In all crops, different varieties exist with specific characteristics. There are for example rice varieties of short duration (100 days) and long duration (150 days) and there are tomato varieties with round fruits and with elongated fruits.
For many crops, there are also varieties that are resistant or tolerant for certain insects or diseases. For example there are cotton varieties that are resistant against jassids and there are onion varieties that are tolerant against attacks by thrips.
Both the use of resistant varieties and tolerant varieties can be appropriate methods to avoid crop losses by pests and diseases.
However, in the case of resistant varieties, pests or diseases may develop new biotypes which break the resistance. For example a rice variety that is first resistant against BPH becomes susceptible when this pest develops a new biotype that can survive on that variety. Pest tolerance is therefore a more durable solution.
Although resistance and tolerance against pests can be important characteristics of a variety, there are many more factors that should be considered. Depending on the area (e.g. soil type, climate), some varieties will perform better than others. Other factors that determine the choice of varieties include the taste, the size and color of fruits, etc.
As in all aspects of crop management, the farmer will have to select the proper variety for his own situation. He will have to test new varieties in his own field (first on a very small scale) to be able to observe all relevant aspects. By experimenting in his own field he will generate the information he needs. Once the farmer is well informed, he will be capable to make a better decision and to select the appropriate variety.