A marker is used in a procedure called marker assisted selection, or MAS. Indirect selection of a genetic determinant or determinants of an interest characteristic, such as productivity, disease resistance, abiotic stress tolerance, and quality, is carried out using a marker. Breeding of both plants and animals uses this mechanism. These markers are in four main categories: morphological, biochemical, cytological, DNA-based, and molecular-based markers. Marker-assisted selection is now used by plant breeders (MAS). A segment of DNA's nucleic acid, known as a marker, is arranged in a string or sequence. RNA interference (RNAi) is an effective method for understanding how genes work in plants and modifying gene expression to produce desired traits. Small RNAs produced by the plant quiet the genes of pests or pathogens that damage the plant in a process called host-induced gene silencing (HIGS), which is based on RNA interference. For experimental purposes, double stranded RNA (dsRNA) can be introduced into plant cells by agrobacterium or viruses that replicate through dsRNA. Small RNAs are typically generated by creating dsRNA in transgenic plants. To present, only viral resistance has seen commercialization of gene silencing techniques for plant pest resistance. However, by focusing on the genes crucial to these pests, HIGS has become a potential method for enhancing plant resistance to insects and nematodes. Western corn rootworm damage to transgenic maize plants expressing a dsRNA construct targeting the vacuolar H+ATPase was significantly reduced. The cytochrome P450 gene CYP6AE14's dsRNA was expressed by similarly created cotton (Gossypium hirsutum) plants, improving their resistance to bollworms. By silencing critical genes, sedentary root-knot and cyst nematodes' pathogenicity can be reduced, making the plant more resistant. Genes in these nematodes can likewise be silenced by expressing It has been shown that many genes, including those that code for neuropeptides, effector proteins that are secreted, and proteins that process RNA, are effective for this purpose. The pathogenicity of plant pathogenic fungus varies from necrotrophs like Sclerotinia sclerotiorum, which feed on dead or dying cells, to biotrophs like rusts and mildews, which invade living plant cells with haustoria. The powdery mildew fungus in cereals and Fusarium verticillioides in tobacco plants were the subjects of the first findings of HIGS-mediated resistance to fungi. Additional research has shown the effectiveness of HIGS in controlling diseases brought on by oomycete pathogens that cause lettuce downy mildew, other Fusarium species, including S. sclerotiorum, and cereal rust fungus. A wide range of genes, including those required for pathogenicity, development regulation, primary or secondary metabolism, and structural elements like chitin and ergosterol, have been shown to prevent the progression of disease when silenced. The success of HIGS silencing has also shed light on certain pathogenicity-related processes used by several fungi. For instance, the complete pathogenicity of the cereal rust fungi was demonstrated by the silencing of a gene involved in the manufacture of the plant auxin hormone IAA. Functional redundancy occurs when the byproducts of various genes can play the same job, making it difficult to inhibit a crucial activity in a disease by silencing a single gene. Since most fungal infections have a broad arsenal of effector genes, targeting one of them may not have much of an impact on pathogenicity. This is especially true when targeting genes that code for pathogenicity effectors. The technique also has the problem that RNAi typically only achieves partial silence. An important gene may not be a good candidate for engineering resistance if it can operate normally with only a small amount of the encoded protein. Finding a suitable target gene may therefore need a lot of trial and error. Therefore, it may be advantageous to use transient silencing tests that can be used to swiftly assess potential genes, particularly for plant species that are challenging to modify. The precise selection of the target sequences with no unintended effects on the host or non-target organisms, challenges in creating stably-expressing transgenic in many crops, evaluation of safety factors, and consumer resistance to transgene technology are just a few of the difficulties in commercialising HIGS as a tool in crop plants.