Spatial distribution pattern and sampling technique for grapevine downy mildew in grape seedlings under open and rain-shelter cultivations

【Objective】The objective of the study was to clarify the spatial distribution pattern and sam-pling technique of grapevine downy mildew under different cultivations.【Methods】The spatial distribu-tion pattern of grapevine downy mildew in each epidemic period under different cultivations was deter-mined by five spatial distribution pattern indices. The assembling reasons were analyzed using Taylor'sregression model(1961) and Iwao's regression equation(1971). The optimal sampling number and se-quential sampling table were calculated using Iwao's method.【Results】The spatial distribution pattern ofgrapevine downy mildew was random distribution in exponential phase under open cultivation,and trans-formed into aggregated distribution in logistic phase,finally transformed into evenness distribution in de-cline phase. The spatial distribution pattern of grapevine downy mildew took on aggregated distribution inthe whole growing season under rain-shelter cultivation. The individuals of the diseased plants attractedeach other,the spatial distribution pattern of grapevine downy mildew took on aggregated distribution,and the aggregation intensity increased with increasing plant density from exponential phase to logisticphase under different cultivations. With the increasing of plant density from logistic phase to declinephase,the individual colonies were changed from aggregated distribution into evenness distribution underopen air cultivation,but the individual colonies still took on aggregated distribution under rain-sheltercultivation. The reason for the aggregation in logistic phase may be due to the biological characteristics ofthe pathogen and some environmental factors. The optimal sampling number and sequential sampling ta-ble were calculated under different densities of the disease. The optimal sampling number under differentseverity of the disease was calculated. The sample number negatively decreased with the pathogen indicesincreasing. The sequency sampling procedure under open cultivation was based on the equation;The se-quency sampling procedure under rain-shelter cultivation was based on the equation.【Conclusion】Therewas a significant different spatial distribution pattern between open and rain- shelter cultivation,thecauses of difference were compared and analyzed. The optimal sampling method in each epidemic period,the optimal sampling number and sequential sampling were determined under different cultivations.