**Abstract**

Fungicides have been used for over 200 years to protect plants from damage by fungi, but today fungicidal resistance is very common among potato pathogens and it is difficult to control. The best and intensively studied example is metalaxyl resistance in *Pytophthora infestans*. Causes are many to get pathogen resistance against the fungicides like intensive use or misuse of it, repeated application of same fungicides, etc. Hence, it is today's need to find out the different strategies like different cultural practices, use of bio-agents, use of green chemicals, elimination of disease source, etc. to manage this fungicidal resistance. There are also alternative ways like increasing host resistance, use of new molecules, etc. that can be adopted to reduce the risk of fungicidal resistance.

**Keywords:** fungicide, resistance, potato diseases, management, *phytophthora*

## **1. Introduction**

Development of human civilization has been closely associated with the cultivation of crops, and plant diseases have been a concern to mankind probably since plants were cultivated more than 10,000 years ago [1]. The record of severe epidemics, which threatened crops, is reported in early Greek and Roman literature in 500 BC, and in the Roman world, Robigus, the God for cereals, was worshipped to prevent crop failure. Chemical plant protection schemes were developed at the beginning of the twentieth century with copper and sulphur as antifungal agents to control downy and powdery mildews. There was the multi-billion-dollar industry that has modern fungicides belonging to various chemical classes, differing in their mode of action against pathogens and characteristics of uptake and distribution within the plant.

Later, numerous cases of fungicide resistance have occurred worldwide because of release of fungicides with several target sites (so-called multi-side inhibitors) to the market, like organomercurials, regardless of their human toxicity and environmental pollution.

Along with that, systemic fungicides are also released which were taken up by the plant and are subsequently distributed within the entire plant, protecting also newly formed tissues. Thus, these fungicides were curative and allowed to control pathogens after infection had occurred. In the progress highly specific modern fungicides,

which block only one target in the pathogen (monospecific fungicides or single-site inhibitors), were developed. Examples of single-site inhibitors are strobilurins, phenylamides and benzimidazoles, which were released to the market in the late 1970s and in the mid-1990s. Surprisingly, after 2 years, the apple scab fungus *Venturia inaequalis* and the *polyphagous* grey mould fungus *Botrytis cinerea* developed resistance against benzimidazoles. Also, in other single-site inhibitors such as the phenylamides and the strobilurins, resistant strains got developed within 2 years after the compounds, were introduced to the market and widely used.
