Basmati rice lines development carrying multiple bacterial blight resistance genes pyramided using the marker-assisted backcross breeding approach

Basmati rice is treated as one of the world's best rice due to its extra-long grain and unique aroma,. Over the last decade, Pakistan has earned more than US$2 billion through basmati export. Unfortunately, basmati rice is being threatened with bacterial leaf blight (BLB) disease that leads to poor production and quality. We attempted pyramiding of BLB genes through marker-assisted backcross breeding using Super Basmati as the recipient and IRBB60 as the donor parent. BLB resistance genes Xa4, xa5, and Xa21 were used for introgression. Molecular markers MP1 and MP2, RM122, and pTA248 were used for Xa4, xa5, and Xa21 genes respectively for foreground selection. The 85 SSR polymorphic molecular markers were used for background selection, which showed a more than 90% recurrent parent genome recovery. Phenotypic traits for grain dimensions were also considered while selecting backcross female parents from BC1F1 to BC5F1, which resulted in saving the resources from background selection before the selfing of backcrossed lines. Multiple lines carrying BLB resistance genes combinations Xa4+xa5 and Xa4+xa5+Xa21 were developed. The BC5F4 uniform lines showed resistance against BLB disease at hotspot locations. One of the developed lines, PKBB15-116, which has a yield advantage of more than 10%, tolerant to lodging, and has basmati quality. These pyramided lines in basmati background will also be helpful for breeders to incorporate resistance genes in a shorter period of time, in order to develop new basmati rice varieties in future.