Sensitivity of populations ofBotrytis cinerea to triazoles,benomyl and vinclozolin

Sensitivity of field isolates (121) ofBotrytis cinerea from France (1992), Germany (1979–1992), Israel (1990) and the Netherlands (1970–1989) to the triazoles tebuconazole and triadimenol, the benzimidazole benomyl and the dicarboximide vinclozolin were tested in radial growth experiments. Resistance to benomyl (in 21 to 100% of isolates tested) and vinclozolin (in 25 to 71% of isolates tested) was common in most countries. EC₅₀s (concentrations of fungicides inhibiting radial mycelial growth ofB. cinerea on B5-agar by 50%) for tebuconazole and triadimenol ranged between 0.01–1.64 and 0.4–32.6g ml^–1, respectively, and were log-normally distributed. The variation factor (ratio between EC₅₀s of the least and most sensitive isolate tested) amounts 164 and 82 for tebuconazole and triadimenol, respectively. These values are comparable to those for azole fungicides applied in control of other pathogens. Hence, variation in sensitivity to triazoles can probably not explain limited field performance of triazoles towardsB. cinerea. Isolates from south west Germany (1992) were significantly less sensitive to tebuconazole than isolates collected earlier in Germany, Israel and the Netherlands. Such less sensitive populations may contribute to the limited field performance of DMI fungicides towardsB. cinerea. The sensitivity of isolates from south west Germany to tebuconazole was similar to that of DMI-resistant mutants generated in the laboratory. These mutants displayed stable resistance with Q-values (ratio between EC₅₀ of resistant mutant and wild type isolate) between 5 and 20. Sensitivity of field isolates and laboratory mutants to tebuconazole and triadimenol was correlated.     

Secretion of Natural and Synthetic Toxic Compounds from Filamentous Fungi by Membrane Transporters of the ATP-binding Cassette and Major Facilitator Superfamily

This review provides an overview of members of the ATP-binding cassette (ABC) and major facilitator superfamily (MFS) of transporters identified in filamentous fungi. The most common function of these membrane proteins is to provide protection against natural toxic compounds present in the environment of fungi, such as antibiotics produced by other microorganisms. In plant pathogenic fungi, these transporters can also be an important determinant of virulence on host plants by providing protection against plant defence compounds or mediating the secretion of host-specific toxins. Furthermore, they play a critical role in determining base-line sensitivity to fungicides and other antimycotic agents. Overexpression of some of these transporters can lead to the development of resistance to chemically-unrelated compounds, a phenomenon described as multidrug resistance (MDR). This has been observed in a variety of organisms and can impose a serious threat to the effective control of pathogenic fungi.     

Functional Analysis of ABC Transporter Genes From Botrytis cinerea Identifies BcatrB as a Transporter of Eugenol

The role of multiple ATP-binding cassette (ABC) and major facilitator superfamily (MFS) transporter genes from the plant pathogenic fungus Botrytis cinerea in protection against natural fungitoxic compounds was studied by expression analysis and phenotyping of gene-replacement mutants. The expression of 11 ABC (BcatrA–BcatrK) and three MFS genes (Bcmfs1, Bcmfs2 and Bcmfs4) was studied. All genes showed a low basal level of expression, but were differentially induced by treatment with cycloheximide and the plant defence compounds camptothecin, eugenol, psoralen, resveratrol and rishitin. The latter compounds induced expression of BcatrB at a high level. Eugenol was more toxic to BcatrB gene-replacement mutants than to the control isolates. Eugenol also caused an instantaneous increase in mycelial accumulation of the fungicide fludioxonil, a known substrate of BcatrB. However, there was no difference in virulence between the wild-type and BcatrB gene-replacement mutants on Ocimum basilicum, a plant known to contain eugenol. The results indicate that BcatrB is a transporter of lipophilic compounds, such as eugenol, but its role in virulence remains uncertain.     

腐霉对甲霜灵抗性测定及其生物防治

测定了腐霉属的8个种209个菌株对甲霜灵在浓度为0.5和50ug/ml时的抗性，从实验中观察到不同菌株对甲霜灵抗性变化的范围非常大，有95株在0.5ug/ml时，菌丝即停止生长，在20株在50ug/ml时，菌丝生长速度与对照几乎一样。经鉴定，这209株菌中，优势种为终极腐霉(Pythium ultimum）和刺腐霉(P.spinosum)。20株高抗菌中,P.ultimum占16株，P.irregulare占2株，P.spinosum和P.graminicola各占1株。盆栽试验表明：假单胞菌株Pseudomonas sp.CR56对高抗菌株P.ultimum ONCUR01引起黄瓜苗期猝倒病具有显著的防效，防效与甲霜灵和五氯硝基苯相比，达到极显著差异。     

The absolute configuration of chiral organophosphorus anticholinesterases

Contrary to an earlier report in this journal by Wustner and Fukuto (1), bovine erythrocyte acetylcholinesterase is inhibited preferentially by the same (S)_P-isomers of the two closely related anticholinesterases O-2-butyl S-2-(dimethylammonium)-ethyl ethylphosphonothioate hydrogen oxalate(I) and O-isopropyl S-2-(trimethylammonio)ethyl methylphosphonothioate iodide(II).     

Assessment of allometric algorithms for estimating leaf biomass, leaf area index and litter fall in different-aged Sitka spruce forests

The relationship between leaf area and diameter at breast height(d.b.h.) or sapwood area (AS) has been used to estimate standleaf area or biomass of forest canopies. It has been suggestedthat intra-specific variations in the relationship between standleaf area and d.b.h. or AS can introduce a systematic errorin these estimates for younger and older stands unless additionalparameters relating to canopy structure are included in allometricfunctions. We collected data from a Sitka spruce chronosequenceto parametrize and test different algorithms for the estimationof foliar biomass (FB) and litter inputs over a range of forestages. FB estimates were significantly improved when additionalbiometric information relating to crown structure (canopy opennessand height of live crown) was included in the models. Althoughthe use of the relationship between leaf area and AS for theestimation of leaf area is justified by theoretical considerations(pipe model theory), we show that d.b.h. and other canopy parametersprovided the most robust estimation of leaf area across different-agedstands. Our results also suggest that the accuracy of litterinput estimates depends on needle retention time and annualturnover rate, particularly immediately before and after canopyclosure.     

CIMMYT's approach to breeding for wide adaptation

Summary The wheat area in developing countries, including China, is around 100 million ha. To address the needs of these very diverse wheat growing areas, CIMMYT has defined 12 wheat mega-environments (ME). A ME is defined as broad, not necessarily continuous often transcontinental area with similar biotic and abiotic stresses, cropping systems and consumer preferences. The factors describing each ME are presented.CIMMYT's breeding methodology is centered around the development of widely adapted germplasm with high and stable yield across a wide range of environments. Segregating populations are alternating screened in two diverse environments in Mexico. One key requirement is that all germplasm is tested under near optimum conditions for its yield potential. The second one is multi-locational testing of advanced lines at sites that represent a given ME (key locations) and careful screening of germplasm for tolerance to abiotic and biotic stresses specific to that environment. This methodology has permitted the pyramiding of a large number of multiple resistance genes for use against a wide spectrum of diseases and tolerance to abiotic stresses within each ME. In addition, the widespread testing of lines allows the identification of traits which are beneficial in several environments. Data from international nurseries are used to further delineate environments within an ME. This approach has proven to be successful since around 70% of the spring wheat area in developing countries (excluding China) is planted to varieties derived directly or indirectly from CIMMYT germplasm. The performance of the bread wheat cultivar Pastor in international trials is given as an example for a wide adaptation.