Phylogenomic Analysis of a 55.1-kb 19-Gene Dataset Resolves a Monophyletic Fusarium that Includes the Fusarium solani Species Complex

Scientific communication is facilitated by a data-driven, scientifically sound taxonomy that considers the end-user's needs and established successful practice. In 2013, the Fusarium community voiced near unanimous support for a concept of Fusarium that represented a clade comprising all agriculturally and clinically important Fusarium species, including the F. solani species complex (FSSC). Subsequently, this concept was challenged in 2015 by one research group who proposed dividing the genus Fusarium into seven genera, including the FSSC described as members of the genus Neocosmospora, with subsequent justification in 2018 based on claims that the 2013 concept of Fusarium is polyphyletic. Here, we test this claim and provide a phylogeny based on exonic nucleotide sequences of 19 orthologous protein-coding genes that strongly support the monophyly of Fusarium including the FSSC. We reassert the practical and scientific argument in support of a genus Fusarium that includes the FSSC and several other basal lineages, consistent with the longstanding use of this name among plant pathologists, medical mycologists, quarantine officials, regulatory agencies, students, and researchers with a stake in its taxonomy. In recognition of this monophyly, 40 species described as genus Neocosmospora were recombined in genus Fusarium, and nine others were renamed Fusarium. Here the global Fusarium community voices strong support for the inclusion of the FSSC in Fusarium, as it remains the best scientific, nomenclatural, and practical taxonomic option available.

Clonality, spatial structure, and pathogenic variation in Fusarium fujikuroi from rain-fed rice in southern Laos

Bakanae disease, caused by the fungal phytopathogen Fusarium fujikuroi, can be detected in most rice (Oryza sativa L.) growing areas worldwide. In this study, we investigated the population structure of this fungus in southern Lao PDR, a country located near the geographic origin of rice domestication. Microsatellites (SSRs) and mating type (MAT) analyses, pathogenicity and fungicide sensitivity tests were integrated in the study. The first key finding is that the population genetic structure of F. fujikuroi in Lao PDR is consistent with high clonal reproduction. Indeed, (i) “true” clones were identified; (ii) within populations, MAT types were frequently skewed from 1:1 ratio, (iii) linkage disequilibrium (among SSRs as also among SSRs and MAT) was present, and (iv) gene-flow between opposite MAT types within the same population is restricted. The presence of genetic divergence among areas and populations and the occurrence of positive spatial autocorrelation of genetic variation, indicate that migration is restricted, and that genetic drift plays an important role in the evolution of this fungus. Two main well-defined groups of isolates were detected (F_ST = 0.213) that display a non-random spatial distribution. They differ in the ability to induce seedlings death but not seedlings elongation (the typical Bakanae symptom) suggesting that the pathogen’s ability to induce the two symptoms is under different genetic control. Finally, we compared two agroecosystems with contrasting characteristics: low-input and traditional (Lao PDR) vs high-input and modern (Italy). We found differences in the level of population structuring and of spatial autocorrelation. This suggests that the evolutionary potential of the fungus not only depends on its intrinsic characteristics, but is strongly influenced by other external factors, most likely by the dynamics of infested seed exchange. Thus, quarantine and chemical treatments are a way to reduce population connectivity and hence the evolutionary potential of this pathogen.

Monitoring of Fusarium Species and Trichothecene Genotypes Associated with Fusarium Head Blight on Wheat in Hebei Province, China

To clarify the changes in field populations of Fusarium head blight (FHB) pathogens over a decade, Fusarium species and trichothecene genotypes associated with FHB on wheat were monitored in Hebei province during the periods 2005–2006 and 2013–2016. Fusarium species determination was carried out by morphological identification, species-specific amplification and partial translation elongation factor (TEF-1α) gene sequencing. Trichothecene genotype prediction was carried out by primers 3CON/3NA/3D15A/3D3 or Tri13F/Tri13R, Tri303F/Tri303R and Tri315F/Tri315R. A total of 778 purified Fusarium isolates were recovered from 42 sampling sites in 17 counties during the period 2005–2006 and 1002 Fusarium isolates were recovered from 122 sampling sites in 65 counties during the period 2013–2016. F. graminearum was the predominant pathogen recovered during the periods 2005–2006 and 2013–2016. However, the pathogen composition differed slightly between the two periods. In 2005–2006, 752 out of 778 (96.7%) of the isolates belonged to F. graminearum. Two were identified as F. culmorum. Five other Fusarium species were also recovered, F. equiseti, F. verticillioides, F. proliferatum, F. subglutinans and F. chlamydosporum, with lower recoveries of 0.4%, 0.8%, 0.8%, 0.1% and 1.0%, respectively. Trichothecene genotype prediction showed that all the 752 F. graminearum isolates were of the 15-ADON genotype. Five Fusarium species were recovered from samples collected over the period 2013–2016. F. graminearum was again the predominant pathogen with an isolation frequency of 97.6%. F. pseudograminearum, F. asiaticum, F. culmorum and F. negundis were also isolated at a recovery of 1.4%, 0.7%, 0.2% and 0.1%, respectively. For the 2013–2016 isolates, 971 of the 978 F. graminearum strains were 15-ADON whereas seven isolates were of the 3-ADON type. All seven F. asiaticum isolates were of the NIV type and fourteen F. pseudograminearum isolates were classified as 3-ADON. F. pseudograminearum was first isolated from FHB in Hebei in 2013. Although the recovery of F. pseudograminearum is still low, it represents a small shift in the pathogen composition and trichothecene genotypes associated with FHB in Hebei province. As Fusarium crown rot of wheat caused by F. pseudograminearum is an increasing problem in Hebei province, it is appropriate to monitor the role of F. pseudograminearum in FHB in the future.

Genealogical concordance phylogenetic species recognition in the Fusarium oxysporum species complex

Fusarium oxysporum is an important plant and human pathogenic ascomycetous group, with near ubiquity in agricultural and non-cultivated ecosystems. Phylogenetic evidence suggests that F. oxysporum is a complex of multiple morphologically cryptic species. Species boundaries and limits of genetic exchange within this complex are poorly defined, largely due to the absence of a sexual state and the paucity of morphological characters. This study determined species boundaries within the F. oxysporum species complex using Genealogical Concordance Phylogenetic Species Recognition (GCPSR) with eight protein coding loci. GCPSR criteria were used firstly to identify independent evolutionary lineages (IEL), which were subsequently collapsed into phylogenetic species. Seventeen IELs were initially identified resulting in the recognition of two phylogenetic species. Further evidence supporting this delineation is discussed.

One fungus, one name: defining the genus Fusarium in a scientifically robust way that preserves longstanding use

In this letter, we advocate recognizing the genus Fusarium as the sole name for a group that includes virtually all Fusarium species of importance in plant pathology, mycotoxicology, medicine, and basic research. This phylogenetically guided circumscription will free scientists from any obligation to use other genus names, including teleomorphs, for species nested within this clade, and preserve the application of the name Fusarium in the way it has been used for almost a century. Due to recent changes in the International Code of Nomenclature for algae, fungi, and plants, this is an urgent matter that requires community attention. The alternative is to break the longstanding concept of Fusarium into nine or more genera, and remove important taxa such as those in the F. solani species complex from the genus, a move we believe is unnecessary. Here we present taxonomic and nomenclatural proposals that will preserve established research connections and facilitate communication within and between research communities, and at the same time support strong scientific principles and good taxonomic practice.

Fusarium: a ubiquitous fungus of global significance

Fusarium is one of the most economically important genera of fungal plant pathogens, causing significant crop losses and contamination of grain by mycotoxins on a global basis. Some species also cause infections (mycoses) of humans and other animals. Fusarium includes many species, a significant number of which cause a wide range of plant diseases that affect many crops including major food and fibre crops such as wheat, barley, maize, bananas and cotton, often with devastating socio-economic impact. The diseases are often insidious and extremely difficult to control. Its success as a plant pathogen can be attributed to wide host ranges, endophytic infection, and varied modes of survival and dispersal. Representatives occur in virtually all bioclimatic regions of the world in agricultural and natural ecosystems. In this article we present a summary of the key aspects of the biology and morphology of Fusarium and then briefly discuss several plant diseases to illustrate the diverse nature and devastating effects of these fungi, their mycotoxins, the impact of no-till farming systems on disease incidence, and the poorly understood but key role of endophytic colonisation in the disease cycle. Inevitably, the coverage is selective but it indicates the potential global impact of this fungal genus on plant disease and food security.

High levels of diversity in Fusarium oxysporum from non-cultivated ecosystems in Australia

The Fusarium oxysporum species complex (FOSC) is a ubiquitous ascomycetous group that includes both pathogenic and non-pathogenic strains, the former being responsible for disease in over 100 cultivated plant species. Previous phylogenetic studies have uncovered at least four major clades within the FOSC, with Clade 1 hypothesised as being ancestral. However, the origin of these clades and pathogenic strains is poorly understood. Due to an emphasis on agricultural isolates in previous studies, the underlying diversity of this species complex in non-cultivated soils is largely unknown. To address this imbalance an extensive survey of isolates associated with native vegetation geographically isolated from cultivation throughout the Australian continent was conducted. A multi-gene phylogenetic analysis of the translation elongation factor (EF-1α) and the mitochondrial small subunit (mtSSU) rDNA loci did not recover any novel clades. However, the Australian isolates had high levels of intra-Clade diversity based on EF-1α sequence type (ST) comparison with a global dataset. The ST diversity was not equally distributed across the four clades, with the majority of novel STs recovered from Clade 1. Implications on the origin of the FOSC are discussed.

Genetic structure of Fusarium pseudograminearum populations from the Australian grain belt

Crown rot, caused by the fungus Fusarium pseudograminearum (teleomorph Gibberella coronicola) is a major disease of wheat in the Australian grain belt. However, there is little information available on the population structure of this pathogen. We measured genetic diversity as assessed with amplified fragment length polymorphism (AFLP) analysis within and between populations of F. pseudograminearum from northeastern, south central, and southwestern regions of the Australian grain belt. Amongst the 217 isolates, 176 haplotypes were identified and grouped into two main clusters. One cluster contained isolates from populations in northeastern Australia, and the other cluster contained isolates from populations in south central and southwestern Australia. The southern populations were distinguished from the northeastern populations by higher levels of population differentiation (Gst) between them and genetic identity amongst the regional populations. We hypothesize that the F. pseudograminearum populations from northeastern and southern Australia are independent, which could result from different founding events or from geographic isolation and the accumulation of genetic differences due to genetic drift and/or selection.

Near-infrared emissions in single-bubble and multibubble sonoluminescence

Comparisons of light emissions from multibubble and single-bubble sonoluminescence in the near-infrared band extending from 800 to 1050 nm have been investigated. In argon-water mixtures, single-bubble and multibubble spectra are similar in appearance. In sodium chloride-water mixtures, the multibubble spectrum shows evidence of the 3d-3p sodium emission line, whereas the single-bubble spectrum shows no such emission. For single bubbles, the near-infrared emissions change linearly with driving pressure. No evidence of near-infrared emissions are observed below the visible luminescence threshold.

Cooperative effects in multi-bubble sonoluminescence

Theoretical and experimental evidence is presented in support of quantum collective effects in sonoluminescence.

Low-coherence interferometry in random media. I. Theory

We present a new nonperturbative theoretical method for the analytical description of light propagation in random multiscattering media. The method is illustrated through the calculation of an expression that describes optical backscattering from a semi-infinite disordered medium. A companion paper [J. Opt. Soc. Am. A 17, 2034 (2000)] compares the theoretical expression with experimental data.

Low-coherence interferometry in random media. II. Experiment

We present experimental results of measurements of light backscattering from semi-infinite disordered media by low-coherence interferometry (LCI). These results are compared with the theory developed in part I [J. Opt. Soc. Am. A 17, 2024 (2000)]. A comparison of the experimental data with the theoretical formulas based on the coherent phase approximation allows us to extract substantial information about the structure of the studied media. Our results demonstrate that LCI is an effective optical technique for studying nonuniform media even in the case in which the dimensions of nonuniformities are much less than the wavelength of the scattered light.

A Raman waveguide detector for liquid chromatography

A novel real-time liquid core Raman waveguide detector designed for liquid chromatographic applications is described. The Raman waveguide detector provides enhanced selectivity over typical high-performance liquid chromatography (HPLC) detectors. The waveguide detector also greatly improves the sensitivity of a typical Raman measurement without resorting to surface enhancement or resonance approaches and is compatible with the typical peak width volumes eluted by microbore and minibore HPLC (packed 1-2-mm-i.d. columns). Detection limit enhancements of over 1000-fold have been achieved for the measurement of alcohols in the aqueous phase with the Raman cell utilizing liquid core waveguide technology. The liquid core waveguides demonstrated in this study were constructed using Teflon AF 2400 tubing with a refractive index of 1.29. The low refractive index of the polymer material allowed HPLC separations with Raman detection to be performed with an aqueous mobile phase. A calibration curve for aqueous solutions of 2-propanol was generated and a limit of detection (LOD) of 2 ppm was determined. The Raman waveguide detector is demonstrated for the HPLC analysis of alcohol test mixtures, with LODs in the low-ppm range at the detector. By coupling the temporal separation achieved by HPLC with the vibrational information gleaned from Raman detection, an information-rich multivariate data matrix is obtained that can be deconvoluted to provide chemical speciation even when the HPLC resolution is poor. In this paper, we will discuss the physical and optical design of the Raman waveguide detector and the demonstration of the detector for HPLC detection.

Reaction of Australian cultivars of oats and barley to infection by Fusarium graminearum Group 1

The incidence of infection by Fusarium graminearum Group 1 and the incidence of crown rot were compared for various cultivars of oats, wheat and barley in glasshouse and field experiments. In glasshouse studies, the incidence of infected plants was lower in oats than in wheat or barley at 6 weeks after sowing. Crown rot symptoms were not observed in oats of any cultivar. The incidence and severity of crown rot in barley was similar to that in wheat cv. Banks. Between 17 and 29 genotypes of oats, wheat and barley were assessed in field trials over 3 years. Stem browning, a symptom of crown rot, was common in wheat and barley but was not observed in any cultivar of oats. Among plants of wheat and barley, the effect of cultivar on incidence of crown rot was significant (P = 0.05) in 3 of 4 trials. Results suggest that oats are a symptomless host. This should be considered when growing oats in rotation to reduce crown rot inoculum. The barley cultivars assessed all developed moderate-severe crown rot symptoms and thus may incur yield limitations where crown rot is prevalent.

Toxicity and trichothecene production by Fusarium acuminatum subsp. acuminatum and Fusarium acuminatum subsp. armeniacum

The toxicity of cultures of Fusarium acuminatum subsp. acuminatum and Fusarium acuminatum subsp. armeniacum grown on Weet-Bix medium was assessed using a chick bioassay. Thirty-nine of 45 cultures of F. a. armeniacum tested produced at least 50% mortality in the chick bioassay. In contrast, of the 26 cultures of F. a. acuminatum tested, only nine produced at least 50% mortality. Selected extracts of both subspecies were analyzed by gas chromatography after clean-up and hydrolysis for the four main trichothecene families, namely; nivalenol (NIV), deoxynivalenol (DON), scirpentriol (Sctol), and T-2 tetraol (T-2tol). Levels of up to 500 micrograms/g and 7 micrograms/g of T-2tol were detected in F. a. armeniacum and F. a. acuminatum extracts respectively. Four cultures each of F. a. armeniacum and F. a. acuminatum were also grown on two solid media (Weet-Bix and Vermiculite) and two liquid media (MYRO and GYEP). Culture extracts were again tested for toxicity and analyzed for trichothecene production. Cultures of F. a. armeniacum grown on the solid media and on MYRO produced the highest toxicity. Levels of up to 168, 129, 150, and 8 micrograms/g of T-2tol were detected in cultures of F. a. armeniacum on Weet-Bix, Vermiculite, MYRO, and GYEP respectively. In contrast, only trace amounts of T-2tol were detected in extracts of F. a. acuminatum on all media. Sctol levels of less than 0.5 microgram/g were also detected in some cultures of both subspecies on solid media, but only F. a. armeniacum produced trace levels of Sctol on liquid media.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term effects of stubble management on the incidence of infection of wheat by Fusarium graminearum Schw. Group 1

The effect of 3 stubble management regimes (burning after harvest, incorporation with a disc plough, retention on the surface) on the incidence of infection of wheat with Fusarium graminearum Schw. Group 1 was studied for 5 seasons at 2 sites at Moree, New South Wales. One site had high initial incidence (site A) and the other low initial incidence (site B). There were no differences in incidence of infection between retained and incorporated treatments. Stubble burning reduced the increase in incidence of infection in 2 of 5 years at site A and 3 of 4 years at site B. Failure of control in other years was attributed to susceptible weed hosts and poor burns. When stubble was retained on the plots at site B that had been burnt, incidence of infection in the next season increased to a level not significantly different from the retained or incorporated treatments. Incidence of infection at the fourth consecutive wheat crop at both sites was close to the maximum recorded, which was 92% at site A and 65% at site B. There was no evidence of a decline in incidence by the time of the most recent season assessed (eighth year of continuous wheat cultivation at site A, and sixth year at site B). In most years, the differences in yield between treatments were not significant.

The incidence and spatial patterns of wheat plants infected by Fusarium graminearum group 1 and the effect of crown rot on yield

The incidence and spatial patterns of wheat plants infected by Fusarium graminearum Group 1 were assessed in six fields in northern New South Wales, Australia, over a four-year period. The incidence of infected plants declined from 1978 to 1981 in fields where wheat was sown each year, where there was a bare fallow of 18 months and where sunflowers were sown in one season. The pattern of infected plants tended to be regular (uniform) where the incidence of infected plants was particularly high (> 96%). In all fields where a clustered (aggregated) pattern was detected, 12% to 64.4% of plants were infected. A random pattern was observed at a number of sites. There was a positive association between loss in potential yield and the incidence of infection, basal browning of plants and whiteheads. Losses of up to 89% were recorded.

Survey of the incidence of whiteheads in wheat crops grown in northern New South Wales, 1976-1981

The incidence of whiteheads in wheat in the northern areas of the wheat belt in New South Wales was surveyed from 1976 to 1981. Whiteheads were associated with plants affected by crown rot and were common in wheat crops in the survey areas, although the incidence was low (<5%) in most crops. There was a high incidence of whiteheads (>5%) in a small number of crops in each year. The mean incidence of whiteheads was highest in 1977 and was generally higher in the western, lower rainfall areas than in the other areas each year. The predominant crown rot pathogen Fusarium graminearum Group 1 was isolated from 97% of 1450 stem bases collected from plants with whitehead symptoms. A fallow of 18 months was not always associated with a reduction in the incidence of whiteheads.

Induction of heat stress in beef cattle by feeding the ergots of Claviceps purpurea

Two groups of 4 Hereford steers were housed in a controlled environment room and exposed to simulated high summer temperatures. Both groups were fed a barley grain and hay diet ad libitum. The barley in one diet contained 0.5% w/w ergots of Claviceps purpurea. Within one week of feeding the ergot diet mean rectal temperature was significantly elevated (P less than 0.05) each afternoon (up to 41 degrees C) but returned to normal overnight. Elevated rectal temperature was accompanied by other signs of heat stress, reduced feed intake, body weight loss and depression or serum prolactin concentration. Symptoms disappeared within 1 week of ceasing to feed the ergot diet.

The incidence of crown rot in wheat, barley and triticale when sown on two dates

Thirteen bread wheat cultivars, a durum wheat, a barley and a triticale cultivar were assessed in the field for their reaction to crown rot (Fusarium graminearum Group 1), based on the incidence of basal browning. Plots were sown in May and again in July at 2 sites i n northern New South Wales where the incidence of crown rot was high in the previous year. The incidence of infected plants and the incidence of plants with basal browning tended to be higher in all cultivars when sown in May. There was a mean loss in potential yield at 1 site of 35% and 18% at the other site. However, the mean loss in potential yield was unaffected by sowing date.

The impact of stubble management on the incidence of crown rot of wheat

The influence of 3 stubble management practices, stubble retention, stubble incorporation and stubble burning, on the incidence of crown rot of wheat (Triticum aestivum L.) caused by Fusarium graminearum Schwabe Group 1, and on plant development and grain yield was examined. The incidence of disease (percentage plants affected) was assessed in a susceptible (cv. Sunstar) and moderately resistant cultivar (cv. Suneca) in 1986. In 1987 Sunstar was planted into stubble of the 2 cultivars to assess the influence of host resistance on disease carryover. Crown rot was highest in the stubble retention plots (81% incidence in 1986 and 59% in 1987), whereas stubble burning decreased disease incidence in both years, with the reduction being greater in the second year (47% and 16%). Stubble incorporation was ineffective in reducing disease levels (76% and 53% in years 1 and 2). The incidence of crown rot did not differ in the 2 cultivars. At the harvest sampling in 1987 there were no differences in crown rot incidence in plants sown into stubble of the 2 cultivars. Grain yield did not differ significantly between treatments, but early season plant dry weight was reduced in the retained plots. Grain protein levels were reduced (P< 0.05) in the stubble burnt plots.

Oxalate uptake by everted sacs of rat colon. Regional differences and the effects of pH and ricinoleic acid

Hyperoxaluria is a complication of disorders associated with steatorrhea. The colon is the presumed site of enhanced oxalate absorption in patients with steatorrhea. We performed studies of colonic mucosal oxalate uptake in everted sacs of rat colon to determine the kinetics of colonic oxalate transport and to evaluate the effect of both pH and ricinoleic acid, a hydroxy fatty acid, on colonic oxalate uptake. Our study demonstrated that oxalate is transported throughout the colon by passive diffusion. Tissue uptake increased linearly with increasing oxalate concentrations and was unaffected by metabolic inhibitors, oxygen deprivation, or temperature changes. There were pH-dependent regional differences of oxalate uptake both in the presence and absence of ricinoleic acid. In the absence of ricinoleic acid, the highest oxalate uptake occurred at the lower pH values (5.4 and 6.4). In the presence of ricinoleic acid oxalate uptake was enhanced at the higher pH values (7.4 and 8.4); a finding most likely related to decreased solubility of ricinoleic acid at pH 5.4 and 6.4. Intraluminal pH is an important determinant of colonic oxalate uptake in the presence and absence of ricinoleic acid.

Surveys of Fusaria associated with crown rot of wheat in eastern Australia

Fusavium voseum 'Graminearum' was found to be the predominant fusarium associated with crown rot of wheat in the eastern wheat belt of Australia. This conclusion was based on quantitative surveys involving isolations from stem bases of crown rot-affected plants at growth stages 10.5-11 which were collected at random in the 1972, 1973 and 1974 growing seasons. The majority of the isolates of F. roseum 'Graminearum' did not form perithecia in culture or on sterile wheat straw and are referred to as group 1 isolates to distinguish them from group 2 isolates which normally form perithecia in culture. The two groups can also be distinguished on the basis of cultural characteristics. Several group 2 isolates were obtained from wheat stem bases. The results indicate that the incidence and severity of crown rot caused by F. roseum 'Graminearum' was greater in areas where plants were affected by low soil moisture. The disease was found to occur in all areas of the eastern wheat belt which were surveyed.

Surveys of Fusaria and other fungi associated with stalk rot of maize in Eastern Australia

Fusarium roseum 'Graminearum' was the predominant fungus associated with stalk rot of maize in eastern Australia in the 1972, 1973 and 1974 growing seasons. All isolates of this pathogen were of the group 2 type. Other fungi isolated in order of frequency were Diplodia maydis, F. moniliforme 'Subglutinans', Bipolaris sorokiniana, Nigrospora oryzae, F. roseurn 'Semitectum', F. moniliforme, F. roseurn 'Equiscti', F. roseum 'Concolor', Macrophominaphaseolina, Rhizoctonia sp., F. roseum 'Acuminatum', F. oxysporum, F. solani, F. tricincturn and F. roseum 'Heterosporum'. The relative isolation frequencies of the fungi varied according to the seasonal conditions. Stalk rots were not of major importance in 1973, a relatively dry growing season. However, in 1974, a wet growing season, stalk rot diseases were common in all areas.

The relationship between the spore density of Cochliobolus sativus in soil and its saprophytic activity and parasitism

Both saprophytic colonization of wheat straw and seedling infection by Cochlioholus sativus (Ito and Kur.) Drechsl. ex Dastur, which causes common root rot of wheat, were correlated with spore density. The results indicate that straw colonization is possible at 10�C even when the spore density is too low to cause seedling infection. Saprophytic activity may thus raise the spore density over the threshold necessary for parasitism.

The recovery of Gibberella zeae from wheat straws

Attempts were made to recover Gibberella zeae (Schw.) Petch, a soil fungus which attacks wheat, from wheat straws colonized by the fungus and subsequently exposed in contact with soil at different temperatures and soil moistures. In certain treatments, the fungus could still be recovered after two years. In general, however, recovery declined with time and was adversely affected when the straws were exposed to conditions favouring increased microbial activity (moist soil at relatively high temperatures).