 showed thegreatest effectiveness for controlling thefungi pathogenic to seed, root and shootdevelopment was reduced by treatment with thisstrain.The results indicate thatStreptomyces spp. strains reduce the incidenceof seed pathogenic fungi and have potential asa biological control agent. However, an efficient methodof seed treatment with the biological controlagent must be developed before it can become anagricultural practice.     

Seasonal and temporal dynamics of arbuscular mycorrhizal and dark septate endophytic fungi in a tallgrass prairie ecosystem are minimally affected by nitrogen enrichment

Root colonization by arbuscular mycorrhizae (AM) and dark septate endophytic (DSE) fungi in nitrogen amended and unamended mixed tallgrass prairie communities were analyzed monthly over two growing seasons. Roots were stained with Trypan blue and Sudan IV and fungal structures quantified using the modified magnified intersections method. Root length colonized (RLC) by DSE exceeded AM colonization during early part of the growing season. Fungal colonization varied among the years and was greater in 2003 than in 2002. Seasonal variation among the months within a growing season was observed in 2002 but not in 2003 for both AM and DSE. AM fungi were most abundant during the peak growing season of dominant C₄ vegetation while DSE were most abundant during the early part of the growing season. Hyperparasitism of AM hyphal coils by melanized septate fungi was frequently observed and increased with AM coil frequency. Although nitrogen amendment had altered the plant community composition, it had no impact on the colonization by AM or DSE fungi.