Optimizing Sowing and Flooding Depth for Anaerobic Germination-Tolerant Genotypes to Enhance Crop Establishment, Early Growth, and Weed Management in Dry-Seeded Rice (Oryza sativa L.)

Abstract

Poor crop establishment, high weed infestation, and consequent yield loss are major concerns for dry-seeded rice (DSR). Flooding after seeding helps in managing weeds but reduces seed germination and crop stand. Anaerobic germination (AG)-tolerant rice genotypes could overcome these problems in DSR. Screenhouse experiments were established to evaluate the effect of seed sowing depth (SD) (0.5 cm, 1 cm, and 2 cm) and flooding depth (FD) (saturated, 2 cm, and 5 cm) on crop establishment, early growth, and weed competitiveness in DSR using AG-tolerant genotypes (Khao Hlan On, Ma-Zhan Red, IR64+AG1, and IR64). Echinochloa crus-galli, Ludwigia hyssopifolia, and Cyperus difformis were used in the weedy treatment. Rice plants reached maximum emergence 9–13 days later under flooding compared with saturated conditions. Crop emergence decreased by 12–22% at 0.5 and 1 cm SD and by 48–60% at 2 cm SD, when combined with 2 or 5 cm FD compared with saturated conditions. The 2 cm SD reduced seedling emergence by 23–42% in Khao Hlan On and Ma-Zhan Red, by 62–70% in IR64+AG1, and by 90–92% in IR64 under flooding. Initial growth in rice plant height was slow under flooding but increased progressively after the seedlings emerged from water and the final height was not affected by FD. Leaf area, total shoot biomass, tiller density, and leaf number per pot of rice were higher at 1 cm SD (P< 0.05), but decreased drastically at 2 cm SD under flooding. The emergence of E. crus-galli and L. hyssopifolia decreased by 53–65% and 89–95%, respectively, but increased by 49–68% in C. difformis under 2 and 5 cm FD, respectively, compared with saturated conditions. The shoot biomass of the weeds followed the same trend. Khao Hlan On showed the highest weed-competitive ability under all FD while the biomass of IR64+AG1 and IR64 decreased by 10–14% due to weed competition under 2 cm FD. The 1 cm SD showed better growth for all genotypes under different FD. The 2 cm FD is sufficient to have a significant control of problematic weed species. The tolerance of AG of rice genotypes should be further enhanced to increase their weed-competitive ability.

Enriched-GWAS and Transcriptome Analysis to Refine and Characterize a Major QTL for Anaerobic Germination Tolerance in Rice

“…The final GWAS panel contained mainly indica accessions (329), a smaller number of aus accessions (19), and several admixed accessions (3) (Figure S3; Supplementary File S3), confirming that AG2-related genotypes exist in both sub-groups (MR and KHO are indica, while Nanhi and Kharsu are aus). Interestingly, even though the panel was highly enriched for potential MR-derived AG2 haplotypes, phenotyping revealed that most accessions were not AG tolerant.…”

“…The gene underlying this QTL was cloned as OsTPP7, a trehalose-6-phosphate phosphatase gene, which enhances anaerobic germination tolerance [16]. This QTL has been used for crop improvement and has been successfully validated in the field [17][18][19][20][21].…”

Detection and characterization of quantitative trait loci for coleoptile elongation under anaerobic conditions in rice

“…OsTPP7 is considered to be associated with starch mobilization which drives the growth kinetics of the germinating embryo and elongating the coleoptile under anaerobic conditions. In addition, a near isogenic line of qAG-9-2 showed better seedling establishment under flooding stress compared with the background variety, showing a higher grain yield in the paddy field (Chamara et al, 2018;Lal et al, 2018). In high latitude areas such as in East Asia, seedling emergence were observed under low temperature conditions in addition to flooding stress (Fukuda et al, 2014;Iwata et al, 2010).…”

Genetic Mapping by Sequencing More Precisely Detects Loci Responsible for Anaerobic Germination Tolerance in Rice

“…Additional efforts to screen more varieties had been conducted at IRRI (E. Septiningsih, unpublished data). Some of these accessions have been used for physiological and agronomical studies, and as donors in genetic studies and crop improvement efforts [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ].…”