Anti-sporulant activity was high with both strobilurin fungicides applied at concentrations of 10 or 20 μg ml-1 when applied after the appearance of the symptoms. The anti-sporulant activity of difenoconazole was similar to that of pyraclostrobin and trifloxystrobin applied at 5 μg ml-1, while chlorothalonil did not provide significant antisporulant activity.
Induced resistance to Leptosphaeria maculans (phoma stem canker) in Brassica napus by L. biglobosa and chemical defence activators in field and controlled environments
S. Y. Liuab, B. D. L. Fitta*†, N. Evansa, S. J. Fostera‡, Y. J. Huanga, Z. Liuac and J. A. Lucasa
a Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK; b Key Lab of Ministry of Agriculture for Genetic Improvement of Oil Crops, Oil Crops Research Institute, CAAS, Wuhan 430062, P.R. China; and c Crop Research Institute, Anhui Academy of Agricultural Sciences, Hefei 230031, P.R. China
Local and systemic resistance induced by weakly virulent European Leptosphaeria biglobosa and the chemical defence activators, acibenzolar-S-methyl (ASM) and menadione sodium bisulphate (MSB), against subsequent infection by L. maculans were studied under controlled environment and field conditions. Ascospore suspensions of both pathogens were used as inoculum. In controlled environment experiments, pre-treatments with L. boglobosa, ASM or MSB delayed infection by L. maculans. The treatments reduced the lesion size caused by L. maculans in both induced leaves (local resistance) and non-induced leaves (systemic resistance). These results were validated in field experiments for two seasons, 2002/2003 and 2003/2004. Pre-inoculation with L. biglobosa or spraying with ASM significantly reduced not only % natural infection and number of lesions per leaf caused by L. maculans early in the season, but also reduced severity of stem canker caused by L. maculans later in the season. ASM was more potent than L. biglobosa in inducing resistance.
Sensitivity of single spore isolates of Trichoderma harzianum and Cladobotryum dendroides to benzimidazole fungicides
Salem O. Abosriwil and Kevin J. Clancy
Dept. Environmental Resource Management, University College Dublin, Ireland
Effects of benomyl, carbendazim and thiabendazole on single spore isolates of Trichoderma harzianum and Cladobotryum dendroides, isolated from disease situations in commercial mushroom cultivation systems were evaluated in vitro. Fungicide suspensions were added to malt extract agar media at 0.0, 0.5,50 and 250mg a.i.l-1. A Keyworth Isolator plug cutter, 1mm diameter, replacing one objective lens of a light microscope, was used to cut cylindrical plugs of agar bearing one germinated conidium of the target fungi. Plugs were lifted out with a sterile needle and transferred onto fungicide-treated media and incubated in the dark, at 27¢ªC for 48 hours, after which the mycelial growth was assessed. Single spore isolates and parent cultures of both pathogens demonstrated significant variation in sensitivity to benzimidazole fungicides both between single spore isolates themselves, and between them and their parent cultures. It is concluded that there is a definite advantage in using a number of single spore isolates in addition to observations on multi-spored or gross mycelial isolates in any screening for chemical sensitivity in such rapidly growing and rapidly sporulating fungi in order to get early warning of insensitive forms in the population".
Utilisation of immunochemical methods for the assessment of potato leaves resistance to Phytophthora infestans
I. Kudlíková, J. Chalupníková and J. Krátká
Research Institute of Crop Production, Division of Plant Medicine, Drnovská 507, Prague, Czech Republic
In many countries, late blight caused by the fungus Phytophthora infestans (Mont.) De Bary is considered to be the most important potato disease. The most substantial part of integrated pest management for late blight in potato is breeding for resistance. In breeding programmes, the precise quantification of pathogen in host organs is essential. For that reason, a method of assessment on the base of immunochemical techniques was developed and applied in the comparison of potato cultivar resistance. Antigen was purified as a protein fraction from mycelium of four Phytophthora infestans isolates. Two polyclonal antibodies were prepared, characterised and applied in the detection of the pathogen in artificially infected leaves of ten potato cultivars (Vera, Kordoba, Lenka, Adéla, Impala, Filea, Liseta, Arnika, Rosella, and Désirée). PTA-ELISA and dot-blot on nitrocellulose membrane were used to prove the presence of the pathogen and quantify its proteins in plant tissue. The level of resistance was determined for each cultivar on the base of calculated total amount of pathogen proteins in all leaves and of the number of leaves assessed as positive. The differences in susceptibility among tested cultivars were evaluated. Cultivars Arnika, Rosella and Désirée appeared as the most susceptible according to the both criteria. Likewise, cultivar Lenka was assessed as the most resistant according to the both criteria. On the base of the amount of pathogen proteins, continuous range of resistance among tested cultivars was observed from the most resistant Lenka to the most susceptible Arnika (Lenka Liseta, Filea, Impala, Kordoba, Vera, Adéla, Désirée, Rosella, and Arnika). Results also demonstrated that the evaluation of resistance by visual symptoms did not always correlate with the amount of the pathogen in host plant tissue. Cultivar Désirée was a typical case. It showed a hypersensitive reaction without sporulation of pathogen but according to the amount of pathogen proteins in host tissue it was classified as a highly susceptible cultivar. This study was supported by the Ministry of Agriculture of the Czech Republic, projects No. QC 1301.