Are antimicrobial peptides produced by members of the normal microbiota.

Bacteriocins

Explanation:

Bacteriocins are the toxic proteins that are synthesized and released by the bacteria that are the part of the normal microbiota. These proteins have a molecular weight of 900 to 5800 Daltons. The bacterial species that release the bacteriocins are resistant against it.

Secretion of bacteriocins is an adaptive feature as these toxic proteins do not allow the growth of other strains of the same species or related species. One of the examples of bacteriocins are colicins that are released by Escherichia coli.

the last one: artificial selection/genetic engineering

plant breeding is modifying the genetic composition of the plant - but this isn't cloning (which is specifically introducing a gene into a genome). but you are artificially selecting for the phenotype that you want.

the second one is literally genetic engineering - the gene would have been cloned first and then inserted or genetically engineered into the new plant cell (the cotton).