Sensitivity to fluopicolide of wild type isolates and biological characteristics of fluopicolide-resistant mutants in Pseudoperonospora cubensis

Cucurbit downy mildew caused by the oomycete pathogen Pseudoperonospora cubensis is a devastating disease that is distributed worldwide and affects cucumber in open fields and greenhouses. Fluopicolide, which was a novel systemic fungicide and was released in 2008, it is very effective in controlling downy mildew on cucumber and grape, potato late blight and pepper Phythophthora blight and reduces the loss caused by the diseases, but so far the potential for P. cubensis to develop resistance to fluopicolide has not been investigated. Hence, a laboratory study was undertaken to assess the risk of P. cubensis developing resistance to fluopicolide. Baseline sensitivity to fluopicolide was determined by using 75 P. cubensis isolates collected from cucumber-growing greenhouses in Hebei province, where no fluopicolide had been used for control of cucumber downy mildew before. Values of effective concentrations for 50% inhibition (EC₅₀) of sporulation ranged from 0.02 to 0.40 μg ml⁻¹ and were distributed as a unimodal curve, indicating that all 75 isolates were sensitive to fluopicolide. Sporangia of nine sensitive isolates were ultraviolet (UV)-irradiated, and four fluopicolide-resistant mutants were acquired at a mutation frequency of 7.4 × 10⁻⁷. Seven mutants resistant to fluopicolide were obtained from seven isolates by sporangia adaptation on fluopicolide-treated leaves of cucumber. The EC₅₀ values for all eleven fluopicolide-resistant mutants ranged from 3.37 to 13.06 μg ml⁻¹ with mean resistance factors of 7.9–118.0. After 10 sporangia transfers on fungicide-free leaves of cucumber, all eleven resistant mutants remained resistant to fluopicolide with mean resistance factors of 8.2–81.3. Seven resistant mutants from the selection for resistance and one resistant mutant from UV mutagenesis exhibited stable resistance; however, the other three resistant mutants from UV irradiation became significantly less resistant. Compared to their respective sensitive parents, the eleven resistant mutants exhibited diversity in latent period, infection frequency, lesion extension and sporulation ability. Five out of the eleven resistant mutants exhibited prolonged latent period and three out of the eleven resistant mutants provided decreased infection frequency (IF) compared to their respective parents, indicating that in some cases, resistance mutation might affect the latent period and IF of P. cubensis. There were significant differences in pathogenicity and ability to produce sporangia, but this seemed not to be caused by resistance mutation. No cross-resistance was detected between fluopicolide and azoxystrobin, metalaxyl, dimethomorph, or cymoxanil. In all, there could be a moderate to high risk of field populations of P. cubensis developing resistance to fluopicolide, and populations of P. cubensis should be monitored regularly for their shift of sensitivity over years of application.     

Fungitoxicity and synergism of mixtures of fluopicolide and pyraclostrobin against Phytophthora infestans

Fluopicolide and pyraclostrobin were new systemic fungicides with highly inhibitory activity on a broad spectrum of oomycetes, but so far the fungitoxicity of their mixtures on the different developmental stages of Phytophthora infestans and whether synergism exists have not been investigated. The joint-toxicity of the mixtures of fluopicolide with pyraclostrobin was determined against the different developmental stages (mycelial growth, zoospore release, cystospore germination and sporangial germination) of P. infestans and late blight on the leaf discs and the potted plants of potato, and whether the synergistic interaction exists in the mixtures of the two fungicides were evaluated in vitro and in vivo based on the synergistic ratios calculated with the Wadley formulas. The protective activity and curative activity against P. infestans and the efficacy duration in controlling potato late blight of the synergistic mixtures of the two fungicides were examined in this study. The results showed that mixtures of fluopicolide (F) and pyraclostrobin (P) at the ratios of 10:1 and 1:4 (F:P) exhibited synergistic interactions and had excellent inhibitory activity against almost all developmental stages of P. infestans. Synergistic interactions of the mixtures at the ratios of 1:4 and 10:1 (F:P) against the mycelial growth of metalaxyl-resistant isolates were more obvious than against the mycelial growth of metalaxyl-sensitive isolates. Synergistic interactions of the mixtures at the ratio of 1:4 (F:P) against the mycelial growth of the most of the tested isolates were more obvious than those of the mixtures at the ratio of 10:1 (F:P). The highest activity of the mixtures was observed against zoospore release at the ratio of 1:4 (F:P) with EC₅₀ value of 0.0044 μg ml⁻¹. The strongest synergistic interaction of the mixtures was observed against zoospore release at the ratio of 10:1 (F:P) with the synergistic ratio of 5.27. The mixtures of fluopicolide and pyraclostrobin at the ratios of 1:4 and 10:1 (F:P) showed synergistic interactions against P. infestans on the leaf discs and intact plants of potato. The EC₅₀ values for protective activity and curative activity of the mixture at the ratio of 10:1 (F:P) were 0.63 μg ml⁻¹ and 0.87 μg ml⁻¹, and EC₅₀ values of protective activity and curative activity of the mixture at the ratio of 1:4 (F:P) were 0.27 μg ml⁻¹ and 0.44 μg ml⁻¹, respectively. At 14 days after spraying of fungicide solutions, the disease control efficacy of the mixtures at the ratios of 10:1 and 1:4 (F:P) was still over 80% at the dosages of 50 μg ml⁻¹ and 100 μg ml⁻¹, and the disease control efficacy of the two mixtures remained at about 97% at the dosages of 200 μg ml⁻¹, indicating long-lasting effective control efficacy of the two fungicides against potato late blight.     

Application of acibenzolar-S-methyl and standard fungicides for control of Phytophthora blight on squash

A plant systemic acquired resistance inducer, acibenzolar-S-methyl (ASM), was evaluated to determine the efficacy for suppression of Phytophthora blight of squash caused by Phytophthora capsici under field conditions. ASM was applied as foliar sprays before and after transplanting at rates of 17.5, 8.8, and 4.4 g a.i. ha⁻¹. Application of ASM did not significantly reduce final Phytophthora blight incidences in 2 out of 3 field experiments; however, area under the disease progress curve (AUDPC) values were reduced significantly by ASM in all experiments conducted. Disease suppression by the three application rates of ASM was not significantly different. To determine the effect of application of ASM in conjunction with standard chemical fungicides, ASM was applied with mefenoxam (Ridomil Gold), copper hydroxide, and mandipropamid (Revus). AUDPC values and final disease incidences were consistently lower in field plots treated by the combination of ASM and standard fungicides than applications of these chemicals alone. Application of ASM resulted in significantly higher squash yield than the non-treated control in 2 of 3 experiments and plots treated with the combined use of ASM and standard fungicides produced the highest yields. These results suggest that ASM may induce plant resistance under field conditions, providing suppression of Phytophthora blight of squash, and that there may be some benefit to the integration of ASM and standard chemical fungicides.     

Effects of oxathiapiprolin on Phytophthora nicotianae,the causal agent of black shank of tobacco

Oxathiapiprolin is a new fungicide active against oomycetes. In vitro assays and field studies were conducted to examine the effect of oxathiapiprolin on Phytophthora nicotianae (Pn), the causal agent of black shank. The efficacy of oxathiapiprolin on mycelial growth, sporangia production, zoospore motility, and zoospore germination was assessed with four Pn isolates. EC₅₀ values were low ranging from 0.0039 to 0.0049 μg a.i./mL for mycelial growth, 0.00052–0.00081 μg a.i./mL for sporangia production, 0.0035–0.0051 μg a.i./mL for encysted zoospore germination, and 0.0055–0.0166 μg a.i./mL for zoospore motility. Sixty six Pn isolates, 60 from tobacco and six from ornamental plants were examined for sensitivity to oxathiapiprolin at 1 μg a.i./mL. Mycelial growth at 1 μg a.i./mL was observed in only one isolate from tobacco whereas the six Pn isolates from ornamental plants five of which were resistant to mefenoxam at 100 μg a.i./mL, were found to be sensitive to oxathiapiprolin. The efficacy of oxathiapiprolin against black shank was assessed in three field studies in North Carolina. Treatments of oxathiapiprolin were equal or superior to mefenoxam against black shank in each field study. Our results suggest that oxathiapiprolin is a highly efficacious fungicide against P. nicotianae, and will be a useful tool in controlling black shank of tobacco.     

Actinomycetes mediated biochemical responses in tomato (Solanum lycopersicum) enhances bioprotection against Rhizoctonia solani

Six actinomycetes isolates, namely Streptomyces toxytricini vh6, Streptomyces flavotricini vh8, S. toxytricini vh22, Streptomyces avidinii vh32, Streptomyces tricolor vh85 and vh41, an isolate of an unknown species of Actinomycetales, were tested for their efficacy in protecting tomato (Solanum lycopersicum) against Rhizoctonia solani under green house conditions. Actinomycetes treated plants showed better growth in terms of high chlorophyll content, higher phenylalanine ammonia lyase (PAL) activity and high total phenolic content. Qualitative and quantitative estimation of phenolic compounds from tomato leaves showed significant accumulation of six phenolic acids, gallic (29.02 μg g⁻¹ fresh leaf wt), ferulic (11.44 μg g⁻¹ fresh wt), cinnamic (56.84 μg g⁻¹ fresh wt), gentisic (24.19 μg g⁻¹ fresh wt), chlorogenic acid (1.72 μg g⁻¹ fresh wt) and salicylic (0.39 μg g⁻¹ fresh wt) acid, in actinomycetes treated plants. Biochemical profiling, when correlated with plant mortality in actinomycetes treated and untreated plants, indicated that isolates vh6 and vh8 offered 44.55% and 40.14% disease reductions, respectively compared to the control. These results established that these organisms have the potential to act as biocontrol agents.     

Effect of boron on the development of brown rot (Monilinia laxa) on peaches

Requirements of consumers for products with low residues of pesticides have increased the need for alternative disease management practices. The concentration of boron in fruit affects its quality, shelf life and the development of physiological disorders. However, the effect of boron on the susceptibility of peach to fruit rots has not been reported. This study investigated the effect of boron (Power B and Borax) on the development of Monilinia laxa on peaches (cv Andross). Mycelial growth of M. laxa was inhibited on potato dextrose agar supplemented with 750 μg ml⁻¹ of Borax or 1000 μg ml⁻¹ of Power B. The EC 50 values were 107.9 and 522.4 for Borax and Power B respectively. Field investigations showed that the incidence of peach infections by M. laxa was negatively correlated with the content of Boron in the leaves. Post-harvest dipping of peaches in Power B or Borax solution, at concentrations recommended by manufacturer (2 μg ml⁻¹ for Power B and 1 mg ml⁻¹ for Borax), significantly reduced the development of M. laxa. Power B, at rates of 6 μg ml⁻¹, and Borax at rates of 3 mg ml⁻¹ were the most effective in reducing infections by M. laxa. Finally, post-harvest dipping of fruit in Power B or Borax reduced losses of fruit weight and improved fruit firmness one month after storage, showing that boron increased the maintainability of peaches in cold storage. Peaches treated with 6 μg ml⁻¹ Power B or 3 mg ml⁻¹ Borax had the highest flesh firmness and the lowest water losses, while untreated control peaches were the least firm. Generally, Borax was significantly less effective than Power B, but better than the control treatment.     

Baseline and differential sensitivity to mandipropamid among isolates of Peronophythora litchii, the causal agent of downy blight on litchi

Litchi downy blight caused by Peronophythora litchii is a devastating disease of litchi plants in China. Control of litchi downy blight requires numerous fungicide applications. A new carboxylic acid amide (CAA) fungicide, mandipropamid, was examined for its in vitro effects on multiple asexual stages of four single-sporangium P. litchii isolates and protective activity against downy blight in detached fruit assays. Though mandipropamid did not affect discharge of zoospores from sporangia, it strongly inhibited mycelial growth (mean EC₅₀ = 0.0048 μg ml⁻¹), sporangia production (mean EC₅₀ = 0.0032 μg ml⁻¹), germination of encysted zoospores (mean EC₅₀ = 0.0023 μg ml⁻¹), and germination of sporangia (mean EC₅₀ = 0.0061 μg ml⁻¹). On detached fruit, 0.39, 1.56 and 6.25 μg ml⁻¹ of mandipropamid were superior in reducing downy blight compared to metalaxyl and flumorph, however, the 25 μg ml⁻¹ application rate was necessary for all three CAA fungicides to completely inhibit the disease. In 2007, 100 isolates from Fujian, Guangdong, and Guangxi Provinces of China were characterized for the baseline sensitivity to mandipropamid. The isolates obtained from different provinces showed similar baseline sensitivities to mandipropamid. Baseline sensitivities formed a unimodal curve with mean EC₅₀ values of 0.0055 ± 0.0012 μg ml⁻¹ for inhibition of mycelial growth. The described baseline sensitivities of P. litchii populations will be useful for monitoring possible shifts in sensitivity to mandipropamid.     

Inheritance of mefenoxam resistance in selfed populations of the homothallic oomycetePhytophthora erythroseptica (Pethybr.), cause of pink rot of potato

The inheritance of mefenoxam resistance in the oomycetePhytophthora erythroseptica, causal organism of pink rot of potato, was investigated in two successive selfed generations of single oospore isolates. Fourteen parental isolates from three mefenoxam-sensitivity phenotypes (sensitive, intermediately resistant, and resistant) were used to produce S1 and S2 progeny isolates by selfing each isolate and germinating single oospore cultures from each isolate. The two generations of isolates were tested for mefenoxam sensitivity using the radial growth inhibition assay and calculating EC₅₀ values. Twenty-four-hundred isolates from S1 and S2 generations were tested for mefenoxam sensitivity. Results demonstrated the lack of segregation for mefenoxam sensitivity among S1 and S2 progeny isolates from the resistant and sensitive parents. The majority of the S1 progeny isolates from the parents with intermediate resistance also possessed intermediate resistance, but demonstrated substantial quantitative shifts in response to mefenoxam more often toward increased insensitivity. A few isolates from the S1 progeny were sensitive to mefenoxam, and one isolate was mefenoxam-resistant. Similarly, the majority of the S2 progeny isolates from intermediately resistant parents also possessed intermediate resistance with some quantitative shifts in sensitivity to mefenoxam similar to those observed in S1 progeny, as well as a few isolates that were sensitive to mefenoxam. These results do not support the hypothesis that resistance to mefenoxam inP. erythroseptica is controlled by a single gene exhibiting incomplete dominance. Alternative hypotheses are proposed such as the genetics of mefenoxam resistance inP. erythroseptica is probably under the control of more than one major gene and perhaps some minor genes of additive effect.     

Efficacy and effects on yield of different fungicides for control of wet bubble disease of mushroom caused by the mycoparasite Mycogone perniciosa

Carbendazim, iprodione, prochloraz-Mn, thiabendazole and thiophanate-methyl were tested in vitro and in vivo for their effect on Mycogone perniciosa, the mycoparasite that causes wet bubble disease of white button mushroom. In vitro experiments showed that prochloraz-Mn (ED₅₀ = 0.006–0.064 μg ml⁻¹) and carbendazim (ED₅₀ = 0.031–0.097 μg ml⁻¹) were the most effective fungicides for inhibiting the mycelial growth of M. perniciosa, while iprodione (ED₅₀ = 1.90–3.80 μg ml⁻¹) was the least effective. The resistance factors calculated for the five fungicides were between 1.4 and 2. The results obtained suggest that there is very little risk that M. perniciosa will develop resistance to the fungicides assayed. The in vivo efficacy of fungicides for control of wet bubble was studied in two mushroom cropping experiments, which were artificially infected with two doses of M. perniciosa, 10⁶ and 10⁷ spores m⁻², respectively. There was, in the low dose inoculum experiment, a very high degree of effectiveness (96.5–100.0%) with all the fungicides assayed. However, iprodione performed poorly (20.5–24.4%) compared with the other fungicides (88.7–100.0%) in the high concentration inoculum experiment. The most effective treatments for controlling wet bubble did not improve the biological efficiency of Agaricus bisporus.     

Sensitivity of Phytophthora parasitica to mandipropamid: In vitro determination of baseline sensitivity and in vivo fungitoxicity

Tobacco black shank caused by Phytophthora parasitica is a devastating soil-borne disease of tobacco in China. Control of tobacco black shank relies on numerous fungicide applications. A new carboxylic acid amide (CAA) fungicide, mandipropamid, was examined for its effects on various asexual developmental stages of P. parasitica in vitro and in tobacco seedlings. Although mandipropamid did not affect discharge of zoospores from sporangia, it strongly inhibited mycelial growth (mean EC₅₀ value of 0.0112 μg ml⁻¹), sporangia production (mean EC₅₀ value of 0.009 μg ml⁻¹), germination of encysted zoospores (mean EC₅₀ value of 0.014 μg ml⁻¹), and germination of sporangia (mean EC₅₀ value of 0.017 μg ml⁻¹). For protective activity in tobacco seedlings, various applications of mandipropamid were superior in reducing black shank compared to that of metalaxyl and of azoxystrobin; while for curative activity assay, 100 μg ml⁻¹ of mandipropamid exhibited the same efficacy as that of metalaxyl, and presented superior activity than that of azoxystrobin. In 2010 and 2011, 119 isolates of P. parasitica from Guizhou Province of China were characterized for the baseline sensitivity to mandipropamid by measuring mycelial growth. Values of effective concentrations for 50% mycelia growth inhibition varied from 0.0068 to 0.0285 μg ml⁻¹ and averaged 0.013 (±0.0045) μg ml⁻¹, with a unimodal distribution. This information will serve as a baseline for tracking future changes in sensitivities of P. parasitica populations to mandipropamid in China.     

Potential of extracts of the tropical plant Balanites aegyptiaca (L) Del. (Balanitaceae) to control the mealy bug, Maconellicoccus hirsutus (Homoptera: Pseudococcidae)

The effects of extracts of different parts of the perennial tropical plant Balanites aegyptiaca (L) Del., including various solvent extracts of roots, methanol extracts from leaves, fruits, flowers and roots, partially purified saponins obtained from its roots and a standard saponin were studied on the life cycle (adult longevity, number of eggs, crawlers, adults, weight of adults and % wax content) of a laboratory-reared parthenogenic line of the mealy bug, Maconellicoccus hirsutus (Homoptera: Pseudococcidae). Extracts derived from various parts of B. aegyptiaca (leaves, fruits, flowers, and roots in methanol) affected the life cycle of M. hirsutus with a methanol root extract being the most effective at a concentration of 500 μg ml⁻¹. Partially purified saponin of B. aegyptiaca and the commercial bark saponin extract (Sigma) from Quillaja saponaria at a concentration of 500 μg ml⁻¹ were effective in reducing the longevity of M. hirsutus. Significant reductions in oviposition by M. hirsutus were found for all the extracts at a concentration of 500 μg ml⁻¹. Extracts also affected the number of emerging crawlers, number of adults as well as the weight and wax content of emerging adults. These studies suggest that B. aegyptiaca plant extracts and saponins can be useful botanical insecticides for the protection of crops from mealy bugs.     

Activities of essential oils from Asarum heterotropoides var. mandshuricum against five phytopathogens

Some secondary metabolites of plants function as antimicrobial products against phytopathogens and constitute an increasingly important class of pesticides. In the present study, the essential oil of Asarum heterotropoides var. mandshuricum was analyzed by GC/MS and its antimicrobial activity was evaluated against five phytopathogenic fungi. Major components of the oil were methyleugenol (59.42%), eucarvone (24.10%), 5-allyl-1,2,3-trimethoxybenzene (5.72%), and 3,7,7-trimethylbicyclo(4.1.0)hept-3-ene (4.93%). The essential oil and the most abundant component, methyleugenol, were separately assayed for inhibition of 5 pathogens: Alternaria humicola, Colletotrichum gloeosporioides, Rhizoctonia solani, Phytophthora cactorum and Fusarium solani. Both the oil and methyleugenol strongly inhibited the growth of the test pathogens (IC₅₀ values <0.42 μg ml⁻¹) except F. solani, with the best activity against P. cactorum (IC₅₀ values = 0.073 and 0.052 μg ml⁻¹, respectively). It is concluded that the essential oil of A. heterotropoides var. mandshuricum has a broad antiphytopathogenic spectrum, and that methyleugenol is largely responsible for the bioactivity of the oil. The mode of action of methyleugenol against P. cactorum is discussed based on changes in the mycelial ultrastructure.     

Occurrence and characterization of fungi and oomycetes transmitted via potting mixtures and organic manures

A study was conducted to investigate the most common fungal and oomycete pathogens introduced into farms in Oman via potting mixtures and organic manures. A total of 37 commercial types of potting mixtures (2 local and 35 imported from overseas), 4 commercial types of organic manures and 11 non-commercial types of organic manures were included in the study. Identification of the isolated species was based on morphological characteristics, except for the most common species which were further identified using sequences of the internal transcribed spacer region of the ribosomal DNA (ITS rDNA). Fusarium spp. (14%), Pythium aphanidermatum (3%), Alternaria spp. (5%), Helminthosporium spp. (5%) and Cladosporium spp. (3%) were recovered at different frequencies from samples of potting mixtures. Fusarium solani (40%) and Fusarium equiseti (47%) were recovered at high frequencies from samples of organic manures. Isolations from organic manures also yielded Pythium periplocum (7%), Rhizoctonia solani (7%), Fusarium lichenicola (7%), Helminthosporium spp. (27%) and Alternaria spp. (27%). Trichoderma spp., Penicillium spp., Aspergillus spp. and Rhizopus spp. were found to be common in samples of potting mixtures and organic manures. Investigating sensitivity to hymexazol among 9 isolates of F. equiseti and 13 isolates of F. solani revealed variations among different isolates. The EC₅₀ values ranged from 1 to over 1200 (avg. 192 μg ml⁻¹) for F. equiseti isolates and from 135 to 789 (avg. 324 μg ml⁻¹) for F. solani isolates, indicating presence of resistance to this important fungicide among some Fusarium isolates. This appears to be the first report of contamination with R. solani, P. periplocum, F. solani, F. equiseti and F. lichenicola of organic manures. This study appears to report for the first time F. lichenicola in Oman and appears to be the first report of occurrence of resistance to hymexazol among F. equiseti and F. solani isolates.     

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.     

Race distribution and distribution of sensitivities to mefenoxam among isolates of Phytophthora parasitica var. nicotianae in Guizhou province of China

Black shank, caused by the hemibiotrophic oomycete Phytophthora parasitica var. nicotianae, is a major disease of tobacco (Nicotiana tabacum) in southwest China. Mefenoxam is one of the most commonly used fungicides for its management. A survey was conducted to determine the level of mefenoxam sensitivity in the pathogen population in Guizhou province and to determine the race distribution of selected isolates. In 2012, 179 isolates of P. parasitica were screened for sensitivity to mefenoxam on lima bean agar. Zero percent of the isolates was classified as resistant, 41.9% as intermediately resistant, and 58.1% as sensitive. Race was determined for 32 isolates from 12 tobacco districts using five discriminative cultivars: NC-1071, Fla 301, L8, Xiaohuangjing 1025 and K-326. Twenty seven isolates were race 1 and five were race 0. Race 1 was present in all regions sampled and presents a major concern for the use of tobacco cultivars in Guizhou province in the future. Based on the results of our survey, we conclude that a combination of practices that includes partial resistance, cultural controls, and fungicides will be needed for long term management of tobacco black shank in Guizhou province of China.     

Wheat grain tissue proportions in milling fractions using biochemical marker measurements: Application to different wheat cultivars

Measurement of biochemical markers allows the quantification of wheat (Triticum spp.) grain tissue proportions in milling fractions. In order to evaluate the ability of extending this methodology to an unknown wheat grain batch, the variability of the markers in the different tissues was assessed on various wheat cultivars. Ferulic acid trimer amounts in the outer pericarp ranged from 0.97 to 1.67 μg mg⁻¹ (dm) with an average value equal to 1.31 μg mg⁻¹ (dm). Alkylresorcinols amounts in a composite layer, including the testa, the inner pericarp and the nucellar epidermis, ranged from 10.5 to 16.7 mg g⁻¹ (dm), with an average value equal to 14.0 mg g⁻¹ (dm). In the aleurone layer, phytic acid amounts ranged from 94.9 to 187.2 mg g⁻¹ (dm) with an average value equal to 152 mg g⁻¹ (dm) whereas, para-coumaric acid ranged from 0.08 to 0.29 μg mg⁻¹ with an average level of 0.18 μg mg⁻¹. In the embryonic axis, wheat germ agglutinin ranged from 879 μg g⁻¹ to 2086 μg g⁻¹ with an average value of 1487 μg g⁻¹. The impact of this variability on tissue proportion determination was evaluated and a strategy to decrease the prediction error was suggested. Percentages of the outer pericarp, intermediate layer (including the testa), aleurone layer and embryonic axis within grains were calculated and their variability discussed.     

Nematicidal efficacy of isothiocyanates against root-knot nematode Meloidogyne javanica in cucumber

Isothiocyanates (ITCs), a series of new nematicides of the -NCS group, were evaluated for their efficacy against root-knot nematode Meloidogyne javanica. Of the compounds tested, AllylITC, AcITC, EtITC, BzTC, BzITC, 1-PEITC and 2-PEITC showed in vitro irreversible nematicidal activity against second-stage juveniles of M. javanica, following exposure for 72 h at concentrations as low as 5 μg mL⁻¹. When exposed to AllylITC, AcITC and EtITC at lower concentrations, motile juveniles also became irreversibly immobile in 3 days, with a LC₅₀ value at 2.76, 2.53 and 3.05 μg mL⁻¹, respectively. In the pot experiments, 1.0 ml AllylITC and 1.1 ml AcITC per kg of soil controlled M. javanica, similarly to or better than metam sodium at its recommended dose. Similar results were obtained in the field experiments using 1.0 kg AllylITC or 1.0 kg AcITC ha⁻¹. Based on the results of this study, AllylITC and AcITC have potential to be used as new bio-fumigant nematicides.     

Resistance in watermelon rootstocks to crown rot caused by Phytophthora capsici

Crown rot caused by Phytophthora capsici is becoming an increasingly important disease of vegetable crops in southeastern U.S. In recent years, the practice of grafting watermelon onto rootstocks belonging to other Cucurbitaceae genera has also been slowly gaining adoption in the U.S. However, it is not known how these rootstocks, developed mainly in Asia, will respond to diseases prevalent in local production areas. We evaluated the available commercial watermelon rootstocks for resistance to Phytophthora crown rot by inoculating them with a zoospore suspension of P. capsici in four different trials. Disease development on rootstocks was rated on a 1–9 scale (1 = no symptoms, 9 = plant dead). Based on all the four trials, the commercial Lagenaria siceraria (bottle gourd) rootstocks, FR-Strong, Emphasis, Macis and WMXP-3938 were resistant (Mean rating ≤3) to crown rot when compared to susceptible watermelon checks (mean rating >8). All Cucurbita inter-specific hybrid rootstocks and a watermelon rootstock Ojakkyo, were highly susceptible to crown rot (mean rating >8). Real-time quantitative polymerase chain reaction (qPCR) using two different P. capsici specific primers (ITS and β-tubulin) indicated the presence of significantly (P < 0.0001) greater amounts of P. capsici DNA g⁻¹ plant tissue in susceptible Cucurbita inter-specific hybrid rootstocks (β-tubulin, mean = 2895 ng) and watermelon (2665 ng) compared to the L. siceraria rootstocks (357 ng). Crown rot resistant bottle gourd rootstocks may be useful in areas where P. capsici is a recurring problem. The present study identified several commercial bottle gourd rootstocks with resistance to Phytophthora crown rot, and confirmed their levels of resistance using qPCR.     

Characterization and Distribution of Three New Clonal Lineages of Phytophthora infestans Causing Late Blight in Wisconsin from 2009 to 2012

Phytophthora infestans causes late blight of potato and tomato, a disease that has been estimated to cost U.S. potato growers $287.8 million annually. We collected isolates of P. infestans from Wisconsin from 2009 to 2012 and determined distribution of clonal lineages and mating types and sensitivity to the systemic fungicide mefenoxam. We also sought to evaluate the current utility of an analysis of the Glucose-6-phosphate isomerase (Gpi) allozyme locus for predicting mefenoxam sensitivity with the aim of delivering timely information to growers. Overall, 143 isolates were collected from 52 locations in 20 Wisconsin counties from 2009 to 2012. Three clonal lineages, US-22, US-23, and US-24, were identified and were novel to Wisconsin and the U.S. US-22 is of the A2 mating type and sensitive to mefenoxam, with Gpi 100/122. US-23 and US-24 are of the A1 mating type and primarily intermediately sensitive to mefenoxam, with Gpi 100/100 and 100/100/111, respectively. Because of this close correlation and the unique Gpi patterns for each lineage present, we were able to predict mefenoxam sensitivity directly from samples using the allozyme assay and quickly deliver management information to growers. Both mating types were present in Wisconsin in 2009 and 2010 but were spatially separated and no evidence of sexual recombination or soil persistence was detected. The presence of new clonal lineages of P. infestans in Wisconsin indicates a need for continued close monitoring of late blight to facilitate generation of timely information for enhanced short-term and long-term late blight management.     

Insecticidal activities of crude extracts and phospholipids from Chenopodium ficifolium against melon and cotton aphid, Aphis gossypii

Several organic solvent extracts of Chenopodium ficifolium were tested for their insecticidal activity against melon and cotton aphid, Aphis gossypii, on cucumber plants. Both methanol and ethanol extracts, at 5000 μg ml⁻¹, were highly active giving over 80% control. The other crude extracts displayed moderate or weak insecticidal activity giving control in the range of 16–69%. Two phospholipids were isolated as insecticidal active substances from C. ficifolium. Their chemical structures were identified as 1-palmitoyl-2-(3-trans)-hexadecenoyl-sn-glycero-3-phosphoglycerol and 1-palmitoyl-2-linoleoyl-3-glycerophosphocholine by GC–MS, EDS, mass and NMR spectral analyses. Both compounds displayed a dose-dependent mortality of A. gossypii. Furthermore, the liquid formulation that was obtained by partitioning with n-hexane from the methanol extract of C. ficifolium controlled melon and cotton aphid on cucumber plants effectively. These results indicate that extracts of C. ficifolium have potential for development as botanical insecticides for controlling A. gossypii infesting cucumber plants.