Comparison of fungicides for control of leaf spot (Septoria apiicola) of celery

Of twenty-one fungicides tested at recommended rates of application for their effectiveness in controlling leaf spot of celery grown in Ireland on peat and on a clay-loam soil, three formulations containing fentin acetate with maneb and formulations of fentin hydroxide and fentin chloride were most effective. Benomyl was superior to the other non-tin fungicides tested and, at moderate disease levels, it resulted in marketable yields of celery equal to those recorded after treatment with the organotin compounds. Generally, the organotin compounds and benomyl were followed in descending order of effectiveness by copper oxychloride, captafol, Daconil 2787 and maneb. None of the fungicides tested in the three seasons caused visible symptoms of phytotoxicity and, on disease-free celery in 1969, none had a significant effect on yield.     

Methods of assessment celery leaf spot (Septoria apiicola) in relation to fungicide evaluation

Six criteria for evaluating fungicides for control of celery leaf spot (Septoria apiicola) were compared. Two of these criteria consisted of yield measurements, of which marketable yield gave better statistical separation of the fungicides than gross yield. Of the other four criteria, assessment of leaf spot on a whole-plot basis was the most valuable. Overall disease rating on individual intact plants, rating of each petiole and numbers of diseased petioles per plant were less useful assessment criteria.     

Control of dark leaf spot (Alternaria brassicicola) of Brassica oleracea seed production crops with foliar sprays of iprodione

Three sprays of iprodione (Rovral 50% w. p.) at 0.5-1 kg a. i./ha applied to Brassica oleracea seed crops in experimental plots and field trials at 3-wk intervals from the young green pod stage until cutting controlled pod infection caused by A. brassicicola in seasons 1976–1979. As a result few seeds were infected, seed yields were increased and their germination was improved. Sprays of Bordeaux mixture were as effective as iprodione in years when disease levels were low but were ineffective when infection pressure was severe.     

Studies on watercress chlorotic leaf spot virus and on the control of the fungus vector (Spongospora subterranea) with zinc

Watercress chlorotic leaf spot virus (WCLV) caused a yellow leaf spot disease of watercress at Pickering, Yorkshire. The virus was mechanically transmitted to and maintained in Chenopodium quinoa, C. amaranticolor and Petunia hybrida in which it caused systemic symptoms. It could not be mechanically transmitted, however, from infected C. quinoa to Chrysanthemum, Gynura aurantia, potato, tomato, watercress or nine other species of Cruciferae. WCLV could be partially-purified after extraction in weak (0.05–0.1 M) but not strong (0.5 M) phosphate or tris/HCl buffer after clarification with diethyl ether and acidification to pH 3.9–4.0. Preparations were non-infective if treated with 5% (vlv) ethanol or n-butanol or if stored at — 12°C for 1 day or heated for 10 min at 54°C. Preparations were non-infective after treatment with RNase or proteinase K but not after treatment with DNase. The virus was present in roots of diseased watercress plants which also contained the watercress crook root disease fungus Spongospora subterranea f. sp. nasturtii. Tests showed that WCLV was transmitted by S. subterranea zoospores and that it persisted in the resting spores of the fungus. The crook root disease was controlled by adding 0.3–0.5 μg Zn/ml to the inlet water supply to the crop. The water that had flowed through the crop contained 0.05–0.10 μg Zn/ml. Although this increased the zinc content of the watercress from 8–9 in untreated beds to 16–48 μg Zn/g in treated beds, this was below the tolerance recommended by the Food Standards Committee. A method is described of obtaining accurate dilutions of solutions of zinc sulphate (20% w/v ZnSO₄.H₂O) in the water supplying the crop using solutions of the red dye Ariavit Amaranth.     

Effectiveness and residues of procymidone applied on celery and fennel in the control of Sclerotinia sclerotiorum (Lib.) de Bary

A biennial experimentation has been led using the active ingredient (a.i.) procymidone, for the control of Sclerotinia sclerotiorum (Lib.) De Bary on fennel and celery. At present this utilizathion it is not authorized, even though this "minor use" is considered essential for the control of the various phytopathologies. For every test, both in field and in greenhouse, two treatments to the dose of 40 g/hl of a.i. have been made. After the second treatment two assessments were led to check effectiveness of a.i. and subsequent vegetable samplings have been made to determine the entity and the persistence of the residues of the used active ingredient. At the end of the agricultural cycle, in all the tests a good control of the infection caused by the fungus has been found; statistically significant differences of the infection between treated plots and the control. At harvesting (21 days from the 2nd treatment) we have found a residue average value of 0.1-0.2 mg/kg (field) and 0.3-0.4 mg/kg (greenhouse) on fennel and of: 1.0-1.5 mg/kg (field) e 3.0-3.5 mg/kg (greenhouse) on celery.     

A bacterial leaf spot of Protea cynaroides (king protea)

The etiology of a new leaf spot disease on king protea was investigated. The causal organism was a Gram negative rod-shaped bacterium with between two and seven flagella. On the basis of cultural, biochemical and physiological characters it was identified as a pathovar of Pseudomonas syringae.     

Concentric leaf spot of yam (Dioscorea spp) in South-western Nigeria

The etiology and epidemiology of concentric leaf spot and seedling blight diseases of yam (Dioscorea spp) was investigated at Jbadan, south western Nigeria, in the low land humid tropics. Sclerotium rolfsii was associated with the concentric leaf spot and seedling blight of yam. The pathogen was also harbored by weeds namely Mucuna pruriensis, Commelina erecta, ipomea triloba, I. involucrataand Ipomoea sp found growing within the yam plots. A high mean inoculum densities of 3.0 ± 0.5 × 10⁶ colony forming unit/g of soil was estimated in the soil samples obtained from the yam plots This revised version was published online in June 2006 with corrections to the Cover Date.     

Genetic mapping of gray leaf spot (GLS) resistance genes in maize

Bulked segregant analysis was used to identify amplified fragment length polymorphism markers (AFLPs) linked to quantitative trait loci (QTLs) involved in the resistance to gray leaf spot (GLS) in maize. By using ten AFLP primer combinations 11 polymorphic markers were identified and converted to sequence- specific PCR markers. Five of the 11 converted AFLPs were linked to three GLS resistance QTLs. The markers were mapped to maize chromosomes 1, 3 and 5 using existing linkage maps of two commercially available recombinant inbred-line populations. Converted restriction fragment length polymorphism markers and microsatellite markers were used to obtain a more-precise localization for the detected QTLs. The QTL on chromosome 1 was localized in bin 1.05/06 and had a LOD score of 21. A variance of 37% was explained by the QTL. Two peaks were visible on chromosome 5, one was localized in bin 5.03/04 and the other in bin 5.05/06. Both peaks had a LOD score of 5, and 11% of the variance was explained by the QTLs. A variance of 8–10% was explained by the QTL on chromosome 3 (bin 3.04). The consistency of the QTLs was tested across two F₂ populations planted in consecutive years. Received: 10.10.00 / Accepted: 26.01.01     

Effects of inoculum concentration, leaf age and wetness period on the development of dark leaf and pod spot (Alternaria brassicae) on oilseed rape (Brassica napus)

Experiments were done under controlled environment and glasshouse conditions to study the effects of inoculum concentration, leaf age and wetness period on the development of dark leaf and pod spot (Alternaria brussicae) on oilseed rape (Brassica napus). On leaves of potted oilseed rape plants (cv. Bienvenu) inoculated with A. brassicae conidial suspensions, the severity (number of lesions cm^-2) of dark leaf spot increased as inoculum concentration increased from 80 to 660 spores ml^-1and as leaf age increased from 4 to 14 days. On pods on detached racemes of spring oilseed rape (cv. Starlight), the incidence of dark pod spot (% of pods diseased) increased as inoculum concentration increased from 80 to 10⁴spores ml^-1. Increasing inoculum concentration above 10⁴spores ml^-1did not increase the incidence but did increase the severity of dark pod spot. A minimum wetness period of 4 h was needed for infection of oilseed rape leaves (cv. Envol) by A. brussicue at 18°C and disease severity increased with increasing wetness period up to 12 h. The length of dry interruptions after 3–8 h of initial wetness affected the severity of dark leaf spot. A second wetness period increased the severity of dark leaf spot if the dry interruption was ≤ 6 h and if the first wetness period was ≤ 8 h. The incubation period of A. brassicae decreased from 3.5 to 2.5 days as inoculum concentration increased from 80 to 660 spores ml^-on leaves (cv. Bienvenu) at 17–25°C and from 3.8 to 1.0 day as inoculum concentration increased from 80 to ≥2 ≥ 10³spores ml^-1on pods (cv. Starlight) at 18°C.     

Diagnosis of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) in the UK

Light leaf spot lesions were generally first observed as light green areas on leaves of UK winter oilseed rape crops in January or February and later became brittle and bleached. Elongated lesions, which were brown with indistinct edges, developed on stems in the spring and summer, when lesions were also observed on flower buds, pedicels and pods. Development of diagnostic white pustules (spore masses of Pyrenopeziza brassicae, which erupt through surfaces of infected tissues) for confirmation of light leaf spot infection on symptomless plants or plants with indistinct or ambiguous symptoms in the autumn, winter or spring was enhanced by incubating plants in polyethylene bags. In experiments with artificially inoculated plants, glasshouse-grown plants exposed in infected crops and plants sampled from crops, white pustules developed at all incubation temperatures from 2^oC to 20^oC on infected leaves of different cultivars. The period of incubation required before the appearance of pustules decreased as the time that had already elapsed since the initial infection increased. The longest periods of incubation were required at the lowest temperatures (2^oC or 5^oC) but leaves senesced and abscised from plants most quickly at the highest temperatures (15^oC or 20^oC), suggesting that the optimal incubation temperature was between 10^oC and 15^oC.     

Effect of copper hydroxide sprays for citrus canker control on wild-type Escherichia coli

Aims: To show that application of copper hydroxide citrus sprays mixed with field source water (possibly contaminated) will not support Escherichia coli on plant surfaces. Environmental stresses of transient phyllosphere bacteria and presence of copper will eradicate these bacteria before harvest. Methods and Results: Studies were performed in vitro with bacteria grown in broth and then subjected to field spray copper hydroxide concentrations in the broth and on citrus leaves. Escherichia coli exposed to copper hydroxide in vitro were eradicated from the broth within 6–8 h depending on the broth pH. Even with near neutral pH (7·2), cells began to die immediately after exposure to copper. No E. coli survived on leaf surfaces sprayed with copper. Conclusions: Copper field sprays mixed with water that may contain E. coli can help eliminate E. coli from plant surfaces. Significance and Impact of the Study: HACCP mandates are becoming more restrictive because of the increased illness resulting from food pathogens on fresh produce. Use of potable water in fields, a proposed mandate, is not feasible for large grove owners. These data show that copper sprays aimed at reducing citrus canker also affect E. coli and may help to ease water quality mandates.     

Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) chemical control: residues associated with the three consecutive spray strategy

Abstract  Chemical control of western flower thrips Frankliniella occidentalis requires three consecutive applications of the same pesticide, 3–6 days apart. Initially, pesticides recommended for western flower thrips control were based on established maximum residue limits (MRLs) from previously established use on pests other than F. occidentalis , rather than product efficacy against F. occidentalis . Moreover, MRLs were based on a single application rather than three consecutive sprays. Chemical residues associated with the three-spray strategy were not quantified. Here those residues are quantified and the scope for rate increases is further tested, as laboratory bioassays suggest that some current permit rates may be too low to be effective. At established withholding periods (WHPs), current permit rate applications of abamectin (0.018 g/L) on strawberry and tomato, and methidathion (0.5 g/L) and endosulfan (0.666 g/L) on lettuce produced residues above the current Australian MRL. Results indicated that a higher than the current permit rate for endosulfan (2.0 g/L) could be sustained on cucumber and strawberry at established WHPs, but would require an extension to the current WHP. Similarly, a modest increase in methidathion (1.0 g/L) rate on tomato could be practical, again with a WHP extension. In each instance additional supporting data are required to accurately quantify the proposed WHP extensions.     

Analysis and modelling of effects of leaf rust and Septoria tritici blotch on wheat growth

A model to predict Septoria tritici blotch (STB) and leaf rust effects on wheat growth was constructed and evaluated in two steps. At the leaf scale, Bastiaans' approach that predicts the relative photosynthesis of a wheat leaf infected with a single disease, was extended to the case of two diseases, one biotrophic and one necrotrophic by considering the leaf rust-STB complex. A glasshouse experiment with flag leaves inoculated either singly with one disease or with two diseases combined was performed to check the leaf damage model. No interaction of the two diseases on photosynthesis loss was observed when they occurred simultaneously on the same leaf. In a second step, the single-leaf model was extended to the canopy scale to model the effects of the leaf rust-STB complex on the growth of a wheat crop. The model predicts the effects of disease on the growth of an affected crop relative to the growth of a healthy crop. The canopy model accounted for different contributions to photosynthetic activity of leaf layers, derived from their position in the canopy and their natural leaf senescence. Treatments differing in nitrogen fertilization, microclimatic conditions, and wheat cultivars were implemented in a field experiment to evaluate the model. The model accurately estimated the effect of disease on crop growth for each cultivar, with differences from experimental values lower than 10%, which suggests that this model is well suited to aid an understanding of disease effects on plant growth. A reduction in green leaf area was the main effect of disease in these field experiments and STB accounted for more than 70% of the reduction in plant growth. Simulations suggested that the production of rust spores may result in a loss of biomass from diseased crops and that stem photosynthesis may need to be considered in modelling diseased crop growth.     

The effect of Trichoderma harzianum and T. koningii on the control of tan spot (Pyrenophora tritici-repentis) and leaf blotch (Mycosphaerella graminicola) of wheat under field conditions in Argentina

The effect of six isolates of Trichoderma harzianum and one isolate of T. koningii on the incidence and severity of tan spot (Pyrenophora tritici-repentis) and leaf blotch of wheat (Mycosphaerella graminicola) was evaluated under field conditions. Significant differences between wheat cultivars, inoculum types and growth stages were found. Three of the isolates tested (T2 for M. graminicola, T7 for P. tritici-repentis and T5 for both of them) showed the best performance in controlling leaf blotch and tan spot when coated onto seed or sprayed onto wheat leaves at different growth stages, with significant severity reduction up to 56%. At tillering, six of the isolates reduced the severity of P. tritici-repentis and M. graminicola compared to the control by up to 39% and 12-53%, respectively. In some experiments, the biocontrol preparation (T2 and T5) gave a level of disease control similar to that obtained with Tebuconazole (70 and 48%, respectively). The effect of Trichoderma against P. tritici-repentis was also observed at the heading stage, when six of the treatments reduced disease severity by 16-35%. This is the first report on the efficacy of Trichoderma spp. against wheat necrotrophic pathogens under field conditions in Argentina.     

Methods for assessment of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) in the UK

Light leaf spot (Pyrenopeziza brassicae) was assessed as % plants with light leaf spot, % leaves with light leaf spot or % leaf area with light leaf spot in winter oilseed rape field experiments done at different sites (Rothamsted, Hertfordshire; Boxworth, Cambridgeshire; near Aberdeen, Scotland), with different cultivars (e.g. Bristol and Capitol), different fungicide treatments, on plants sampled at different dates. Regression analyses on data from these experiments showed that there were consistently good relationships between % leaves with light leaf spot and % plants with light leaf spot for plants sampled during the autumn and winter, until the % plants with light leaf spot approached 100%. The slopes and positions of regression lines were sometimes affected by cultivar, fungicide treatment or sampling date, but not by site. The relationship between % leaf area with light leaf spot (square root-transformed) and % leaves with light leaf spot was less consistent than that between % leaves with light leaf spot and % plants with light leaf spot and was sometimes affected by cultivar, fungicide treatment or sampling date but not by site. The relationship between % leaf area with light leaf spot (square root-transformed) and % plants with light leaf spot was also inconsistent and was sometimes affected by cultivar, fungicide treatment, sampling date and site.     

叶面积指数的研究和应用进展

对叶面积指数(LAI)提出50多年来,在植物光合作用、蒸腾作用、联系光合和蒸腾的关系和构成生产力基础的研究,在林分、景观以及地区尺度上对碳、能量、水分通量的研究,借助遥感技术建立森林生态系统的生长模型以及研究森林生态系统的能量和水分交换等方面的研究和应用进展进行了综述。LAI作为进行植物群体和群落生长分析的一个重要参数,已在农业、果树业、林业以及生物学、生态学等领域得到广泛应用。