The development of plant molecular genetics, quantitative genetics and associated technology like Marker Assisted Selection(MAS) has led to the emergence of a new field in plant breeding i.e., Gene pyramiding. Gene pyramiding is defined as a method aimed at assembling multiple desirable genes from multiple parents into a single genotype. Objective of gene pyramiding include enhancing trait performance by combining two or more complementary genes, remedying deficits by introgressing genes from other sources, to reduce the selection pressure and/or increasing the disease resistance and broadening the genetic base of related cultivars. In general, the development of pyramid lines is a long and costly affair in addition to the epistatic effect. However, MAS based gene pyramiding could facilitate in pyramiding of genes effectively into a single genetic background and identify the combined effects2.

 

Gene pyramiding scheme can be divided into two parts. The first part is aimed at cumulating one copy of all target genes in a single genotype (called root genotype). The second part (fixation step) is aimed at fixing the target genes into a homozygous state, that is, to derive the target genotypes from the root genotypes. To achieve this ‘high degree’ gene pyramided lines, marker assisted gene pyramiding can be employed either with backcrosses or without backcrosses1. Constructing the ‘high degree’ gene-pyramided lines has important practical implications; such lines could be used for multiple purposes, for example, as a high-powered breeding stock line or a material line for characterizing multigene interactions.

The success of gene pyramiding strategies is largely facilitated by availability of molecular markers, which are tightly linked to the gene interest. Molecular marker integrated backcross breeding program has been employed to transfer three major Bacterial Blight (BB) resistance genes (Xa21, xa13 and xa5) into Jalmagna variety of rice. During backcross generations, markers closely linked to the three genes were used to select plants possessing these resistance genes. The three-gene pyramid and two gene pyramid lines exhibited high levels of resistance against the BB pathogen4. Soybean rust resistance through pair wise gene pyramiding was successful by validating the use of marker assisted selection in F2­ and F3 families and determining the most effective gene combinations for rust resistance3. Finally, gene pyramiding is gaining considerable importance, as it would improve the efficiency of plant breeding to develop genetic stocks and precise development of broad spectrum resistance capabilities.

 

Selected references:

 

1.                     Ishii, T., Hayashi, T. and Yonezawa, K., 2008, Optimization of the marker based procedures for pyramiding genes from multiple donor lines: III. Multiple gene assemblage using background marker selection. Crop Sci., 48:2123–2131.

2.                     Joshi, N.K. and Nayak, S., 2010, Gene pyramiding-A broad spectrum technique for developing durable stress resistance in crops. Biotech. Mol. Biol. Rev., 5: 51-60.

3.                     Maphosa, M., Talwana, H. and Tukamuhabwa, P., 2012, Enhancing soybean rust resistance through Rpp2, Rpp3 and Rpp4 pair wise gene pyramiding. African J. Agril. Res., 7(30): 4271-4277.

4.                     Pradhan, S. K., Nayak, D. K., Mohanty, S., Behera, L., Barik, S. R., Pandit, E., Lenka, S. and Anandan, A., 2015, Pyramiding of three bacterial blight resistance genes for broad-spectrum resistance in deepwater rice variety, Jalmagna. Rice, 8: 19.