Development of black dot disease (Colletotrichum coccodes (Wallr.) Hughes) and its effects on the growth and yield of potato plants

Seed tubers of cvs Désirée and Pentland Crown with different severities of black dot were planted in 1988 and 1989 at Rothamsted in fields in 4– or 7-course rotations, respectively. Tubers treated with prochloraz (1988) or imazalil (1989) were planted in some plots, and in others Colletotrichum coccodes inoculum was added to the soil at planting. In further experiments at Mepal, Cambridgeshire in 1989 and 1990 and at Rothamsted in 1990 on sites where potatoes had not been grown for more than 15 years, large amounts of inoculum were added to the soil around disease-free seed tubers of two (1989) or three (1990) cultivars at planting. In all experiments plants were sampled during the season and the effects of treatments on disease development, growth and yield were recorded. Disease on roots, stem bases and tubers was found early in the season and was more severe on Désirée than on Pentland Crown plants from fields in 4– or 7-course rotations. Severity increased throughout the season and with increasing amounts of disease on the seed tubers, especially with Desiree. Disease was also found on plants from disease-free tubers and was more severe in 1988 than 1989. At harvest, black dot on tubers was significantly more severe from severely affected than from disease-free seed, and was most severe where inoculum, especially large amounts, had been added at planting. Fungicide treatment decreased disease early in the season but had no effect on tuber infection at harvest. In 1989 the weight loss of seed tubers during sprouting increased with increasing amounts of black dot, but the disease had little effect on plant size through the season. At harvest the yield of ware tubers (>50 mm) decreased with severe disease but total tuber yields were not significantly affected. However, at harvest in 1988 severely affected seed yielded significantly less than healthy seed. Plants grown from mini-tubers were free from disease on sites where potatoes had not been grown for at least 15 years. Inoculum applied at planting caused severe disease on all cultivars in both years, whereas disease was slight on uninoculated plants. Inoculated plants senesced early at Mepal in 1990, but there were no significant differences in total tuber yield in any experiment. However, yields of ware tubers (>50 mm) were sometimes decreased and the total tuber number per plant increased.     

The effect of treating seed potato tubers with benzimidazole, imidazole and phenylpyrrole fungicides on the control of rot and skin blemish diseases

Over 6 yr the effectiveness of imazalil, prochloraz and fenpiclonil, applied either alone or in a mixture, in controlling gangrene, dry rot, skin spot and silver scurf on potato tubers in store was compared with that of 2-aminobutane and thiabendazole. An assessment was also made of their efficiency in controlling the development of these diseases on the daughter tubers of seed tubers treated at harvest or before planting. Overall, 2-aminobutane was more effective in controlling gangrene (Phoma foveata) in store than the spray-applied fungicides. Deposits of imazalil, thiabendazole and fenpiclonil were greater when sprays were applied with an electrostatic sprayer than with a hydraulic sprayer. The opposite was found with the mixture of prochloraz Mn and tolclofos-methyl. More effective gangrene control was associated with the highest deposits. Fenpiclonil and the mixture of thiabendazole and imazalil were more effective in controlling dry rot (Fusarium solani var. coeruleum) than imazalil alone. The development of dry rot was, however, increased by 2-aminobutane treatment on eight out of 14 stocks. 2-aminobutane gave the greatest reduction (83%) in the severity of skin spot during storage whereas thiabendazole alone, and the mixture of thiabendazole and imazalil, gave mean reductions of 70% and 65% respectively. This mixture and fenpiclonil gave the greatest reduction in the severity of silver scurf although, in general, reductions in silver scurf with fungicide treatment were less than with skin spot. The type of sprayer used to apply a fungicide did not affect the effectiveness of the fungicides in controlling either skin spot or silver scurf on tubers in store, or on the daughter tubers. The incidence of gangrene and dry rot on daughter tubers was not reduced consistently by fungicide treatment of seed tubers of the six stocks tested. However, the severity of skin spot and silver scurf was reduced by fungicide treatments of all eight stocks but the reduction in disease was greater for skin spot than for silver scurf. All fungicides gave reductions in the severity of skin spot, and fenpiclonil and the mixture of thiabendazole and imazalil were the most effective for silver scurf. The effectiveness of the fungicides in controlling these diseases was similar for seed treated at harvest and that treated before planting.     

不同粒度羧甲基壳聚糖基复合抗菌剂抑菌性能的研究

为增加固体制剂的水溶性以及考查研磨后其抗菌性能的变化,制备了低银含量和低噻苯咪唑含量的羧甲基壳聚糖银噻苯咪唑（Ag—CMCTS-TBZ）复合抗菌剂,通过研磨和粒度分级将其分成C1（150—74μm）、C2（74—45m）和C3（-45μm）三种制剂,采用粒度分析、紫外、红外光谱及最小抑菌浓度（MIC）对其进行分析。研究表明,低含量银、噻苯咪唑的Ag—C／VICIS—TB均具有良好的水溶性,其溶解度都大于0．4％,其0．2％（w／v）的抗菌水溶液中的表观粒度在13—250nm之间;但在研磨分级之后,三种制剂中分子间的络合或者氢键键合状况发生了变化,而且导致其抗菌性能发生改变;其中C1对E．coli和S．aureus有较强的抑制,而其抑制A．niger的能力较弱;C3抗菌活性最低,对E．coli,S．aureus,C．albicans和A．niger的MIC值皆〉1000mg／L;Q的抗菌效果则介于其间。     

Biological Control of Postharvest Diseases of Apple and Pear under Semi-commercial and Commercial Conditions Using Three Saprophytic Yeasts

The yeastsCryptococcus laurentii(strain HRA5),Cryptococcus infirmominiatus(strain YY6), andRhodotorula glutinis(strain HRB6) were tested as biocontrol agents of postharvest diseases of apple and pear in semi-commercial and commercial trials. The yeasts effectively controlled decay when applied in a drench or line spray. The yeasts were not adversely affected when treated fruits were stored in a controlled atmosphere consisting of 1% oxygen and 99% nitrogen. In a commercial trial, the most effective treatments for control of blue mold of pear were a combination ofC. laurentiiandC. infirmo-miniatus(91% control) and the commercially recommended high rate (528 μg/ml) of thiabendazole (88% control). In the commercial apple trial, the most effective treatments for blue mold wereC. infirmo-miniatuscombined with 264 μg/ml thiabendazole (91% control),C. infirmo-miniatuscombined withC. laurentii(84% control), and thiabendazole alone at 528 μg/ml (79% control). The combination ofC. laurentiiwith 264 μg/ml of thiabendazole was significantly more effective for control of blue mold on pear than thiabendazole at 528 μg/ml whenever any thiabendazole-resistant spores were present in the inoculum.     

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.     

The effect of selection with levamisole on benzimidazole resistance in Ostertagia spp. of sheep

A field population of Ostertagia spp. (predominantly O. circumcincta) in sheep, found to be resistant to oxfendazole, was exposed to selection with1 levamisole in the laboratory and the field. Progeny of the survivors of a single dose of levamisole in penned sheep showed a significantly lower level of resistance to oxfendazole in an anthelmintic assay, and a similarly lower level of resistance to the ovicidal activity of thiabendazole in vitro compared with the progeny of the survivors of a single dose of oxfendazole, although they remained more resistant than a known susceptible strain of 0. circumcincta. The progeny of worms present in grazing sheep after three doses of levamisole at 4-weekly intervals, and subjected to the same tests, behaved in a similar fashion. They also showed a substantial fall in benzimidazole resistance compared with the progeny of worms not exposed to any anthelmintic for 6 months. The results suggested that levamisole selected positively against benzimidazole resistance. In these circumstances some form of alternation in the use of different anthelmintics could delay the development of a high level of resistance and maintain the practical usefulness of existing anthelmintics.     

Succinate dehydrogenase and fumarate reductase activity in Aspiculuris tetraptera and Ascaris suum and the effect of the anthelmintics cambendazole,thiabendazole, and levamisole

Comley John C. W. and Wright Spdenis J. 1981. Succinate dehydrogenase and fumarate reductase activity in Aspiculuris tetraptera and Ascaris suum and the effect of the anthelmintics cambendazole, thiabendazole, and levamisole. International Journal for Parasitology11: 79–84. Succinate dehydrogenase and fumarate reductase activities from a particulate fraction of A. tetraptera and a soluble extract of A. suum have been determined using spectrophotometric methods. Fumarate reductase activity in A. suum could only be detected anaerobically. Succinate dehydrogenase activity from A. suum was partially characterized and shown to exist in several multimolecular forms (isoenzymes). The in vitro effect of the anthelmintics cambendazole, thiabendazole and levamisole on succinate dehydrogenase and fumarate reductase activity from the above nematodes are described. Significant inhibition of fumarate reductase activity of both nematodes was only achieved using 5 mM levamisole and 1 mM thiabendazole. After in vivo anthelmintic treatment of A. tetraptera only thiabendazole significantly inhibited fumarate reductase. It is suggested that the succinate dehydro-ogenase-fumarate reductase complex in these nematodes is unlikely to be the primary site chemotherapeutic attack for any of the anthelmintics tested.     

Resistance of selected lines of Ostertagia circumcincta to thiabendazole, morantel tartrate and levamisole

Le Jambre I. F., Southcott W. H. and Dash K. M. 1977. Resistance of selected lines of Ostertagia circumcincta to thiabendazole, morantel tartrate and levamisole. International Journal for Parasitology7: 473–479. A strain of Ostertagia circumcincta was isolated from a field in which all sheep had been treated in sequence every 7–10 days from September 1970 to January 1974 with either thiabendazole, morantel tartrate or levamisole. Thiabendazole had not been used after the first 15 months. The LD₉₅ for this strain was 88 mg/kg thiabendazole, 6.9 mg/kg morantel tartrate and 5-4 mg/kg levamisole.Another strain of O. circumcincta isolated from an area where anthelmintics had been used much less frequently was divided into four lines for exposure to selection in the laboratory. The first line was selected with 50 mg/kg thiabendazole, the second with 5 mg/kg morantel tartrate, and the third with 3.2 mg/kg levamisole; the fourth line was not selected for drug resistance. After eight generations the three lines selected with thiabendazole, morantel tartrate and levamisole had (Spld)(in95) of > 200, 5.7 and 6.2 mg/kg for the selecting drugs respectively, compared with corresponding values of 20, 2.9, and 1.8 in the unselected line. That is, the field strain had about the same levels of resistance to morantel tartrate and levamisole as the respective laboratory strains selected with these individual drugs. However, the field strain, which had been exposed to thiabendazole for only 15 months, was less resistant to thiabendazole than the laboratory strain selected with this drug. These results show that giving of several drugs in sequence cannot be relied upon to prevent the development of resistance to the individual drugs.The dose responses of adult worms showed low, but significant resistances to morantel tartrate and levamisole and a relatively high resistance to thiabendazole. Levamisole was found to select for inhibition of development with approx. 8.0% of the inhibited larvae showing no dose response above 1.6 mg/kg. Levamisole was also associated with an increase from 0.1 % to 9.0% in the O. trifurcata component of an Ostertagia population.     

Development of simultaneous resistance in Ostertagia circumcincta to thiabendazole, morantel tartrate and levamisole

Le Jambre L.F., Southcott W.H. and Dash K.M. 1978. Development of simultaneous resistance in Ostertagia circumcincta to thíabendazole, morentel tartrate and levamisole. International Journal for Parasitology8: 443–447. A field strain of Ostertagia circumcincta was divided into five strains based on anthelmintic selection in the laboratory. The first strain was selected with 50 mg/kg thiabendazole, the second with 4 mg/kg morantel tartrate, the third with 3.2 mg/kg levamisole, the fourth was not selected and the fifth strain was selected with all three anthelmintics in each generation. The present paper reports the dose response of the eighth generation of the multi-selected strain to thiabendazole, morantel tartrate and levamisole and compares these results with those from the eighth generation of the single selected and unselected strains.In adult O. circumcincta the LD₉₅ for thiabendazole, morantel tartrate and levamisole was 172.0, 9.2 and 8.4 mg/kg respectively in the multiselected strain, compared with corresponding values of > 200, 6.1 and 6.9 for the single selected strains and 14.5, 2.8 and < 1.6 in the unselected parent strain.Multiple selection with three anthelmintics was associated with an increase in O. trifurcata from less than 0.1 % in the unselected strain to 16% in the multi-selected strain.An increase in inhibition was a feature of both multiple selection and selection by levamisole alone. The parent strain had less than 0.1 % inhibition but the incidence increased to 16% in the levamisole selected strain and to 2% in the multi-selected strain. Approximately 8% of the inhibited larvae in the levamisole selected strain were resistant to dose levels of levamisole from 1.6 to 8.0 mg/kg. Resistance in inhibited larvae was further enhanced in the multi-selected strain and after eight generations 100% of larvae in this strain were resistant to all dose levels up to 100 mg/kg thia-bendazole, 20 mg/kg morantel tartrate and 8 mg/kg levamisole. Apparently when selected with anthelmintics that are less effective against larvae than adults, O. circumcincta responds by increasing the percentage and resistance of inhibited larvae.