Introgression of Allelopathic Traits into Drought-Tolerant MRIA1 Rice Variety through Backcross Breeding and Validation via the Relay Seeding Technique

Abstract

Backcross breeding is a widely used approach for introgressing desirable genes into elite cultivars. In rice production, weeds and drought are two major constraints that substantially reduce rice yield. Although herbicides are commonly used for weed control, their excessive application poses risks to human health, disrupts ecological balance, and promotes the evolution of herbicide-resistant weed populations. Therefore, developing rice varieties that combine allelopathic potential with drought tolerance represents a sustainable breeding strategy for reducing weed pressure while improving climate resilience. The novelty of this study lies in the marker-assisted introgression of allelopathic quantitative trait loci (QTLs) from the Bangladeshi rice cultivar BR17 into the drought-tolerant Malaysian variety MRIA1, followed by the validation of allelopathic performance using the relay-seeding technique and the development of improved allelopathic breeding lines. The experiment was conducted from March 2020 to July 2022 at Ladang 15 and the Seed Technology Laboratory, Faculty of Agriculture, Universiti Putra Malaysia. BR17 was used as the donor parent for allelopathic traits, whereas MRIA1 served as the recurrent parent because of its high yield potential and drought tolerance. Marker-assisted backcross breeding was employed to develop BC₁F₁, BC₂F₁, BC₂F₂, and BC₂F₃ populations through foreground and background selection. The selected BC₂F₂ introgression lines were subsequently evaluated for allelopathic activity to identify superior lines with enhanced weed-suppressive potential while retaining the desirable agronomic characteristics of the recurrent parent. This study successfully developed improved drought-tolerant rice lines with enhanced weed-suppressive potential, providing valuable genetic resources for breeding climate-resilient rice. These findings demonstrate the effectiveness of integrating marker-assisted backcross breeding with phenotypic validation to combine allelopathy and drought tolerance in elite rice backgrounds. The developed lines provide valuable breeding materials for developing climate-resilient, weed-competitive rice cultivars, with the potential to reduce herbicide dependence, support sustainable weed management, and improve rice productivity under changing climatic conditions.