Helen M. West

Influence of arbuscular mycorrhizal infection on competition between holcus lanatus and dactylis glomerata.

1 Holcus lanatus and Dactylis glomerata were grown in monocultures and mixtures to determine the influence of mycorrhizal fungi on intraand interspecific competition. 2 In monoculture, shoot biomass per plant of both species was increased over all densities by mycorrhizal infection. Increased tiller and leaf numbers per plant for H. lanatus, but not for D. glomerata, suggested that enhanced biomass was a result of greater tiller and leaf production in Holcus, but to increased tiller weight in Dactylis. Increased competition reduced shoot biomass, tiller number and leaf number in both species. 3 Although the response was variable, mycorrhizal infection generally enhanced shoot biomass of both species in mixed cultures. Tiller production in D. glomerata was generally unaffected by infection but reductions in leaf number were observed in mycorrhizal stands. In contrast to its effects on monocultures, infection had no effect on tiller production when H. lanatus was in mixture. 4 Relative yield totals (R YT) calculated for grasses grown in mixture suggest that, overall, mycorrhizal infection resulted in a reduction of resource complementarity, i.e. it increased the level of competition for the same resources. This was reflected in the relative yields which showed that the shoot biomass for each species in mixture was lower than that expected from growth in monoculture. 5 Aggressivity indices suggested that H. lanatus was more aggressive than D. glomerata when present in equal or greater numbers. Mycorrhizal infection altered the degree of aggressivity in favour of the already more aggressive plant within the combination, although, at very low densities, D. glomerata was more aggressive than H. lanatus when mycorrhizal.

The influence of three biocides on the fungal associates of the roots of Vulpia ciliata ssp. ambigua under natural conditions

The study of mycorrhizal function under field conditions would be greatly aided by a method for controlling infection in roots. The only feasible method at present is the use of fungicides. We have applied three functionally distinct fungicides (benomyl, procloraz and iprodione) to plants of the winter annual grass Vulpia ciliata ssp. ambigua growing both in the field and in a glasshouse. We measured the impact of the fungicides on mycorrhizal colonization, plant performance and on populations of other fungi both in the rhizosphere and the bulk soil. All biocides were effective in some circumstances in reducing mycorrhizal colonization of the roots, but benomyl was the most effective, followed by iprodione and procloraz. Only benomyl controlled infection in both field and glasshouse experiments (...)

Symbiotic fungi determine plant community structure: changes in a lichen-rich community induced by fungicide application

The fungicide benomyl was applied to a lichen-rich plant community growing on a sandy soil in Suffolk, UK, once a month from November to May for 3 years. Benomyl application eliminated the lichen Cladonia rangiformis from the community and resulted in a large increase in the cover of the moss Ceratodon purpureus. There were also changes in the frequencies of several higher plant species in response to benomyl application. There were significant reductions in mycorrhizal colonization following fungicide application in Crepis capillaris and Erodium cicutarium, which were reduced in abundance by benomyl application, whereas the non-mycorrhizal Arenaria serpyllifolia and Rumex acetosella increased in abundance in fungicide-treated plots. Changes in the frequencies of mycorrhizal higher plant species were negatively correlated with reductions in mycorrhizal colonization of their root systems. There was also a 22% increase in plant species density m -2 in plots treated with benomyl. Ordination analyses showed that 60% of the variation in the vegetation data set could be accounted for by Carex arenaria, Cladonia rangiformis and R. acetosella on the first component axis, and by Ceratodon purpureus, Hypnum cupressiforme var. lacunosum and Cerastium fontanum on the second axis, and demonstrated that the two sets of plots were vegetationally distinct. The results show that two groups of symbiotic fungi are important regulators of plant community structure: the lichen C. rangiformis was a keystone organism in the community studied and appeared to be able to suppress the moss C. purpureus, and arbuscular mycorrhizal fungi appeared to play a significant role in determining the interspecific competitive abilities of higher plant species.

Response of Vulpia ciliata ssp. ambigua to removal of mycorrhizal infection and to phosphate application under natural conditions

We have conducted a series of factorial experiments involving the application of the fungicide benomyl to reduce mycorrhizal infection, and of phosphate, to ascertain whether mycorrhizal fungi contribute to fitness in the winter annual grass Vulpia ciliata ssp. ambigua and whether any such contribution can be ascribed to increased P uptake. Experiments were set up at four sites in East Anglia (UK) where the grass grows with large differences in the natural intensity of mycorrhizal infection. At one site, the factorial experiment was nested within an irrigation treatment. In addition, we performed experiments to test the yield response of V. ciliata to added P. Plant response to P was slight: a small stimulus at very low addition rates and a depression at high rates (...)

Effects of polyamine biosynthesis inhibitors on growth of Pyrenophora teres, gaeumannomyces graminis, Fusarium culmorum and Septoria nodorum in vitro

The effects of a number of polyamine biosynthetic inhibitors on the growth of four species of necrotrophic fungi were examined in vitro . Additions of polyamines were also made to growth media, both alone and in combination with DFMO, the most widely studied inhibitor of polyamine biosynthesis, and their effects on fungal growth were examined. Species-dependent responses to the inhibitors were observed. DFMO was the least effective inhibitor. Some increases in growth were observed after treatment with inhibitors. This is possibly a result of secondary enzyme production or overproduction of the target enzyme, leading to an initial surge of polyamine synthesis and enhanced growth. The effects of DFMO could be reversed by the addition of polyamines to the growth medium.

Phosphorus recovery as struvite from farm, municipal and industrial waste: feedstock suitability, methods and pre-treatments

Global population growth requires intensification of agriculture, for which a sustainable supply of phosphorus (P) is essential. Since natural P reserves are diminishing, recovering P from wastes and residues is an increasingly attractive prospect, particularly as technical and economic potential in the area is growing. In addition to providing phosphorus for agricultural use, precipitation of P from waste residues and effluents lessens their nutrient loading prior to disposal. This paper critically reviews published methods for P recovery from waste streams (municipal, farm and industrial) with emphasis on struvite (MgNH4PO4·6H2O) crystallisation, including pre-treatments to maximise recovery. Based on compositional parameters of a range of wastes, a Feedstock Suitability Index (FSI) was developed as a guide to inform researchers and operators of the relative potential for struvite production from each waste.

Evaluation of photosynthetic potential of wheat genotypes under drought condition

Water availability is one of the most important limiting factors in agriculture worldwide, particularly in arid and semiarid regions. Six spring wheat genotypes, i.e. three UK cultivars Cadenza, Paragon, and Xi-19 and three synthetic-derived lines L-22, L-24, and L-38, were grown in a phytotron under well-watered (until 40 days after sowing) and drought conditions. The aim of the study was to evaluate the traits related to photosynthetic capacity (net photosynthesis rate, stomatal conductance, internal CO2 concentration, transpiration rate, carboxylation capacity, instantaneous and intrinsic water-use efficiency) and plant biomass production in the cultivars and synthetic derivatives of wheat genotypes under well-watered and water-limited conditions. Genotypic variations in gas-exchange traits including net photosynthetic rate, carboxylation capacity, instantaneous water-use efficiency, and biomass yield were found amongst genotypes. Drought significantly reduced the total dry matter per plant. The synthetic derivatives L-22 and L-24 showed higher performance of stomata for most of the stomatal aperture characteristics. Total dry matter was positively related to net photosynthetic rate and to instantaneous and intrinsic water-use efficiencies. Finally, net photosynthetic rate was also positively related to stomatal conductance and transpiration rate under both the well-watered and water-limited drought conditions.

Polyamine uptake by the plant pathogenic fungus, Fusarium culmorum

The uptake of putrescine and spermidine was studied in Fusarium culmorum using 14C-labelled polyamines. Polyamine uptake was pH-dependent and was biphasic, with Km values (m m ) for system 1 uptake of 0·17 (putrescine) and 0·34 (spermidine) and for system 2 uptake of 32·73 (putrescine) and 42·17 (spermidine). Uptake of putrescine and spermidine was increased by the presence of spermidine and putrescine, respectively, in the uptake medium and uptake of both amines was partially inhibited in the presence of 1 m m sodium azide. Growth of the fungus in media containing α-difluoromethylornithine resulted in small increases in polyamine uptake, although uptake was reduced when the pathogen was grown in the presence of methylglyoxal-bis (guanylhydrazone).

Pseudomonas and Burkholderia inhibit growth and asexual development of Phytophthora capsici

Abstract The objective of this study was to isolate and characterize antagonistic rhizobacteria from chili against a notorious phytopathogen Phytophthora capsici. Among the 48 bacteria isolated, BTLbbc-02, BTLbbc-03, and BTLbbc-05 were selected based on their inhibitory activity against P. capsici. They were tentatively identified as Burkholderia metallica BTLbbc-02, Burkholderia cepacia BTLbbc-03, and Pseudomonas aeruginosa BTLbbc-05, respectively, based on their 16S rRNA gene sequencing. All inhibited the growth of P. capsici at varying levels by inducing characteristic morphological alterations of P. capsici hyphae. The cell-free culture supernatant of all three isolates impaired motility (up to 100%) and caused lysis (up to 50%) of the halted zoospores. Bioassays revealed that Pseudomonas sp. had higher antagonism and zoospore motility-inhibitory effects against P. capsici compared with two other isolates, Burkholderia spp. and B. metallica, which caused vacuolation in mycelium. All three bacteria suppressed sporangium formation and zoosporogenesis of P. capsici, and improved the seed germination and growth of cucumber. Our findings suggest that epiphytic bacteria, B. metallica, B. cepacia, and P. aeruginosa, could be used as potential biocontrol agents against P. capsici. A further study is required to ensure conformity with the existing regulations for soil, plant, and human health.

Endophytic Bacillus spp. from medicinal plants inhibit mycelial growth of Sclerotinia sclerotiorum and promote plant growth

Abstract Plant growth-promoting bacteria that are also capable of suppressing plant pathogenic fungi play an important role in sustainable agriculture. There is a critical need for conducting research to discover, characterize and evaluate the efficacy of new strains of such bacteria in controlling highly aggressive plant pathogens. In this study, we isolated endophytic bacteria from medicinal plants of Bangladesh and evaluated their antagonistic capacity against an important phytopathogenic fungus Sclerotinia sclerotiorum. Growth-promoting effects of those isolates on cucumber and rice seedlings were also assessed. Among 16 morphologically distinct isolates, BDR-2, BRtL-2 and BCL-1 significantly inhibited the growth of S. sclerotiorum through induction of characteristic morphological alterations in hyphae and reduction of mycelial dry weight. When cucumber and rice seeds were treated with these endophytic bacteria, seven isolates (BCL-1, BDL-1, BRtL-2, BRtL-3, BDR-1, BDR-2 and BBoS-1) enhanced seed germination, seedling vigor, seedling growth and number of roots per plant at a varying level compared to untreated controls. All isolates produced high levels of indole-3-acetic acid (6 to 63 μg/mL) in vitro. Two most potential isolates, BDR-2 and BRtL-2, were identified as Bacillus amyloliquefaciens and B. subtilis, respectively, based on the 16S rRNA gene sequencing. These results suggest that endophytic Bacillus species from native medicinal plants have great potential for being used as natural plant growth promoter and biopesticides in sustainable crop production.