野生ダイズ染色体断片置換系統群を用いたダイズの重要農業形質の遺伝解析

この博士論文は内容の要約のみの公開（または一部非公開）になっています筑波大学 (University of Tsukuba)201

Root attributes governing drought stress adaptation and the associated molecular markers in chromosome segment substitution lines in rice (Oryza sativa L.)

The wild relatives of cultivated rice offer crucial resistance genes for combating stresses like drought. Developing rice varieties with drought tolerance is possible through chromosome segment substitution lines (CSSLs), which blend the genetic background of a high-yielding parent with specific chromosome segments from a donor parent. This study aimed to study the effect of drought stress on various root traits of chromosome segment substitution lines (CSSLs) and their relationship with specific molecular markers. Ninety-six genotypes, including 80 chromosome segment substitution lines (Curinga x O. rufipogon and Curinga x O. meridionalis), 9 New Rice for Africa (NERICAs) and 7 controls were grown in Basket and PVC pipe methods for phenotyping different root traits. Under drought stress (DS), MER16, MER20, RUF10, RUF16, RUF44, NERICA1, and NERICA3 showed superior performance for most of the root traits. These evaluations were supplemented with association analysis of 17 root trait-linked simple sequence repeat (SSR) markers with root phenotypic traits. The marker RM201 is strongly associated with multiple root traits, found to be independent of three growth conditions (well-watered “WW” under Basket, WW condition and DS conditions under PVC pipe). The marker RM316 is associated with root volume, and the marker RM7424 and RM1054 show maximum root length. In conclusion, these markers can be used in marker-assisted breeding programs, and the lines carrying them can be used as parental lines in variety-development programs for drought tolerance

Identification of rice chromosome segment substitution line Z322-1-10 and mapping QTLs for agronomic traits from the F₃ population

Chromosome segment substitution lines (CSSLs) are powerful tools to combine naturally occurring genetic variants with favorable alleles in the same genetic backgrounds of elite cultivars. An elite CSSL Z322-1-10 was identified from advanced backcrosses between a japonica cultivar Nipponbare and an elite indica restorer Xihui 18 by SSR marker-assisted selection (MAS). The Z322-1-10 line carries five substitution segments distributed on chromosomes 1, 2, 5, 6 and 10 with an average length of 4.80 Mb. Spikilets per panicle, 1000-grain weight, grain length in the Z322-1-10 line are significantly higher than those in Nipponbare. Quantitative trait loci (QTLs) were identified and mapped for nine agronomic traits in an F3 population derived from the cross between Nipponbare and Z322-1-10 using the restricted maximum likelihood (REML) method in the HPMIXED procedure of SAS. We detected 13 QTLs whose effect ranging from 2.45% to 44.17% in terms of phenotypic variance explained. Of the 13 loci detected, three are major QTL (qGL1, qGW5-1 and qRLW5-1) and they explain 34.68%, 44.17% and 33.05% of the phenotypic variance. The qGL1 locus controls grain length with a typical Mendelian dominance inheritance of 3:1 ratio for long grain to short grain. The already cloned QTL qGW5-1 is linked with a minor QTL for grain width qGW5-2 (13.01%) in the same substitution segment. Similarly, the previously reported qRLW5-1 is also linked with a minor QTL qRLW5-2. Not only the study is important for fine mapping and cloning of the gene qGL1, but also has a great potential for molecular breeding

Identification and Validation of QTLs for Yield and Yield Components under Long-Term Salt Stress Using IR64 CSSLs in the Genetic Background of Koshihikari and Their Backcross Progenies

Unraveling the complex genetic bases and mechanisms underlying salt tolerance is of great importance for developing salt-tolerant varieties. In this study, we evaluated 42 chromosome segment substitution lines (CSSLs) carrying chromosome segments from IR64 on the genetic background of Koshihikari under salt stress. Two CSSLs, SL2007 and SL2038, produced higher plant dry weight and grain yield than did Koshihikari under the stress condition. These CSSLs also showed lower Na+ and Cl- accumulation in the leaf and whole plant at the full heading stage, which might be related to the higher grain yield and yield components. To understand the genetic control of its grain yield and yield components, a SL2007/Koshihikari F-2 population was generated for quantitative trait locus (QTL) analysis. Six QTLs for grain yield and yield-related traits were detected on chromosome 2. Using near-isogenic lines (NILs) from a SL2007/Koshihikari F-5 population, qSTGY2.2 was delimited to a 2.5 Mb region and novel qSTPN2 was delimited to a 0.6 Mb region. We also detected a novel QTL, qSTGF2, for grain filling, which was considered an important contributor to grain yield under salt stress in this CSSL. Our results provide insights into mechanisms conferring grain yield under salinity stress and new genetic resources for cloning and breeding

Detection of elevated CO2 responsive QTLs for yield and its components in rice

A mapping population of IR24 (indica) chromosome segment substitution lines (CSSLs) in Asominori (japonica) background was used to detect quantitative trait loci (QTLs) for response to elevated CO2 in yield and its components of rice in free air CO2 enrichment (FACE, atmospheric CO2 plus 200 ìmol CO2• mol-1) and natural atmospheric CO2 (Ambient) conditions. Transgressive segregation and continuous distribution in the CSSLs were observed for elevated CO2 response values (the value in FACE minus that in Ambient), in panicle number per plant (PN), grain number per panicle (GN), 1000 grain weight (GW) and yield per plant (YD), suggesting that all the tested traits responding to elevated CO2 were quantitatively inherited. Three (qYD-1, qYD-10, qYD-12), two (qPN-5, qPN-10) and one (qGN-1) QTLs were detected for CO2 response to YD, PN and GN, respectively, but non-QTL for GW. Interestingly, both qYD-1 and qGN-1 were located at the same marker interval of C112-C2340, on chromosome 1, and had all positive response values from IR24. The results might be useful for understanding the genetic basis for responding to elevated CO2 and breeding new rice varieties adapted to the higher atmospheric CO2environment in the future

ハイノRNAノアンテイセイニシテンヲオイタイネノシュシジュミョウニカンスルケンキュウ

博士（農学）東京農工大

Discerning combining ability loci for divergent environments using chromosome segment substitution lines (CSSLs) in pearl millet

Pearl millet is an important crop for arid and semi-arid regions of the world. Genomic regions associated with combining ability for yield-related traits under irrigated and drought conditions are useful in heterosis breeding programs. Chromosome segment substitution lines (CSSLs) are excellent genetic resources for precise QTL mapping and identifying naturally occurring favorable alleles. In the present study, testcross hybrid populations of 85 CSSLs were evaluated for 15 grain and stover yield-related traits for summer and wet seasons under irrigated control (CN) and moisture stress (MS) conditions. General combining ability (GCA) and specific combining ability (SCA) effects of all these traits were estimated and significant marker loci linked to GCA and SCA of the traits were identified. Heritability of the traits ranged from 53–94% in CN and 63–94% in MS. A total of 40 significant GCA loci and 36 significant SCA loci were identified for 14 different traits. Five QTLs (flowering time, panicle number and panicle yield linked to Xpsmp716 on LG4, flowering time and grain number per panicle with Xpsmp2076 on LG4) simultaneously controlled both GCA and SCA, demonstrating their unique genetic basis and usefulness for hybrid breeding programs. This study for the first time demonstrated the potential of a set of CSSLs for trait mapping in pearl millet. The novel combining ability loci linked with GCA and SCA values of the traits identified in this study may be useful in pearl millet hybrid and population improvement programs using marker-assisted selection (MAS)