Combining host plant resistance and herbicide tolerance for integrated management of brown planthopper and weed complexes in direct seeded rice

Brown planthopper (BPH) is a major pest of rice. Herbicide based direct-seeded rice (DSR) cultivation without constant stagnant water can reduce its population buildup. However, conventional herbicides or manual weeding can’t control the wild and weedy rice. Extensive invasion of these obnoxious weeds can attract BPH on standing crops of resistant varieties and support off-season overwintering. We screened 51 accessions of 22 O ryza species including weedy rice for BPH-resistance and imazethapyr-tolerance. Only IRGC 88828 ( O. schweinfurthiana ) was BPH-resistant, and none were tolerant to imazethapyr which indicated the scope of harnessing the complementary benefits from the two traits. Two epistatic BPH-resistance QTLs from the landrace Salkathi and a novel AHAS gene mutation conferring imazethapyr tolerance from HTM-N22 were introgressed separately in a popular rice variety Naveen. NILs with qBph4. 3+ qBph4.4 showed both antixenosis and antibiosis against BPH and were notified as first BPH resistant essentially derived varieties in India. AHAS gene introgression using linked marker RM6844 located at approximately 0.9 cM distance enabled efficient management of volunteer, wild and weedy rice besides other non- Oryza weed species through imazethapyr application. However, significant reduction of grain yield and head rice recovery was also recorded in all the introgressed lines. While combining both the traits, linkage drag at AHAS locus was circumvented using a novel selection approach against HTM-N22 allele of RM6844. Rotational cultivation of BPH-resistant NILs through transplanting and dual-improved NILs through direct seeding will enable integrated pest and weed management and minimize cultivation cost, grain admixture, insecticide use and environmental footprint in rice.