The article about pencycuron (part 5)

The growth of the isolates was inhibited by fludioxonil and tolclofosmethyl at 1 mu-g a.i./ml and iprodione at 10 mu-g a.i./ml, but the isolates varied considerably in sensitivity to pencycuron and benomyl even at 100 mu-g a.i./ml. Benomyl, iprodione, tolclofosmethyl, and fludioxonil were evaluated for control of disease under field conditions. Table beets were inoculated with soil infested with three highly virulent isolates if R solani. In 1991, one spray of each of these fungicides at a rate of 2.2 kg formulated product per hectare was applied before or after inoculation with R solani. The experiment was repeated in 1992, except that a second spray was applied 2 wk after the first spray. In both years, all fungicide applications significantly reduced the number of infected roots. In 1991, fludioxonil applied before the inoculation of R solani reduced the incidence of infected roots from 21.8 to 3.8% and was the most effective treatment. In 1992, one spray before inoculation or two sprays of fludioxonil reduced the incidence of infected roots from 14.6 to 1.2 and 0.7%, respectively. Fungicide applications made before inoculation with R solani were more effective than those made after inoculator. Of the chemicals, pencycuron gave the best disease control. T harzianum in combination with a reduced dose of pencycuron was also effective. This technique showed that most sclerotes adhering to the tuber surface were devitalized when tubers were dipped for 20 min in a 2% solution of formaldehyde. Dusting tubers with tolclofos-methyl, or spraying them with fenpiclonil or pencycuron, gave control equal to formaldehyde, whereas a sodium hypochlorite dip was ineffective. The lack of information about the actual distribution of the pathogen in potato-producing areas led to a survey of the occurrence of the disease. Black dot symptoms were observed on roots, stems and/or tubers of the 82 potato cultivars examined in 1994. A baiting bioassay, using cuttings of potato cultivars Bintje and Urgenta, revealed the presence of the pathogen in all 37 soil samples tested, which had been collected throughout the main French potato growing areas. In vitro, growth of five C coccodes isolates recovered from diseased potatoes grown in western and southern France was severely affected by imazalil, tolchlofos-methyl and, to a lesser extent, mancozeb and thiabendazole. Conversely, iprodione, flutolanil and pencycuron were ineffective in reducing the growth of these isolates. These data indicate that C coccodes is widespread in French potato cropping areas, that currently popular cultivars are susceptible to the disease, and that at least some of the fungicides commonly applied to seed tubers are ineffective against the pathogen. The sensitivity of AG4 isolates to pencycuron was negatively correlated with the mycelial growth at high temperature. Based on such observation and high lipophilicity of pencycuron, the influence of pencycuron on the fluidity of lipid membranes of R solani was examined. The composition ratio of saturated fatty acids such as palmitic acid and stearic acid in R-C was higher than that in Rh-131. On the contrary, linoleic acid, an unsaturated fatty acid, was more abundant in Rh-131. While the fluidity of liposomes prepared with total lipids from R-C remarkably decreased by the application of pencycuron, no significant diminution of membrane fluidity was observed in liposomes from Rh-131. With artificial liposomes prepared from phosphatidylcholines commercially available, the membrane fluidity fluctuated depending on the composition of fatty acids, and the effect of pencycuron on the membrane fluidity was more significant in liposomes composed of higher ratio of saturated fatty acids. It was also found that 14C-pencycuron was bound 3 times more by liposomes that resembled R-C membrane in composition of fatty acids than those mimicked the membranes of Rh-131. 

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