What are the advantages and disadvantages of several methods in microbial breeding?

Natural breeding (direct separation and purification from nature) is simple, but the chances of obtaining excellent strains are very small.

In artificial reproduction:

Mutation breeding is actually similar to natural breeding, which is to improve the mutation rate by inducing mutation. High mutation rate but low useful mutation probability is equivalent to a little development and trouble in natural reproduction (in fact, the operator is very dangerous).

Cross breeding is much more troublesome, with high operating environment and technical requirements, but high reliability, and it is easier to combine the desired strains.

Genetic engineering or transgene is troublesome and has a high failure rate, but as long as it is successful, the result will be better and the desired shape can be made according to the requirements.

In short, each one is more troublesome than the other, and each one is easier to approach the requirements.