Since the beginning of agriculture, large crop losses caused by Plant pathogenic organisms including bacteria, fungi, viruses, and nematodes have probably contributed to human hunger and malnutrition. The control of plant diseases is thus of fundamental importance for global food security issue and is a major objective of plant-breeding and pathology programs and the agricultural chemical industry during the last 100 years. The development of agrochemicals has contributed significantly to decrease crop losses, but most effective chemicals are costly and harmful to environment as well as to health of both human and animals. plant breeders have been using classical breeding methods to achieve an effective control practices from both the environmental and economic perspective, however, single disease resistance trait and pathogens rapidly evolve mechanisms became the bottleneck for the cultivation of plant with durable resistance. Only through recent molecular studies has it become apparent that identified resistance genes encode components of the plant immune system that confer the capacity to recognize and respond to specific pathogens. This molecular study can be helped to engineering a plant with durable resistance.
. During the past decade an increasing number of plant disease resistance (R) genes from different species have been identified by map-based cloning or transposon tagging approach. However, the markers used for such maps generated polymorphic data based on restriction sites (restriction fragment length polymorphism [RFLP] and amplified fragment length polymorphism [AFLP]), random sequences (random amplified polymorphic DNA [RAPD]), and repetitive elements (simple sequence repeats). Such markers may not represent the segregating gene, and the likelihood of identifying a marker linked to the target gene is a function of the distribution of the marker type and location of the gene in the genome.( Suren K et al, 2008) and become unlikely to be useful for detecting new R genes.
The recent advance in biotechnology has opened a new era for greater creativity for the breeder and germplasm by offering an effective method for creating new varieties that selectively targets a specific interested gene or a few heterologous traits. This approach provided new opportunities for accessing the great diversity of disease resistance genes in crop plants through cloning resistance genes from diverse plant species, in combination with various advances, technology A significant effort by several laboratories in the past 5-10 years has resulted in the identification and cloning of numerous R proteins from model or crops species (Chen et al. 2007. Recently, the use of PCR with degenerate primers targeted to the short conserved regions in the NBS has proven to be an efficient method for identifying resistance gene analogues (RGAs) as has been shown in many crop plants such as potato (Leister soybean, lettuce ,Arabidopsis thaliana ,Brassica spp, apple and in several other plant species. A novel molecular technique called Nucleotide Binding Site (NBS) profiling can also be used by researcher for (Van der Linden et al. 2004 specifically targets resistance genes and their analogs. NBS profiling generates a reproducible polymorphic multi-locus banding pattern and has already been successfully used to identify and map RGAs in potato, apple and lettuce (Van der Linden et al. 2004; Calenge et al. 2005; Syed et al. 2006).