High grain yield is one of the most important traits requiring improvement in rice breeding programs. Consequently, the genetic basis of spikelets per panicle (SPP) and grain weight (TGW) have received much research focus because of their importance in rice yield. In this study, IL28, which is a near isogenic line (NIL) developed by introgressing chromosomal segments of the cultivar ‘Moroberekan’ into the cultivar ‘Ilpumbyeo’, showed a significant increase in the number of spikelets per panicle (SPP) and 1,000-grain weight (TGW) compared to the recurrent parent, Ilpumbyeo. Quantitative trait locus (QTL) analysis in 243 F2 plants derived from a cross between IL28 and Ilpumbyeo indicated that both qSPP6 and qTGW6 are located in the interval RM3430–RM20580. Following substitution mapping with 50 F_3:4:5 lines, qSPP6 was mapped to a 429-kb interval between RM20521 and InDel-1, while qTGW6 was mapped to a 37.85-kb interval between InDel-1 and SNP--3 based on the japonica genome sequence. This result indicates that qSPP6 and qTGW6 are different genes. Yield trials with substitution lines indicated that lines harboring the homozygous Moroberekan segment at both the qSPP6 and qTGW6 region showed significantly higher grain yield than Ilpumbyeo. Because the Moroberekan alleles for SPP and TGW have been shown to be beneficial in the genetic background of Ilpumbyeo, both the qSPP6 and qTGW6 alleles might prove valuable in improving rice yields. Closely linked SSR markers are expected to facilitate the cloning of genes that underlie these QTLs, as well as with marker-assisted selection for variation in SPP and TGW in rice breeding programs.

This study aimed to investigate the effect of nitrogen application methods on the yield and grain quality of an extremely early maturing rice variety. The experiment was conducted in the rice research field of Chungnam Agricultural Research and Extension Services, South Korea, in 2019 and 2020. Two nitrogen application methods, BD (100% as a basal dressing) and BTD (70% as a basal dressing + 30% as a top dressing), with three different nitrogen levels (70 kg/ha, 90 kg/ha, and 110 kg/ha), were employed. The results showed that BD treatment had comparable or higher head rice yields and improved grain quality compared to BTD treatment at all nitrogen levels. Additionally, the SPAD value at heading date was highly correlated with both the protein content (r² = 0.838**) and glossiness of cooked rice (r² = 0.630**). Therefore, this study suggests that BD treatment could be an effective approach to improve the productivity and quality of extremely early maturing rice varieties while saving on labor costs, and the SPAD value can be used as an index to infer the taste of rice. In conclusion, this study provides useful insights into nitrogen application methods that can be used to enhance the yield and quality of extremely early maturing rice varieties.

Developing rice varieties with increased mineral element content is the most cost-effective and efficient approach for alleviating human malnutrition and nutrient deficiencies. In this study, quantitative trait loci (QTLs) were mapped for mineral element content in 96 introgression lines derived from a cross between the elite Korean Oryza sativa japonica cultivar “Hwaseong” and the wild rice Oryza rufipogon (IRGC105491). The population was grown in two locations, and Fe, Zn, Mn, and Ca contents of the brown rice were measured. Six QTLs were identified on chromosomes 6, 8, and 10, and all O. rufipogon alleles increased trait values. The positions of qFe10 and qZn10 were further defined; higher Fe and Zn contents are related to the 375-kb O. rufipogon segment between the markers RM1873 and RM25612. The combined analysis of the whole-genome sequencing data, spatiotemporal expression profile, and gene expression suggested that a transcription factor gene, namely the rice homeobox gene 9 (LOC_Os10g33960) marks as the high potential candidate associated with Fe and/or Zn regulation. This study provides valuable information on candidate genes qFe10 and qZn10 from O. rufipogon, which may be vital in developing rice varieties with increased Fe and/or Zn content without any penalty in traits of agronomic importance.

Although silicate fertilizer has been recently recognized for its ability to suppress methane (CH₄) emissions in paddy fields, the effects of its consecutive application during the rice farming period are still a subject of debate. Moreover, while it was known that silicate fertilizer can mitigate CH₄ emissions through several electron acceptors, the effect of additional application of electron acceptors have not been extensively studied. This study evaluated the effect of silicate fertilizer with varying concentrations of iron slag on CH₄ emissions and rice yield over the 3 years rice farming period. Seasonal CH₄ fluxes exhibited a significant decrease with the application of silicate fertilizer, with the treatment containing 2.5 % iron slag showing the maximum reduction of 35 % in 2020. Additionally, in 2021 and 2022, the application of silicate fertilizer with 2.5 % iron slag resulted in a decrease of total seasonal CH₄ emission by 22 % and 23 %, respectively. Rice grain yield exhibited a significant increase with the inclusion of iron slag in the silicate fertilizer, which resulted in a 37 % and 16 % higher yield compared to no-silicate fertilization and no‑iron slag silicate fertilization, respectively. Therefore, iron slag-based silicate fertilizer could be a beneficial soil amendment to mitigate CH₄ emissions in rice paddy fields and improve rice productivity without negative effects on the atmospheric and soil ecosystem.

Yeotae Yun*, Chongtae Chung, Gyucheol Kim, and Tugsang Yun. Korean J. Breed. Sci. 2022;54:238-43. https://doi.org/10.9787/KJBS.2022.54.3.238

Yeotae Yun*, Gyucheol Kim, Giwon Cho, and Tugsang Yun. Korean J. Breed. Sci. 2022;54:305-14. https://doi.org/10.9787/KJBS.2022.54.4.305