No abstract

To improve grain yield under direct seeded and aerobic conditions, weed competitive ability of a rice genotype is a key desirable trait. Hence, understanding and dissecting weed competitive associated traits at both morphological and molecular level is important in developing weed competitive varieties. In the present investigation, the QTLs associated with weed competitive traits were identified in BC1F2:3 population derived from weed competitive accession of O. glaberrima (IRGC105187) and O. sativa cultivar IR64. The mapping population consisting of 144 segregating lines were phenotyped for 33 weed competitive associated traits under direct seeded condition. Genetic analysis of weed competitive traits carried out in BC1F2:3 population showed significant variation for the weed competitive traits and predominance of additive gene action. The population was genotyped with 81 genome wide SSR markers and a linkage map covering 1423 cM was constructed. Composite interval mapping analysis identified 72 QTLs linked to 33 weed competitive traits which were spread on the 11 chromosomes. Among 72 QTLs, 59 were found to be major QTLs (> 10% PVE). Of the 59 major QTLs, 38 had favourable allele contributed from the O. glaberrima parent. We also observed nine QTL hotspots for weed competitive traits (qWCA2a, qWCA2b, qWCA2c, qWCA3, qWCA5, qWCA7, qWCA8, qWCA9, and qWCA10) wherein several QTLs co-localised. Our study demonstrates O. glaberrima species as potential source for improvement for weed competitive traits in rice and identified QTLs hotspots associated with weed competitive traits.

The development of nutrient-use efficient rice lines is a priority amidst the changing climate and depleting resources viz., water, land, and labor for achieving sustainability in rice cultivation. Along with the traditional transplanted irrigated system of cultivation, the dry direct-seeded aerobic system is gaining ground nationwide. The root-related traits play a crucial role in nutrient acquisition, adaptation and need to be concentrated along with the yield-attributing traits. We phenotyped an association panel of 118 rice lines for seedling vigour index (SVI) traits at 14 and 21 days after sowing (DAS), root-related traits at panicle initiation (PI) stage in polythene bags under controlled aerobic condition, yield and yield-related traits under the irrigated condition at ICAR-IIRR, Hyderabad, Telangana; irrigated and aerobic conditions at ARS, Dhadesugur, Raichur, Karnataka. The panel was genotyped using simple sequence repeats (SSR) markers and genome-wide association studies were conducted for identifying marker–trait associations (MTAs). Significant correlations were recorded for root length, root dry weight with SVI, root volume at the PI stage, number of productive tillers per plant, spikelet fertility, the total number of grains per panicle with grain yield per plant under irrigated conditions, and the total number of grains per panicle with grain yield per plant under aerobic condition. The panel was divided into three sub-groups (K = 3) and correlated with the principal component analysis. The maximum number of MTAs were found on chromosomes 2, 3, and 12 with considerable phenotypic variability. Consistent MTAs were recorded for SVI traits at 14 and 21 DAS (RM25310, RM80, RM22961, RM1385), yield traits under irrigated conditions (RM2584, RM5179, RM410, RM20698, RM14753) across years at ICAR-IIRR, grain yield per plant (RM22961, RM1146) under the aerobic condition, grain yield per plant at irrigated ICAR-IIRR and SVI (RM5501), root traits at PI stage (RM2584, RM80, RM410, RM1146, RM18472). Functionally relevant genes near the MTAs through in-silico expression analysis in root and panicle tissues viz., HBF2 bZIP transcription factor, WD40 repeat-like domain, OsPILS6a auxin efflux carrier, WRKY108, OsSCP42, OsMADS80, nodulin-like domain-containing protein, amino acid transporter using various rice expression databases were identified. The identified MTAs and rice lines having high SVI traits (Langphou, TI-128, Mouli, TI-124, JBB-631-1), high yield under aerobic (Phouren, NPK-43, JBB-684, Ratnamudi, TI-112), irrigated conditions (KR-209, KR-262, Phouren, Keibi-Phou, TI-17), robust root traits like root length (MoirangPhou-Angouba, Wangoo-Phou, JBB-661, Dissi, NPK-45), root volume (Ratnachudi, KJ-221, Mow, Heimang-Phou, PUP-229) can be further employed in breeding programs for the targeted environments aimed at improving seedling vigour, yield-related traits under irrigated condition, aerobic condition as adaptability to water-saving technology.

Climate resilience is the most concentrated subject in the current scenario for rice improvement. The aerobic system of rice cultivation involving direct seeding with need-based irrigation in non-puddled soil is gaining ground with respect to a current scenario of water scarcity. The selection of lines suitable and stable under aerobic along with irrigated conditions without any yield penalty is one of the focus areas of the breeding programme for resource use efficiency. In the present study, we have screened a panel of 118 rice lines under aerobic i.e. limited water conditions and irrigated conditions at ARS Dhadesugur Karnataka to identify ideal selection indices viz. STI, TOL, SSI, YSI, YR, YI, PYR, MP and GMP for selecting the best high-yielding and stable lines under both rice cultivation methods. The deployment of selection indices here only pertains to finding the differences in yield per plant under aerobic and irrigated conditions. According to the results of multivariate analysis (correlation and PCA), STI, YI, MP and GMP exhibited a strong correlation with YP and YS. Therefore, they appear to be the most effective stress indices for the selection of lines with good yield potential under water-limited and irrigated conditions. These indices serve as valuable selection criteria for the identification of aerobic-tolerant cultivars from both water-limited and normal conditions. These indices identified lines, DB 5 (Swarna × Oryza nivara (IRGC 81848)) and NPK-40 (Swarna × Oryza nivara (IRGC81832)) wild introgression lines. GNV-14-96-1 (BPT-5204 × Nerica line) Advanced breeding line. JBB 631-1 ((Swarna*2/ IRGC 4105) (RP 5405-JBB-631-1-1-1-1-1-1)) Tropical japonica × indica introgression line. KR-209 (Wazuhophek × ISM) and KR-262 (Wazuhophek × ISM) recombinant introgression lines. TI-36 and TI-124 Ethyl Methane Sulfonate (EMS) mutants of BPT-5204. WB-10 (Langphou) and WB-16 (Phouoibi) North-Eastern Landraces were promising for both environments. These lines are suitable because of low grain yield loss under aerobic conditions and can be further considered for cultivation.