Resistance benzimidazole

Incubation of free-living stages of the parasite in drug can be very useful, the classical example being the egg hatch test for benzimidazole resistance in nematodes (see Coles et a ., 1992). As eggs of Fasciola are killed by... 

Prichard [15] has shown that thiabendazole inhibits the NADH oxidation in the presence of fumarate in Haemonchus contortus homogenates, which are sensitive to benzimidazole derivatives. Later studies, however, in benzimidazole-resistant H. contortus [16, 17] provide contrary evidence. 

The need for new fungicides for stone fruits has increased because of the development of benzimidazole-resistant Monilinla fructicola (8,9,30) and Coccomyces hiemalls (10) in important stone fruit production areas of the eastern United States. Resistance has been a major problem for stone fruit growers because alternative fungicides are less effective, more costly or require more frequent applications than benzimidazole fungicides. The recent registrations of iprodione and triforine for control of stone fruit diseases have helped to alleviate problems caused by benzimidazole resistance. 

Ihler C F, Bjorn H 1996 Use of two in-vitro methods for detection of benzimidazole resistance in equine small strongyles. Veterinary Parasitology 65 117-125 Jacob D E, Huchinson M J, Gibbons L M 1995 Equine cyathostome infection suppression of faecal egg output with moxidectin. Veterinary Record 137 545... 

It is primarily used as a veterinary fasciolicide though it possesses activity against hookworms also. At a subcutaneous dose of 10 mg/kg, nitroxynil shows activity against adult worms of Haemonchus, Bunostomum and Oesophagostomum in cattle and sheep. It is equally effective against benzimidazole resistant H. contortus in sheep [33]. 

Mechanism of Action of jV-Phenylcarbamates in Benzimidazole-Resistant Neurospora Strains... 

Leroux and Gredt reported that benzimidazole-resistant strains of Botrytis cinerea and Penicillium expansum exhibited negatively correlated cross resistance to herbicidal N-phenylcarbamates such as barban, chlorpropham, and chlorbufam (10, 11, 12). Based on their observation, Sumitomo scientists evaluated many examples of N-phenylcarbamates to search for compounds with potent fungitoxicity and no phytotoxicity. This effort was eventually successful, leading to new fungicides such as MDPC ( , 21 ) and diethofencarb (14, 23, 24) (Figure 2). 

Diethofencarb is highly toxic to benzimidazole-resistant isolates of B. cinerea, whereas its toxicity to the benzimidazole-sensitive isolates is weak. In contrast, MBC inhibited the growth of wild type isolates at a low concentration but had low toxicity to resistant isolates. In pot tests, diethofencarb was effective for gray mold caused by resistant isolates of Botrytis cinerea, but was not effective for wild type isolates. Diethofencarb has systematic activity in plants and both preventive and curative activity in controlling gray mold. 

Table V. Amino acid substitutions of benzimidazole resistants...

However difference aspect was observed in resistance to MBC between N. crassa isolates in laboratory and B. cinerea isolates from the field. Laboratory-generated mutants of N. crassa showed various levels of resistance to MBC, and a specific one showed negatively correlated cross resistance to diethofencarb. Others showed double resistance to these chemicals. On the other hand, most of the benzimidazole resistants isolated from the field, especially in in the case of B. cinerea, were supersensitive to diethofencarb. This difference between laboratory and field strains may derive from a difference in fitness among the resistant strains of the plant pathogen. 

Most of the highly benzimidazole-resistant isolates of Venturia nashicola (the scab fungus of Japanese pear) show increased sensitivity to the Ji - phenylcarbamate compound MDPC and the jt-phenylformamidoxime compound DCPF, but the intermediately and weakly benzimidazole-resistant isolates did not. Doubly resistant isolates, i.e. highly benzimidazole-resistant isolates with the resistance to MDPC and DCPF were found. 

Some years ago, two groups of compounds, i.e. If-phenylcarbamates and N-phenylformamidoximes were synthesized in Japan and their specific antifungal activity against benzimidazole-resistant strains was reported ( 2, 3J. In France, where benzimidazole-resistant strains of the gray mold Botrvtis cinerea predominate in some areas, a N-phenylcarbamate compound diethofencarb is already in use as a mixture with a benzimidazole fungicide carbendazim. 

In the present paper, binding of carbendazim to the cell-free mycelial extracts of V. nashicola and potential interference of this binding by MDPC, DCPF or rhizoxin were examined. Antifungal activity of rhizoxin to the benzimidazole-resistant isolates of this fungus was also tested. 

Virtually all benzimidazole-resistant isolates of Penicilllum are cross-resistant to all other benzimidazole fungicides (7,8,13,14). Furthermore, many of these isolates show resistance also to the unrelated postharvest fungicides, SOPP, biphenyl, sec-butylamine, and guazatine (13,14,17,18). Multi-resistant biotypes apparently emerged from a benzimidazole-resistant population that was subjected to the selection pressure of the unrelated fungicides. 

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