Plant Pathology Science

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Vegetables are attacked by different pests and diseases during their growth. Some fruits such as cucumber have sprayed regularly against diseases like Pseudoperonosporacubensisspecially in humid areas, and after a short time the cucumber are picked up and the amount of pesticide residue are measured and comparing with Maximum Residue Level (MRL). In this research the amount of Mancozeb fungicide has quantified in cucumber samples in Sari district. So in this order 26 samples of cucumber are collected and were carried to the laboratory. Samples of fruits are weighted and washed by using of n- hexan in Suksoleh device. After concentrating the obtained solution put in spectrophotometer set for measuring the optical density with 280 nanometer wave lengths and the amount of uv absorbance of samples and standard solutions were checked. The obtained numbers was changed into all right amount of mancozeb by using Excel software and Cx= α. Cs / β. Vx equation. Results showed that the amount of remained mancozeb fungicide was less than maximum residue limit in 77 percent of samples and more than maximum residue limit in 23 percent of samples in these periods. Also it defined among the samples which have had residue higher than standard limit, just 2 samples have been increased more than 1 milligram per kilogram.

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Alfalfa downy mildew caused by Peronospora trifoliorum de Bary, is one of the factors decreases alfalfa yield. It distributes as epidemic and causes falling and yellowing the leaves in favorite conditions especially in spring and first cutting of alfalfa. In order to select alfalfa resistant ecotypes to downy mildew disease, standard greenhouse and field experiments can be used. In greenhouse tests 7-day-old seedlings are inoculated with spore suspension and after incubation period, the percentage of the symptomless seedlings is compared with resistant control as soon as disease symptoms appear. Field experiments are carried out with minimum three replications of alfalfa ecotypes in an appropriate statistical design at some locations in which natural condition for disease occurrence exists. A susceptible ecotype is used as spreader in order to help disease distribution. Resistance of ecotypes is evaluated based on percentage of the leaves infection in five different classes (1-5) scoring system. Nowadays large number of researches has been done on alfalfa resistance to downy mildew and several resistant cultivars have been reported worldwide. For example KS224 and Saranac have been known as resistant cultivars to downy mildew. Some cultivars and ecotypes such as Kiseverdai, Nikshahri, Gharghlooogh and Malek-Kandi show good tolerance to disease in a few researches carried out in Iran. Results of field and greenhouse experiments are relative similar and show good correlation. It seems that using these ecotypes in different regions of Iran especially cold regions in which disease is frequently observed and considering other management methods such as appropriate cutting can be considerably decrease the occurrence of the disease and the crop loss.

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Downy mildew, caused by Pseudoperonospora cubensis, is the most important disease of cucumber production in humid areas and greenhouses in Iran. The yield loss of cucumber due to downy mildew may reach to 100%. Because the chemical control is the main method of disease control, especially in susceptible cultivars, establishing a forecasting program which is based on estimation of pathogen population, recording the temperature and relative humidity of field and greenhouse, can reduce the risk of disease epidemic. So by proper application of a protective or systemic fungicide can reduce the disease incidence, production costs and the most important, the amount of fungicide residue.