Primary Epidemicological Studies Of Cucumber And Muskmelon Downy Milew

Cucumber and muskmelon downy milew were caused of the Pseudoperonospora cubensis Rostov.In this article,we used the conventional disease epidemiological method to research on the incubation period,the rule of sporulation,time Dynamic Change and spatial distribution of cucumber and muskmelon downy milew.Under the situation of natural condition,the incubation period of cucumber and muskmelon downy milew approaches to 5 days,and has no distinct difference in various species.The quantity of swarm spores which disease spot created is related to the spot day age.The ability of created swarm spore increase gradually with the age increased when the disease spot day age was 1-7 ages.But at 8-10 ages,the ability of created swarm spore reduce gradually with the disease spot day age increment.The disease spot expansion was related to the disease spot day age.The disease spot developed in 1-4～(th) day slowly,and increased less than 1cm in each day.The disease spot developed rapidly in 5-6～(th) day,and increased quantity over 1cm everyday.At the 7 day the disease spot growth became slow again,growth not enough 1cm and the disease spot no longer expanded at the 8 day.High humidity time have greatly influence on the creation of spore.In 6-8 hours,the disease spot produced the spores less,and after 10 hours the disease spot began to produces spores in a great quantity.Within 24 hour,the long of high humidity time was,the more spores were.The quantity of zoosporangium produced by cucumber downy mildew can be influence on many factors,for example light,temperature,the leaf position and so on.In the direct light,the quantity of zoosporangium was most,and the quantity in the scattered light was more than in dark.In the range of 4℃～35℃,cucumber downy mildew can produce a great quantity of zoosporangiums.This quantity is relative little under 17℃,and it is creasing beyond 17℃.It is the most suitable temperature of zoosporangium produced in 17℃～35℃.On the same conditions,the sporulation capacity was weaker in the superior fresh leaves and the inferior old leaves and strongest in the middle leaves.The zoosporangiums produced by cucumber and muskmelon downy mildew were released in dark more than in day.The quantity of zoosporangium produced by cucumber and muskmelon downy mildew was decreasing with the height.Spatial distribution pattern of cucumber and muskmelon downy milew was the aggregation pattern.The species of cucumber in Jilin province are all susceptible,but parts of species such as JINGYAN 4 and LVBAO 2 are lightly susceptible.The lesion of these species is relative small and the quantity is little.It is worthwhile to mention that the resistance of the species of MaPiHuang is weaker,and the lesions are relative more.Muskmelon downy mildew's time dynamic model is a typical "S" curve and develops rapidly.With increasing of the number of days,the disease degree increases.And a week later, disease degree is sharp deterioration.After 20 days,the disease stops developing,and disease degree is near to 100%.