Evaluation of the Use of Ammonium Bicarbonate and Oregano (Origanum vulgare ssp. hirtum) Extract on the Control of Apple Scab

In vitro experiments showed that ammonium bicarbonate and aqueous extracts of oregano were effective in inhibiting conidia germination and germ‐tube elongation of Venturia inaequalis. Complete inhibition was achieved by 1% ammonium bicarbonate, 2% oregano extract and 0.01% synthetic fungicide difenoconazole. Two orchard experiments were conducted on the highly susceptible cv. Mutsu to apple scab to investigate the efficacy of ammonium bicarbonate alone or in combination with an aqueous extract of oregano for the control of apple scab. In 2008 and 2009, except for the applications of 1% aqueous extract of oregano, the applications of ammonium bicarbonate (0.5 and 1%) and difenoconazole (0.01%) to trees at 10‐day intervals significantly reduced disease incidence and severity on leaves and fruit compared to the water‐treated control. In both years, the efficacy of 0.5 and 1% ammonium bicarbonate in inhibiting both disease incidence and severity on leaves and fruit was equally effective in all monthly assessments from June to September. Combining 0.5 and 1% ammonium bicarbonate with 1% aqueous extract of oregano did not significantly improve the efficacy of stand‐alone applications of treatments in the final assessment in 2008 and 2009. All treatments were neither phytotoxic to leaves and fruit nor did they adversely affect quality parameters of fruit including physiological disorders and taste both at harvest and after storage. These results indicate that ammonium bicarbonate treatment may be applied as an alternative chemical for the control of apple scab.     

Efficacy of Boric Acid,Monopotassium Phosphate and Sodium Metabisulfite on the Control of Apple Scab

In vitro experiments indicated that boric acid, monopotassium phosphate, sodium metabisulfite and synthetic fungicide fluopyram + tebuconazole were effective in inhibiting conidia germination and germ‐tube elongation of Venturia inaequalis. Monopotassium phosphate even at the highest concentration used in the study reduced conidia germination and germ‐tube elongation of V. inaequalis by 22.1% and 28.8%, respectively; however, the difference between two compounds at lower concentrations except 0.05% (for conidia germination) and 0.1% (for germ‐tube elongation) of boric acid was statistically significant (P ≤ 0.05). Complete inhibition was achieved by 0.01% sodium metabisulfite, 0.035% fluopyram + tebuconazole and 0.2% boric acid. Two orchard trials were conducted on the highly susceptible cv. Mutsu to apple scab to ascertain the efficacy of 0.2% boric acid, 0.5% monopotassium phosphate, 0.5% sodium metabisulfite and 0.035% fluopyram + tebuconazole for the control of apple scab. In both 2013 and 2014, except for the applications of monopotassium phosphate and sodium metabisulfite, the applications of boric acid and fluopyram + tebuconazole to trees at 10‐day intervals significantly reduced disease incidence and severity on leaves and fruit compared to the water‐treated control. In both years, the efficacy of boric acid and fluopyram + tebuconazole treatments was similar in reducing both disease incidence and severity on leaves and fruit in all monthly assessments from July to September. All treatments were neither phytotoxic to leaves and fruit nor did they adversely affect quality parameters of harvested fruit. These results show that boric acid treatment may be applied as an alternative chemical for the control of apple scab.     

A detailed linkage map around an apple scab resistance gene demonstrates that two disease resistance classes both carry the V f gene

A detailed genetic map has been constructed in apple (Malus x domestica Borkh.) in the region of the v _f gene. This gene confers resistance to the apple scab fungus Venturia inaequalis (Cooke) Wint. Linkage data on four RAPD (random amplified polymorphic DNA) markers and the isoenzyme marker PGM-1, previously reported to be linked to the v _f gene, are integrated using two populations segregating for resistance to apple scab. Two new RAPD markers linked to v _f (identified by bulked segregant analysis) and a third marker previously reported as being present in several cultivars containing v _f are also placed on the map. The map around v _f now contains eight genetic markers spread over approximately 28 cM, with markers on both sides of the resistance gene. The study indicates that RAPD markers in the region of crab apple DNA introgressed with resistance are often transportable between apple clones carrying resistance from the same source. Analysis of co-segregation of the resistance classes 3A (weakly resistant) and 3B (weakly susceptible) with the linked set of genetic markers demonstrates that progeny of both classes carry the resistance gene.This work was supported in part by grants from the New Zealand Foundation for Research Science and Technology (FoRST) Programme 94-HRT-07-366 and ENZA New Zealand (International)     

Standard area diagrams to assess scab severity of entire-margined leaves of sour passion fruit

Scab caused by the Cladosporium cladosporioides complex is one of the most important diseases affecting passion fruit yield and fruit quality. Standard area diagrams are useful tools to improve the accuracy and reliability of the estimates of disease severity in many pathosystems. The interpretation of the accuracy of the resulting disease data may be the basis for providing better disease management. This study aimed to develop and validate standard area diagrams (SADs) to quantify scab severity of entire-margined leaves of sour passion fruit plants. The SADs are composed of ten images of scab severity values (0.4%, 3.5%, 5.4%, 8.0%, 11.1%, 16.2%, 26.1%, 38.2%, 47.9% and 58.9%). Twenty raters (ten experienced and ten inexperienced ones) evaluated the SADs. The raters estimated the same set of fifty images twice. In the examination, the SADs were used, while in the second examination, they were not used. Accuracy was significantly improved by using the SADs. The coefficients of bias (C_b) were 0.96 and 0.98 for the experienced raters and 0.75 and 0.98 for the inexperienced raters without and with SADs, respectively. The correlation coefficient (r) values were 0.95 and 0.97 for the experienced raters and 0.89 and 0.97 for the inexperienced raters without and with the use of the SADs, respectively. Lin's concordance correlation coefficient (ρ_c) values were 0.91 and 0.95 for the experienced raters and 0.66 and 0.95 for the inexperienced raters without and with the use of the SADs, respectively. Moreover, the coefficient of determination (R²) significantly improved when the SADs were used. The SADs proposed in this study, if properly used, may improve both the accuracy and reliability during the evaluation of scab severity of entire-margined leaves of sour passion fruit plants.     

Evaluation of microcapsule trunk injections for the control of apple scab and powdery mildew

A 3‐year field trial was conducted using established apple cv. Crown Gold and English oak (Quercus robur L.) to assess the efficacy of eight fungicides applied via microcapsule trunk injection against the foliar pathogens apple scab (Venturia inaequalis) and powdery mildew (Phyllactinia sp). In both apple cv. Crown Gold and English oak, the fungicide myclobutanil was not taken up when microcapsules were inserted into the tree vascular system at the root flare. Disease severity in injected trees, excluding myclobutanil, was lower over the following two growing seasons compared to water‐injected controls indicating seven of the eight fungicides used in this study provided a significant degree of protection against scab and powdery mildew infection. A difference in the magnitude of pathogen control achieved was recorded between fungicides. Of the fungicides tested, penconazole, pyrifenox and carbendazim significantly reduced disease severity and significantly increased leaf chlorophyll (Fv/Fm) and SPAD values as a measure of tree vitality and chlorophyll content, respectively, in both apple cv. Crown Gold and English oak over two growing seasons after microcapsule injection. Based on the results of this investigation, it is suggested that these three fungicides be used in preference to thiabendazole, fosetyl‐aluminium, triadimefon and propiconazole for the control of apple scab and powdery mildew where outbreaks of these foliar pathogens are problematic.     

Molecular configuration of amylose and its complexes in aqueous solutions. Part IV. Determination of DP of amylose by measuring the concentration of free iodine in solution of amylose–iodine complex

In aqueous solutions of the amylase–iodine complex the concentration of free iodine [I_f]_v after reaching equilibrium (or closely approximating it) is determined by the following factors: temperature, pH, concentration of iodide ions and amylose, and DP of amylose. In the present paper the role of temperature, amylose concentration, and DP has been investigated. At half-saturation of amylose by iodine, the reciprocal value of free iodine defines the equilibrium constant: 1/[I_f]_v = K. The relation between [I_f]_v, in normality and temperature is the following: 5 + log [I_f]_v = ?(2.132/T) + 8.52, for DP _n = 1290, 0.4 mg. amylose in 100 ml. 0.1N HCl. The value of the energy of activation E_a between 2 and 52°C. is 9.72 kcal./mole. The influence of amylose concentration [Am] on photometrically determined [I_f]_v, at 20°C, in the range of 0.1–1.2 mg./100 ml. 0.1 N HCl for DP _n = 1290 is: 5 + log [I_f]_v = 0.209 ? 0.047 log [Am]. At [Am] = 0.6 mg. amylose/ 100 ml. 0.1 N HCl and 20°C, the value of [I_f]_v depends on DP _n as follows: 5 + log [I_f]_v = 0.085 = + 0.222 log (10⁴/DP _n). These above equations are summarized by the relation: [I_f]_v = exp {16.865 ? (E_a/RT)}[Am]^0.047(10⁴/DP _n)^0.222 ×10^?5 Considering that the determination of [I_f]_v by automatic photometric titration can be performed quickly and with appropriate reproducibility, this method is convenient for a rapid empirical and approximate determination of DP of amylose on a microscale. The iodine-binding capacity [IBC] as well as the value of λ_max, have been also investigated as functions of DP _n, by photometric and by amperometric titration.     

An integrated approach with Trichoderma harzianum DGA01 and hot water treatment on control of crown rot disease and retention of overall quality in banana

A biological control of crown rot disease of banana fruit was analysed using an integrated approach combining hot water treatment and Trichoderma harzianum strain DGA01. Treated fruits were stored at 22–25 °C and 90–95% relative humidity for 2 weeks. The bioefficacy of fungal antagonist in vitro towards crown rot-causing pathogens, namely Lasiodiplodia theobromae, Thielaviopsis paradoxa, Colletotrichum musae and Fusarium verticillioides, was enhanced by 11.41% following hot water treatment (50 °C, 20 min). DGA01 germinated on the fruit 48 h after inoculation and parasitised the pathogen. Postharvest application showed that hot water treatment and conidial suspension of DGA01 (10⁶ ml^?1) applied singly performed significantly better than the untreated control in reducing the incidence of crown rot, but were not as effective as the fungicide. The combination of hot water treatment and DGA01 gave 93% control of fruit decay which was comparable with fungicide treatment of 95%. The quality of fruit was markedly improved in hot water treatment + DGA01 as compared to those dipped in fungicide solution. The inconsistencies of single treatments, by DGA01 or hot water dips, in controlling crown rot such as variation in severity of disease among treatments and within a treatment, were lessened by dipping the fruit in DGA01 conidial suspension following hot water treatment.     

Control and yield loss modelling of circular leaf spot of persimmon caused by Mycosphaerella nawae

Symptoms of circular leaf spot of persimmon (CLSP), caused by Mycosphaerella nawae, consisted of necrotic spots on leaves, chlorosis and premature defoliation. Although CLSP is a foliar disease, early fruit maturation and abscission are frequently associated with the presence of lesions on leaves and defoliation, resulting in severe economic losses. Despite their importance for the design of efficient disease management programmes, quantitative relationships between CLSP incidence and yield loss are unknown. Therefore, fungicide efficacy trials were conducted during two consecutive years in Spain to induce different levels of disease severity, defoliation and yield loss. The effects of fungicide treatments on CLSP severity were analysed by ordinal logistic regression models. Relative yield loss values were regressed against the percentage of affected leaves or defoliated obtained at different evaluation dates. The disease had high negative impact and complete yield loss was observed in the absence of effective fungicide treatments. Preventive applications of pyraclostrobin, trifloxy‐strobin and mancozeb provided the best disease control and highest yields, up to 95.77 kg tree^?1. An exponential relationship of CLSP incidence and defoliation with yield loss was found. In general, model fit and predictive ability was superior when defoliation, rather than incidence, was used as explanatory variable. The impact of defoliation on yield loss was higher in earliest evaluation dates, suggesting that early leaf abscission may be the main factor contributing to premature fruit drop and subsequent yield loss. Substantial yield losses were observed even with relatively low levels of CLSP incidence and defoliation. Therefore, it was not possible to define a critical action threshold for CLSP management based on foliar symptoms.     

Development and Validation of a Weather-Based Model for Predicting Infection of Loquat Fruit by Fusicladium eriobotryae

A mechanistic, dynamic model was developed to predict infection of loquat fruit by conidia of Fusicladium eriobotryae, the causal agent of loquat scab. The model simulates scab infection periods and their severity through the sub-processes of spore dispersal, infection, and latency (i.e., the state variables); change from one state to the following one depends on environmental conditions and on processes described by mathematical equations. Equations were developed using published data on F. eriobotryae mycelium growth, conidial germination, infection, and conidial dispersion pattern. The model was then validated by comparing model output with three independent data sets. The model accurately predicts the occurrence and severity of infection periods as well as the progress of loquat scab incidence on fruit (with concordance correlation coefficients >0.95). Model output agreed with expert assessment of the disease severity in seven loquat-growing seasons. Use of the model for scheduling fungicide applications in loquat orchards may help optimise scab management and reduce fungicide applications.     

Cesium,Na+-K+ pump and pacemaker potential in cardiac purkinje fibers

The mechanisms of the hyperpolarizing and depolarizing actions of cesium were studied in cardiac Purkinje fibers perfused in vitro by means of a microelectrode technique under conditions that modify either the Na⁺-K⁺ pump activity or I_f. Cs⁺ (2 mM) inconsistently increased and then decreased the maximum diastolic potential (MDP); and markedly decreased diastolic depolarization (DD). Increase and decrease in MDP persisted in fibers driven at fast rate (no diastolic interval and no activation of I_f). In quiescent fibers, Cs⁺ caused a transient hyperpolarization during which elicited action potentials were followed by a markedly decreased undershoot and a much reduced DD. In fibers depolarized at the plateau in zero [K⁺]_o (no I_f), Cs⁺ induced a persistent hyperpolarization. In 2 mM [K⁺]_o, Cs⁺ reduced the undershoot and suppressed spontaneous activity by hyperpolarizing and thus preventing the attainment of the threshold. In 7 mM [K⁺]_o, DD and undershoot were smaller and Cs⁺ reduced them. In 7 and 10 mM [K⁺]_o, Cs⁺ caused a small inconsistent hyperpolarization and a net depolarization in quiescent fibers; and decreased MDP in driven fibers. In the presence of strophanthidin, Cs⁺ hyperpolarized less. Increasing [Cs⁺]_o to 4, 8 and 16 mM gradually hyperpolarized less, depolarized more and abolished the undershoot. We conclude that in Purkinje fibers Cs⁺ hyperpolarizes the membrane by stimulating the activity of the electrogenic Na⁺-K⁺ pump (and not by suppressing I_f); and blocks the pacemaker potential by blocking the undershoot, consistent with a Cs⁺ block of a potassium pacemaker current.     

Analysis of Reproductive Parameters of Urban and Rural Population of Chuvashia

Genetic and demographic characteristics for urban and rural population of the Chuvash Republic (Chuvashes and Russians) were calculated based on 1122 questionnaires. The sibship sizes for Chuvashes were 2.05 (urban) and 2.78 (rural). For Russians these indices were 1.75 (urban) and 2.00 (rural), respectively. Crow’s index and its components were I _m = 0.04; I _f = 0.18; and I _tot = 0.22 for urban, and I _m = 0.07; I _f = 0.27; and I _tot = 0.36 for rural Chuvashes, respectively; and I _m = 0.04; I _f = 0.30; and I _tot = 0.35 for urban, and I _m = 0.03; I _f = 0.29; and I _tot = 0.33 for rural Russians, respectively.__________Translated from Genetika, Vol. 41, No. 6, 2005, pp. 850–854.Original Russian Text Copyright © 2005 by El’chinova, Zinchenko, Kirillov, Abrukova.     

BIODIVERSITY RESEARCH: Turning up the heat: the impacts of Andropogon gayanus (gamba grass) invasion on fire behaviour in northern Australian savannas

Aim This study aimed to quantify changes in fire severity resulting from the invasion of Australia’s tropical savannas by the African grass Andropogon gayanus Kunth. (gamba grass). Location Mesic savannas of the Northern Territory, Australia. Method Byram’s fire‐line intensity (I_f), fuel load and architecture, and two post‐fire indicators of fire intensity – scorch height (SH) and char height (CH) of woody vegetation – were determined for fires in native grass savanna and A. gayanus invaded savanna. Leaf scorch is the height at which the fire’s radiant heat browns leaf tissue, and leaf char is the height that radiant heat blackens or consumes leaf tissue and provides an indirect measure of flame height. These data, and 5 years of similar data collected from the Kapalga Fire Project in Kakadu National Park, were used to develop empirical relationships between I_f and the post‐fire indices of fire intensity. Results A relationship between A. gayanus I_f and SH could not be developed because complete canopy scorch occurred in most A. gayanus fires, even at low I_f. In contrast, A. gayanus I_f was strongly correlated with CH. This empirical relationship was substantially different from that for native grass fires. For a given I_f, there was a significantly greater CH in invaded sites. This increase in radiant heat is attributable to the increased biomass (mean 3.6 t ha^?1 in native grasses compared to 11.6 t ha^?1 in A. gayanus) and height (approximately 0.5 m in native grasses compared to 4 m in A. gayanus) of the standing fine fuel. Main conclusion Andropogon gayanus invasion resulted in substantial changes in fire behaviour. This has important regional implications owing to the current (10,000–15,000 km²) and predicted (380,000 km²) area of invasion and the negative consequences for the native savanna biota that has evolved with frequent but relatively low‐intensity fire.     

The adaptive potential of a plant pathogenic fungus, <Emphasis Type="Italic">Rhizoctonia solani</Emphasis> AG-3, under heat and fungicide stress

The ability to improve fitness via adaptive evolution may be affected by environmental change. We tested this hypothesis in an in vitro experiment with the plant pathogen Rhizoctonia solani Anastomosis Group 3 (AG-3), assessing genetic and environmental variances under two temperatures (optimal and higher than optimal) and three fungicide concentrations (no fungicide, low and high concentration of a copper-based fungicide). We measured the mean daily growth rate, the coefficient of variation for genotypic (I _G) and environmental variance (I _E) in growth, and broad-sense heritability in growth. Both higher temperature and increased fungicide concentration caused a decline in growth, confirming their potential as stressors for the pathogen. All types of standardized variances in growth—I _G, phenotypic variance, and I _E as a trend—increased with elevated stress. However, heritability was not significantly higher under enhanced stress because the increase in I _G was counterbalanced by somewhat increased I _E. The results illustrate that predictions for adaptation under environmental stress may depend on the type of short-term evolvability measure. Because mycelial growth is linked to fitness, I _G reflects short-term evolvability better than heritability, and it indicates that the evolutionary potential of R. solani is positively affected by stress.     

A voltage-dependent and pH-sensitive proton current in Rana esculenta oocytes

Voltage clamp technique was used to study macroscopic ionic currents in Rana esculenta oocytes. Depolarization steps led to the activation of a single type of outward current (I _out) when contaminant potassium and calcium-dependent chloride currents were pharmacologically inhibited. The voltage threshold of I _out activation was 10 mV and this current, which did not inactivate, presented a deactivation the time constant of 73±21 msec (n=26) corresponding to a membrane voltage of –60 mV. Its reversal potential (E _rev) was dependent on the magnitude of the depolarization and also on pulse duration. These changes in E _rev were thought to reflect intracellular ion depletion occurring during activation of the remaining outward current. Furthermore, the activation threshold of I _out was clearly affected by modifications in extracellular and intracellular H⁺ concentrations. Indeed, intracellular alkalinization (evoked by external application of ammonium chloride) or extracellular acidification induced a rightward shift in the activation threshold while intracellular acidification (evoked by external application of sodium acetate) or extracellular alkalinization shifted this threshold toward a more negative value. Lastly, I _out was dramatically reduced by divalent cations such as Cd²⁺, Ni²⁺ or Zn²⁺ and was strongly decreased by 4 Aminopyridine (4-AP), wellknown H⁺ current antagonists already described in many cell types. Therefore, it was suggested that the outward current was prominently carried by H⁺ ions, which may play a key role in the regulation of intracellular pH and subsequent pH dependent processes in Rana oocyte.     

Epidemiological research of twig scab on pear as basis for a rational and ecological disease management

Scab is one of the key parasites in fruit growth. In favourable weather conditions for the pathogen, a complete harvest can be destroyed if no control measurements are undertaken. The scab fungi on pear and apple are two distinct species. They have, however, a similar biological cycle. Despite the similarities, there are also clear differences and these differences are significant for the control of the pathogen. Pear scab does not only infect fruit and leaves as apple scab does, but also infects twigs. Especially in organic fruit growing, twig scab is a big problem. Once twig scab occurs, it seems to be impossible to get rid of scab in these orchards. The only possibility for the fruit grower in this case is a strict spraying schedule to ensure no further spread of the infection. The main goal of the project is a thorough study of the pear scab fungi (biology, sensitivity of different plant parts and cultivars, dispersal of the fungi and infection conditions, the pathogenicity and characterization of different biotypes) to unravel the life of the fungi and to develop a better control strategy. A better control strategy means a reduced fungicide use and a reduction of fungicide residue on the fruits at harvest, without a reduction of the quality of the fruits and cost effectiveness for the fruit grower. Special attention in the project goes to the role and the control of twig scab. The first results of this project will be shown.     

Molecular configuration of amylose and its complexes in aqueous solutions. Part II. Relation between the DP of helical segments of the amylose–iodine complex and the equilibrium concentration of free iodine

The iodine which is added to an aqueous amylose solution is bound only partly by the amylose while forming the blue complex and partly remains free. The equilibrium normality of the free and the bound iodine at half-saturation of amylose by iodine is designated as [I_f]_v and [I_b]_w, respectively. The stability of the poly iodine chain formed within the axis of amylose helices depends on its length, i.e., indirectly on the DP of the amylose helices: the greater this stability, the lower the [I_f]_v value. The amylose molecule consists of helical segments. Such a molecule may behave as a random coil. The average length of the helical segments in freshly prepared amylose-iodine complexes depends on temperature, pH, iodide concentration, the presence of other complex-forming agents, and the DP of the amylose. This latter factor is investigated in the present paper. By the aid of an automatically recording photometrictitrating device the coherent values of [I_b] and [I_f] were determined. Plotting these values against DP _n for mechanochemically degraded as well as for periodateo-xidized amyloses resulted in curves consisting of two linear sections. The break of the curves occurred between DP _n 110 and 130. It was concluded that below DP _n = 100 the DP of helical segments (= sDP _n) is identical to the DP _n of the total molecule, i.e., the molecule consists of only a single, relatively stiff helix. Above this limit the molecule contains several helical segments. The DP of these helical segments can be calculated as follows: sDP _n = 141.1 ? 10.2 × 10⁵[I_f]_v. This equation is considered to be valid for 0.5–0.6 mg. amylose in 100 ml. 0.1N HCl at 20°C., λ = 650 mμ, euuvet diameter 3.4 cm., the feed rate of the iodate-iodide titrating solution (in acid medium resulting in a 5 × 10^?3N I₂ solution with a molar iodide to iodine ratio of 1.5) is 0.4ml./min. Amylose molecules of, e.g., DP ⁿ = 1380 consist of an average of 11.4 segments having a DP of about 120 and consisting of an average of 15–18 helical turns.     

Micronised and non-micronised sulphur applications control peach scab equally well with negligible differences in fruit quality

In a 2-year study, micronised (finely ground) and non-micronised sulphur spray programmes were investigated for peach scab control and influence on peach fruit quality variables including fruit colouration, soluble solids content and flesh firmness. Both sulphur programmes, applied six or 11 times at 15 kg ha⁻¹, controlled scab equally well in both years on cultivars (cvs) Contender and Cresthaven. Six applications of a half dosage of both micronised and non-micronised sulphur programmes were significantly less effective ( P  < 0.05) compared with all other programmes when scab incidence was >90% on cv. Contender. None of the sulphur programmes influenced significantly ( P  < 0.05) colouration and flesh firmness of harvested fruits compared with the industry standard (a chlorothalonil–captan programme). Only soluble solids concentrations showed significant differences among fungicide programmes ( P  < 0.05), but these differences were not consistent with either particle sizes of sulphur fungicide or reduced application fungicide programmes. In conclusion, our study showed that (a) micronised sulphur did not control peach scab more effectively compared to non-micronised sulphur; (b) six applications of sulphur were sufficient to control peach scab when disease pressure was low to medium; and (c) neither six nor 11 applications of sulphur-based products applied at 15 kg ha⁻¹ had commercially relevant negative impacts on important peach fruit quality variables.     

Effect of five fungicides with different modes of action on cobweb disease (Cladobotryum mycophilum) and mushroom yield

The fungicides chlorothalonil, metrafenone, prochloraz‐Mn, thiabendazole and thiophanate‐methyl were tested in vitro and in vivo for their effect on Cladobotryum mycophilum, the mycoparasite that causes cobweb disease in white button mushroom. In vitro experiments showed that metrafenone (EC₅₀= 0.025 mg L^?1) and prochloraz‐Mn (EC₅₀= 0.045 mg L^?1) were the most effective fungicides for inhibiting the mycelial growth of C. mycophilum. Selectivity indexes of the tested fungicides on both C. mycophilum and Agaricus bisporus indicated that metrafenone was also the most selective fungicide, while chlorothalonil was the most toxic fungicide against A. bisporus mycelium. The in vivo efficacy of fungicides for controlling cobweb was evaluated in three mushroom cropping trials, which were artificially inoculated with C. mycophilum (10⁶ conidia m^?2). Prochloraz‐Mn provided good control, although the surface colonised by cobweb reached 12% by the end of the crop cycles. None of the inoculated cropping trials treated with metrafenone showed any cobweb disease symptoms, and neither were any significant phytotoxic effects on mushroom yield recorded. These results indicated that metrafenone can be used as an alternative to prochloraz‐Mn in the control of cobweb disease.     

<Emphasis Type="Italic">Vr</Emphasis><Subscript><Emphasis Type="Italic">2</Emphasis></Subscript>: a new apple scab resistance gene

Reports from several European countries of the breakdown of the Vf resistance, the most frequently used source of resistance in breeding programs against apple scab, emphasize the urgency of diversifying the basis of apple scab resistance and pyramiding different apple scab resistances with the use of their associated molecular markers. GMAL 2473 is an apple scab resistant selection thought to carry the resistance gene Vr. We report the identification by BSA of three AFLP markers and one RAPD marker associated with the GMAL 2473 resistance gene. SSRs associated with the resistance gene were found by (1) identifying the linkage group carrying the apple scab resistance and (2) testing the SSRs previously mapped in the same region. One such SSR, CH02c02a, mapped on linkage group 2, co-segregates with the resistance gene. GMAL 2473 was tested with molecular markers associated with other apple scab resistance genes, and accessions carrying known apple scab resistance genes were tested with the SSR linked to the resistance gene found in GMAL 2473. The results indicate that GMAL 2473 does not carry Vr, and that a new apple scab resistance gene, named Vr ₂, has been identified.     

Integrating cultural control methods for tomato late blight (Phytophthora infestans) in Uganda

Cultural control measures against tomato late blight (Phytophthora infestans) were evaluated in six field experiments over 3 years in Uganda. Each experiment included sanitation (removal of diseased plant tissues), fungicide (mancozeb) application, and an untreated control, as standard treatments. Late blight incidence and severity were greatly reduced by sanitation, without reducing the number of healthy leaves; however, tomato growth and production were adversely affected. Fungicide treated plants retained the highest numbers of flowers and attached fruits and gave the highest yields. Three cultural practices were evaluated in repeated experiments for their effectiveness in alleviating the adverse effects of sanitation. Tomatoes grown within plastic shelters early in the production cycle were taller, and had more healthy leaves than those grown late. The numbers of diseased leaves and disease severity were equally low in sanitation alone and plastic shelter/with sanitation treatments. Flower and fruit production were significantly higher when tomatoes were grown under early shelters with sanitation than with sanitation alone. Planting density was increased without significant effects on late blight and tomato growth and production. Intercropping tomato with soybean (Glycine max) or sesame (Sesamum indicum), with sanitation, limited late blight development, but taller intercrops suppressed tomato growth and production. Integrated treatments (combining plastic shelters, a sesame intercrop and high tomato planting density) were evaluated, with and without sanitation, against the fungicide mancozeb. The mean numbers of healthy leaves in the integrated treatments were not significantly less than with fungicide treatment. Late blight incidence and severity were higher in the integrated plots without than with sanitation. The numbers of flowers and attached fruits were not significantly less in integrated treatments than in fungicide treated plots, but tomato yield was highest with fungicide treatment.