Efficacy of 1,3-dichloropropene plus chloropicrin application methods in combination with pebulate and napropamide in tomato

Small-plot research and large-field validations were conducted to determine the effect of 1,3-dichloropropene (1,3-D)+chloropicrin (Pic) application methods in combination with the herbicides pebulate and napropamide on pest control in fresh market tomato (Lycopersicon esculentum Mill.). In both the small-plot trials and the large-validation fields, various treatments compared the efficacy of soil fumigants and herbicides based on methyl bromide, in-bed and broadcast applications of 1,3-D+Pic, pebulate, and napropamide. The results consistently indicated that either in-bed or broadcast applications of 1,3-D+Pic in combination with pebulate and napropamide are equally effective against the weed Cyperus spp., the nematodes Tylenchorhynchus spp., Belonolaimus longicaudatus, and Meloidogyne spp., and the soilborne disease Fusarium oxysporum f.sp. lycopersici in fresh market tomato. Therefore, broadcast 1,3-D+Pic application can reduce personnel exposure and poisoning risks, without losing pest control efficacy.     

Effects of 1,3-dichloropropene on nematode,weed seed viability and soil-borne pathogen

1,3-dichloropropene (1,3-D, C₃H₄Cl₂) is one of the potential candidates as soil disinfectant since the restriction of methyl bromide (MeBr) in soil fumigation due to its ecological risk. Its nematode, soil-borne pathogen and weed control efficacies were evaluated in a laboratory dose-response study and in two commercial tomato fields. Laboratory studies found that the seeds of Digitaria chinensis Hornem. were the most sensitive to soil fumigation with 1,3-D, followed by Eleusina indica (Linn.) Gaertn., Echinochloa crusgalli (L.) Beauv. and Amaranthus retroflexus L. with the LC₉₀ values between 14.23 and 73.59 mg kg⁻¹ soil. Among the pathogens, Phytophthora capsici Leonian was the most sensitive and Fusarium oxysporum f. sp. fragariae was the least sensitive to 1,3-D fumigation with the LC₅₀ values were 0.24 and 1.55 g m⁻². Rhizoctonia solani Kühn., Phytophthora nicotianae var. nicotianae and Botrytis cinerea Persoon exhibited intermediate susceptibility. Field trials revealed that 1,3-D applied to the field at 180, 120 and 80 L ha⁻¹ could suppress Meloidogyne incognita root galling while maintaining high tomato marketable yields, better than Dazomet at the concentration of 400 kg ha⁻¹. Our results indicated that 1,3-D was an excellent nematicide and could provide good to moderate weed and pathogen control. Based on our results, 1,3-D, in combination with other alternatives to MeBr is recommended to reach an integrated pest management.     

Effects of the nematicide 1,3-dichloropropene on weed populations and stem canker disease severity in potatoes

The soil fumigant 1,3-dichloropropene (1,3-D) has been used in the UK for the control of potato cyst nematodes (PCN), Globodera pallida (Stone) and Globodera rostochiensis (Wollenweber), but its potential herbicidal activity has not been extensively investigated in this country. Field and glasshouse studies were therefore conducted to evaluate the potential of 1,3-D for the control of weeds in potatoes, and observations were made on the severity of potato stem canker, caused by the fungus Rhizoctonia solani Kühn [teleomorph: Thanatephorus cucumeris (Frank) Donk]. Autumn application of 1,3-D at 211.5 L active substance (a.s.) ha⁻¹ significantly suppressed the number of germinating weeds and the percentage of weed ground cover by 83% and 79%, respectively, relative to controls. There were also species-specific significant decreases (field pansy, Viola arvensis, in particular) in the number of weed seeds germinating in field soil in the glasshouse post-1,3-D treatment. The effect of 1,3-D declined in time and single (autumn or spring) or combined application produced a slight, but not significant, reduction in the number of weeds germinated on potato ridges relative to those recorded in untreated soil. The severity of stem canker on potato plants was not significantly reduced by 1,3-D but both mean number and weight of stems per plant were significantly increased compared with plants from untreated plots. These studies demonstrated that 1,3-D, in addition to giving PCN control, has efficacy against weeds; implications are the potential for reduced herbicide input in the crop rotation with accompanying economic and environmental benefits.     

Effects of soil amendment with poultry manure on carnation Fusarium wilt in greenhouses in southwest Spain

In a search for alternatives to methyl bromide for controlling carnation vascular wilt caused by Fusarium oxysporum f. sp. dianthi (Fod), poultry manure plus soil solarization was studied in soil under greenhouse conditions in four 2-year experiments. These were conducted in naturally infested soil to compare the effects of this treatment with soil solarization alone and methyl bromide. Soil treatments were performed during June 2000 for Experiment 1, from July to mid-August 2002 for Experiment 2, from late July to late August 2006 for Experiment 3 and from late May to late June 2008 for Experiment 4. Additionally, a treatment with commercial poultry manure pellet plus soil solarization was included in the two latter experiments. Poultry manure caused reductions of Fod viability in soil samples at depths of 15 and 30 cm, ranging respectively from 93 to 100% and 89 to 100% for Experiments 1, 2 and 3. Carnations planted in plots treated either with poultry manure, methyl bromide or soil solarization had lower final disease incidences, smaller areas under their disease progress curves and higher yields in comparison with untreated plots in Experiments 2, 3 and 4. In Experiment 1, soil solarization was performed under suboptimal conditions, and it provided disease levels and yields similar to those of the untreated control plots. Nevertheless, under the same conditions, previous amendment of Fod-infested soil with poultry manure increased disease control over soil solarization alone, improved carnation yield and quality and also increased plant vigor, thus providing a satisfactory alternative to methyl bromide. The application of organic amendment to the same plot before every crop cycle is recommended to ensure continuous disease control, but the rates of application could be reduced to half for the third and fourth crop cycles, thereby reducing undesirable environmental effects.     

Evaluation of actinomycete isolates obtained from herbal vermicompost for the biological control of Fusarium wilt of chickpea

A total of 137 actinomycetes cultures, isolated from 25 different herbal vermicomposts, were characterized for their antagonistic potential against Fusarium oxysporum f. sp. ciceri (FOC) by dual-culture assay. Of the isolates, five most promising FOC antagonistic isolates (CAI-24, CAI-121, CAI-127, KAI-32 and KAI-90) were characterized for the production of siderophore, cellulase, protease, hydrocyanic acid (HCN), indole acetic acid (IAA) and antagonistic potential against Rhizoctonia bataticola, which causes dry root rot in chickpea (three strains viz. RB-6, RB-24 and RB-115) and sorghum (one strain). All of the five FOC antagonistic isolates produced siderophore and HCN, four of them (except KAI-90) produced IAA, KAI-32 and KAI-90 produced cellulase and CAI-24 and CAI-127 produced protease. In the dual-culture assay, three of the isolates, CAI-24, KAI-32 and KAI-90, also inhibited all three strains of R. bataticola in chickpea, while two of them (KAI-32 and KAI-90) inhibited the tested strain in sorghum. When the FOC antagonistic isolates were evaluated further for their antagonistic potential in the greenhouse and wilt-sick field conditions on chickpea, 45-76% and 4-19% reduction of disease incidence were observed, respectively compared to the control. The sequences of 16S rDNA gene of the isolates CAI-24, CAI-121, CAI-127, KAI-32 and KAI-90 were matched with Streptomyces tsusimaensis, Streptomyces caviscabies, Streptomyces setonii, Streptomyces africanus and an identified species of Streptomyces, respectively using the BLAST searching. This study indicated that the selected actinomycete isolates have the potential for biological control of Fusarium wilt disease in chickpea.     

Effects of agrochemical treatments on the occurrence of Fusarium ear rot and fumonisin contamination of maize in Southern Italy

The efficacy of agrochemical treatments, based on three different fungicides combined with an insecticide, was tested in southern Italy for two years on three maize hybrids to control Fusarium ear rot of maize and the accumulation in the maize kernels of the carcinogenic mycotoxins fumonisins. Insect damage incidence and severity, disease incidence and severity, identification of Fusarium species and levels of fumonisin contamination in kernels were determined. Field trials showed in both years that natural colonization of maize kernels by the fumonisin producing species Fusarium proliferatum and F. verticillioides (up to 81.5 and 26.5%, respectively) and total fumonisin contamination (up to 68.2 μg g⁻¹) were highly severe. For all hybrids and in both years, the treatment with the insecticide applied alone reduced the insect damage severity consistently and the content of fumonisins in the kernel only in half of the cases, whereas fungicide treatments applied in combination with the insecticide showed a further significant reduction of fumonisin contamination in the three hybrids and in both years.     

A disease survey of Fusarium wilt and Alternaria blight on sweet potato in South Africa

A disease survey was conducted on sweet potato in the major production areas of South Africa in 2006-2008 to determine the importance of wilt disease (WD) and Alternaria blight (AB) caused by Alternaria bataticola. The disease prevalence, incidence and severity were assessed for both WD and AB in 58 sweet potato fields in seven provinces, and included both commercial and resource-poor growers. The prevalence of WD in commercial fields was significantly higher than in resource-poor fields; while disease incidence and severity were very low in both commercial and resource-poor fields. Soil pH showed a moderate negative linear correlation to WD severity. WD is at present considered a minor disease of sweet potato in South Africa, although local outbreaks can be damaging. AB had very low disease prevalence, incidence and severity levels in both commercial and resource-poor fields countrywide. However, one of the fields had moderately high disease incidence and severity levels, showing that the disease can be destructive if not controlled. AB should be considered a potentially destructive disease of sweet potato in South Africa. Fusarium oxysporum was consistently isolated from WD plants, with F. oxysporum f. sp. batatas identified, but other formae speciales were also associated with the disease.     

Effects of fungicide seed treatments on germination, population, and yield of maize grown from seed infected with fungal pathogens

Seedborne fungi can reduce survival, growth, and yield of maize (Zea mays L.). Laboratory, field, and growth chamber experiments were conducted to determine the effects of the seed treatment fungicides fludioxonil, mefenoxam, and azoxystrobin on germination, plant population, and grain yield of maize grown from low-quality hybrid seed infected with seedborne fungal pathogens. Study I used seed of four hybrids infected at 0-54% incidence with Fusarium spp., Stenocarpella maydis, Penicillium spp., Rhizopus spp., and/or Aspergillus spp. Study II used three seed lots for each of two hybrids infected at 7-37% incidence with S. maydis. Warm and cold germination for untreated seed varied among hybrids in both studies. Warm germination of the seed lot with the highest incidence of S. maydis in study II treated with azoxystrobin and fludioxonil was significantly greater (+7%) than the nontreated control. Plant population in study I was significantly affected by seed treatment, hybrid, and their interactions. Populations were greater (≥9%) for fludioxonil, fludioxonil + mefenoxam, and fludioxonil + mefenoxam + azoxystrobin treatments compared to controls. In growth chamber experiments with pasteurized soil, emergence (≥5%) and plant dry weight (≥14%) were both greater than controls only with the triple seed treatment. Plant populations in study II for all seed treatments except mefenoxam and azoxystrobin alone were greater (≥4%) than controls. Yield in study I was significantly affected by hybrid and seed treatment. Yield for one hybrid was higher (≥20%) than the control with all seed treatments except fludioxonil, whereas yield with another hybrid was consistently greater (≥26%) only with the triple seed treatment. Yield in study II was significantly affected by hybrid, seed treatment, and their interactions. Yield was greater (≥8%) than the controls for all seed treatments with one hybrid and with all (≥5%) except azoxystrobin for the other hybrid. Highest yields occurred with the triple seed treatment. Results indicate that fludioxonil and azoxystrobin can increase germination, population, and yield of maize grown from seed infected by S. maydis and other fungi.     

Effects of crop rotation of soybean with corn on severity of sudden death syndrome and population densities of Heterodera glycines in naturally infested soil

Sudden death syndrome, caused by Fusarium virguliforme, and the soybean cyst nematode, Heterodera glycines, combined cause the highest yield losses in soybean. The objective of this study was to determine the effectiveness of corn rotated annually with soybean on reducing severity of sudden death syndrome (SDS) and if such crop rotation is beneficial to soybean root health and thus improves disease management strategies. Experiments were conducted from 2003 to 2006 through two cycles of a corn–soybean rotation on two commercial fields in Indiana. With one exception, the rotation of soybean with corn did not provide yield benefits compared to monoculture of soybean. Severity of foliar and root symptoms of SDS in rotation plots were never less than in soybean monoculture plots. At one location, soybean monoculture resulted in suppression of SDS compared to the corn–soybean rotation, while H. glycines reproduced freely. At the other location, monoculture of soybean resulted in suppressiveness against H. glycines, while SDS was limited in all treatments. The data suggest that soil suppressiveness can independently impact the pathogens that are important in SDS development. Because H. glycines can increase SDS symptoms, its suppression may also reduce severity of SDS. Current production systems consisting of yearly rotation of soybean with corn are highly vulnerable to the development of severe soil-borne disease complexes. The simple year-to-year rotation of corn and soybean is not considered sustainable. While monoculture of soybean resulted in some disease suppression in these trials, reliance on monoculture may be detrimental due to other environmental considerations beyond the scope of these trials. Including other crops may be beneficial in improving the sustainability of soybean and corn production systems.     

Management of fusarium basal rot (Fusarium oxysporum f. sp. cepae) on shallot through fungicidal bulb treatment

Fusarium basal rot caused by Fusarium oxysporum f.sp. cepae is an economic disease of shallot. Field experiments were conducted at Debre Zeit during 2006 and 2007 cropping seasons to determine effective fungicides and their method of application for the management of fusarium basal rot of shallot. The field was naturally infested with F. oxysporum f. sp. cepae and treatments were arranged in randomized complete block design in four replications. Five fungicides, Mirage 50 WP, Folicur 25 EC, Seed plus 30 WS, Penncozeb 80 WP and Ridomil Gold 68 WG were evaluated as seed bulb dressing and bulb dip treatments against basal rot in the field and storage. Bulb dressing with Mirage, and dip treatment in Seed plus reduced the disease incidence by 40% and 43%, respectively over control. These fungicides also resulted in a significant reduction in severity, basal rot affected cull bulbs on shallot. Bulb rot during three months of storage on concrete ground floor and on wire mesh shelves was also reduced by seed bulb treatment over control. The highest increase in yield was obtained from bulb dressing with Mirage (42%) and Seed plus (45%) and from bulb dip treatment in Seed plus (44%) over control. Fusarium basal rot caused 45% loss in yield and 12-30% of bulb loss in the storage. The study showed that basal rot of shallot can be managed effectively by seed bulb dressing or dip treatment in Mirage or Seed plus.     

Effect of plant growth promoting rhizobia on seed germination, growth promotion and suppression of Fusarium wilt of fenugreek (Trigonella foenum-graecum L.)

Five bacterial strains (TR1 to TR5) isolated from root nodules of fenugreek (Trigonella foenum-graecum) were tested for their plant growth promotory traits and biocontrol potential against Fusarium oxysporum. On the basis of morphological, physiological, biochemical and molecular characteristics, strains TR1 and TR3 - TR5 were identified as Ensifer meliloti, and TR2 as Rhizobium leguminosarum. All bacterial isolates utilized phosphate in vitro. Except TR5, all isolates produced IAA and none of them showed volatile cyanogens production. Except TR3, all isolates produced in vitro siderophore. Isolate TR1 and TR4 showed chitinase production while only TR2 showed β-1,3-glucanase activity. Isolates TR1, TR2 and TR5 exhibited ACC deaminase activity. Isolates TR1, TR2 and TR4 inhibited the growth of F. oxysporum, causing loss of structural integrity of the mycelium, hyphal perforation, lysis, fragmentation and degradation. The potential for nodulation and nitrogen fixation of the strains were confirmed by amplification of 500 bp nodC and 781 bp nifH fragments. The application of the TR1 + TR2 combination resulted in increased grain yield by 35% and 36% of fenugreek in two consecutive field trials, respectively as compared to control. Maximum increments in vigour index, nodule number and root and shoot biomass were recorded with seed inoculated with consortium (TR1 + TR2) followed by single inoculation as compared to control. The antibiotic resistant marker strain of E. meliloti TR1^strep+ and R. leguminosarum TR2^tet+ confirmed the efficient colonization of fenugreek roots. This study showed that these rhizobial isolates have properties of biocontrol agents and may be applied to promote the growth of fenugreek.     

Effectiveness of plant extracts on suppression of damping-off and wilt diseases of lupine (Lupinus termis Forsik)

The aim of this study was to evaluate water and organic solvent of plant extracts for protection of lupine plants against damping-off and wilt diseases caused by Fusarium oxysporum f. sp. lupini, F. oxysporum f. sp. lupini Snyder & Hansen was isolated from diseased lupine roots collected from different locations of Minia, Assiut and New Valley governorates. Water leaf extracts of Calotropis procera, Nerium oleander, Eugenia jambolana, Citrullus colocynthis, Ambrosia maritime, Acacia nilotica and Ocimum basilicum and fruit extracts of C. colocynthis, C. procera and E. jambolana reduced damping-off and wilt diseases caused by F. oxysporum f. sp. lupini. Water extracts of E. jambolana leaves, C. colocynthis fruits and N. oleander leaves were the most effective ones for controlling such diseases. In contrast, A. nilotica and O. basilicum extracts were the least effective ones. Organic solvent extracts of tested plants reduced damping-off and wilt diseases than water extracts. Butanolic and ethereal extracts were highly effective in reduction of diseases than the other tested extracts. Under field conditions, during winter growing seasons 2008/09 and 2009/10, ethereal and butanolic extracts of N. oleander and E. jambolana leaves and C. colocynthis fruits significantly reduced the percentage of wilt severity as well as improved growth parameters (plant height, number of branches, pods and seeds per plant) and increased seed index, total seed yield/hectare compared with control treatment, while protein content in seeds was not effected. In conclusion, our study demonstrated that some plant extracts can be used for biocontrol of lupine damping-off and wilt diseases.     

Effects of leaf scales of different pineapple cultivars on the epiphytic stage of Fusarium guttiforme

The fungus Fusarium guttiforme (Syn. F. subglutinans f. sp. ananas) is responsible for fusariosis, one of the main phytosanitary threats to pineapple (Ananas comosus var. comosus). A structural study comparing epidermal differences in pineapple cultivars resistant and susceptible to fusariosis was performed, relating properties of the epidermis to known susceptibility to the disease. The basal, non-chlorophylled, portions of mature leaves of pineapple plants were analyzed by light and electron microscopy. All cultivars showed common morpho-anatomic aspects characteristic of Bromeliaceae, such as scutiform scales and unstratified epidermis. However, cultivar Vitoria (resistant) had less scales than cultivars Smooth Cayenne (susceptible, intermediate severity) and Perola (susceptible, with extreme severity of fusariosis symptoms). Inoculation of conidia suspension (10⁵ conidia ml⁻¹) of the fungus F. guttiforme to leaves and harvesting 24 h later yielded numbers of viable colonies related to the density of leaf scales. This suggests that scales can act as havens for fungal conidia and favour the epiphytic stage of the fungus on pineapple plants, and are involved in the interaction of plant and pathogen. A reduction in scale numbers was related to lower infection levels and is relevant to the future breeding programme for development of new pineapple cultivars resistant to fusariosis and their involvement in integrated control strategies.     

Mycoparasitic Trichoderma viride as a biocontrol agent against Fusarium oxysporum f. sp. adzuki and Pythium arrhenomanes and as a growth promoter of soybean

Trichoderma viride was proved as an effective biocontrol agent against two fungal pathogens, Fusarium oxysporum f. sp. adzuki and Pythium arrhenomanes, infecting soybean. During an in vitro biocontrol test, Trichoderma showed mycoparasitism and destructive control against the tested fungal pathogens. Both the pathogens significantly influence the germination and P. arrhenomanes had a severe effect (only 5% germination). The root system of the soybean plant was poorly developed due to the infection and it exerted a negative influence on the nodulation and further growth phases of the plant. During pot assay along with biocontrol activity, Trichoderma showed growth promoting action on the soybean plant. Trichoderma enhanced growth of shoot and root systems and fruit yield after 12 weeks of growth. Pythium and Fusarium infected plants treated with Trichoderma had ∼194% and 141% more height than pathogens alone. The fruit yield treated with Trichoderma was ∼66 per plant whereas the yield was only 41 for a control plant. The plants infected with Pythium and Fusarium and treated with Trichoderma had fruit yields of 43 and 53 respectively and those were 5 and 1.6 times higher than plants infected with pathogens.     

Mature watermelon vine decline: Suppression with fumigants of a soil-borne problem and association with Rhizopycnis vagum

Mature watermelon vine decline (MWVD) is a late-season disease of unknown etiology, characterized by vine collapse and discolored, much reduced root systems. While several new disorders in watermelon have been reported recently, this problem appears specific to the Midwest. To test for a biological cause and methods to suppress this disorder, soil was collected from two southern Indiana fields with histories of MWVD for microplot and greenhouse experiments. Watermelons grew best in microplots treated with methyl bromide or methyl iodide. Roots of plants growing in the untreated MWVD soil were severely necrotic; those from the fumigation treatments appeared healthy. In heating experiments, watermelon seedlings were grown in autoclaved soil mixed with 10% MWVD soil that was either untreated or heated at 40, 50, 60, 70 or 80 °C for 30 min. Watermelon plants in the untreated controls and the 40 and 50 °C treatments had reduced top dry weights with decreased fibrous roots and associated discoloration in contrast to treatments of equal to and greater than 60 °C. Representative cultures from necrotic roots were identified as Rhizopycnis vagum by morphological analysis and sequencing the ITS region of the ribosomal DNA. PCR analysis with specific primers confirmed that R. vagum was present in roots from untreated MWVD soil but not in symptomless roots. This is the first report of R. vagum associated with plants suffering from MWVD in Indiana and indicates that this fungus occurs much farther north in the U.S. than known previously.     

Management of bacterial wilt in tomatoes with thymol and acibenzolar-S-methyl

The combination of thymol, a monoterpene phenol compound originating from thyme, and acibenzolar-S-methyl (ASM; Actigard 50 WG), a systemic acquired resistance (SAR) inducer, was applied to tomato plants in field conditions to evaluate the effectiveness of both chemicals to control bacterial wilt. Thymol was applied as a soil fumigant at 9.43 kg per ha 24 h after soil infestation and seven days before transplanting. ASM was applied as a foliar spray at 3.59-8.98 ml per ha, once in the greenhouse and five times in the field. The field was inoculated by applying 50 ml of pathogen suspension (10⁷ cfu/ml) into each transplanting hole eight days prior to transplanting. The experiment was performed in 2006 and repeated in 2008 at the North Florida Research and Education Center in Quincy, FL. In 2006, the combination of ASM and thymol significantly reduced disease in the bacterial wilt tolerant genotype 7514 compared to thymol alone. In 2008, the combination of ASM and thymol significantly reduced disease and increased yield compared to the control, whereas ASM or thymol alone did not significantly reduce disease or increase yield compared to the control. This is the first report of the use of both thymol and ASM to control bacterial wilt on moderately resistant tomato cultivars. Based on this study, control of the pathogen can be achieved by using both chemicals and moderately resistant cultivars.     

Effects of Fusarium culmorum and water stress on durum wheat in Tunisia

The effects of water stress on Fusarium foot and root rot in durum wheat were investigated in growth chamber, greenhouse and field tests in Tunisia. In the seedling stage, emergence of six durum wheat cultivars in the growth chamber was significantly reduced by inoculation with Fusarium culmorum and water stress (P<0.0001), with more disease under drier conditions. Additionally, the tiller number per mature plant, the 1000 grain weight and disease severity in mature stage were reduced by inoculation in greenhouse studies. In a field test, inoculation with F. culmorum significantly reduced the yield (P<0.001), by more than 17% for Om Rabiaa and 38% for Karim, the two cultivars tested. Yield was also significantly affected by precipitation and irrigation levels. The severity of the disease, estimated by the percentage of white heads, was separately affected by the cultivar (P<0.001) and inoculation (P = 0.0004). Percentage of white heads was 1.5 and 2 × higher in inoculated plants than non-inoculated for Om Rabiaa and Karim cultivars, respectively. Disease severity was highest in treatments with the greatest water stress. This is the first detailed study of water stress and F. culmorum on durum wheat in Tunisia, and indicates that cultivar resistance and irrigation management may be important in the management of Fusarium foot rot.     

Two-year investigations on the integrated control of weeds and root parasites in Virginia bright tobacco (Nicotiana tabacum L.) in central Italy

The current revision of pesticides in the EU, including those for soil disinfection, will necessitate the introduction of alternative integrated methods for the control of weeds and parasites in tobacco production in Italy. The present study compared the effect of some soil fumigants, biocontrol agents, cover crops and mulching for the control of tobacco weeds and root parasites. The results show that the different soil fumigants had an important role in increasing tobacco yield, due to their ability to control weeds and the nematodes Meloidogyne incognita and Meloidogyne javanica. In particular, a typical nematicide like 1,3-dichloropropene did not control only nematodes but also Portulaca oleracea, a common weed in Italian tobacco fields. Fenamiphos, although showed a certain efficacy in controlling root-knot nematodes, did not generally have a satisfactory activity at the dose of 40 g m⁻¹; cover crops like Trifolium squarrosum and Eruca sativa and a commercial formulation composed by the endomycorrhizal fungi Glomus spp., the antagonistic fungi Trichoderma spp. and bacteria including Pseudomonas, Bacillus and Streptomyces (Micosat F, CCS Aosta, Italy), were not able to control root tobacco diseases. The investigations confirmed that a prolonged monoculture causes a reduction of black root rot. Soil fumigation and the use of Good Agricultural Practices (GAP), influencing the inoculum density of Chalara populations, can contribute to the maintenance or to the establishment of particularly unfavourable conditions for the saprophytic growth of the pathogen, leading to a lower development of the disease.     

干旱胁迫对不同倍性小麦和八倍体小黑麦苗期光合能力与抗氧化系统的影响

为了解小麦进化过程中不同基因组及染色体倍数对小麦抗旱能力的影响,以二倍体、四倍体、六倍体小麦和八倍体小黑麦为材料,研究了聚乙二醇(PEG-6000)胁迫1d和3d后不同倍性小麦和小黑麦叶绿素荧光、气体交换参数、活性氧含量以及抗氧化酶活性的变化。结果表明,干旱胁迫3d后不同倍性小麦和八倍体小黑麦的相对水含量和叶绿素含量显著减少,气孔导度、蒸腾速率、光系统II最大光化学效率(Fv/Fm)以及光系统II实际量子产量(ΦPSII)降低,而非光化学淬灭(NPQ)、活性氧和丙二醛(MDA)含量显著上升,其中二倍体小麦变化最明显。干旱胁迫下,超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)活性呈现不同变化,SOD和POD活性先增后降,CAT活性降低,而APX活性增加,其中六倍体小麦抗氧化酶活性增加最显著。