Medical genetics was revolutionized during the 1980s by the application of genetic mapping to locate the genes responsible for simple Mendelian diseases. Most diseases and traits, however, do not follow simple inheritance patterns. Geneticists have thus begun taking up the even greater challenge of the genetic dissection of complex traits. Four major approaches have been developed: linkage analysis, allele-sharing methods, association studies, and polygenic analysis of experimental crosses. This article synthesizes the current state of the genetic dissection of complex traits—describing the methods, limitations, and recent applications to biological problems.

Genetic Dissection of Complex Traits

Heritability (H) on a progeny mean basis is frequently estimated in recurrent selection experiments for the purpose of estimating the expected progress from family selection; however, appropriate measures of precision have been developed for only a few heritability estimators. The objective of this research was to develop a measure of precision for H for certain balanced linear models. Exact confidence intervals for H were derived and are not restricted to a specific experimental design. The confidence intervals were applied to sorghum [Sorghum bicolor (L.) Moench] half-sib family data.

An exact confidence interval for heritability on a progeny mean basis

Background Quality is a powerful engine in rice value chain upgrading. However, there is no consensus on how “rice quality” should be defined and measured in the rice sector. Scope and approach We adopt a Lancasterian definition of rice quality as a bundle of intrinsic and extrinsic attributes. We then review how rice quality is (i) perceived and defined by consumers and industry stakeholders in rice value chains in Southeast and South Asia; (ii) measured and defined by food technologists; and (iii) predicted through genetics. Key findings and conclusions Consumers are heterogeneous with respect to their perceived differentiation of rice quality among regions, countries, cities, and urbanization levels. Premium quality is defined by nutritional benefits, softness and aroma in Southeast Asia, and by the physical appearance of the grains (uniformity, whiteness, slenderness), satiety, and aroma in South Asia. These trends are found to be consistent with industry perceptions and have important implications for regional and national breeding programs in terms of tailoring germplasm to regions and rice varieties to specific local market segments. Because rice is traded internationally, there is a need to standardize definitions of rice quality. However, food technologists have not reached unanimity on quality classes and measurement; routine indicators need to be complemented by descriptive profiles elicited through sensory evaluation panels. Finally, because rice quality is controlled by multiple interacting genes expressed through environmental conditions, predicting grain quality requires associating genetic information with grain quality phenotypes in different environments.

Rice quality: How is it defined by consumers, industry, food scientists, and geneticists?

The purpose of this study was to determine whether the rates of tomato seed germination under different stress and nonstress conditions were under common genetic controls by examining quantitative trait loci (QTL) affecting such traits. Seeds of BC1 progeny of a cross between a slow-germinating tomato breeding line and a rapid-germinating tomato wild accession were evaluated for germination under nonstress as well as cold, salt, and drought stress conditions. In each treatment, the most rapidly-germinating seeds were selected, grown to maturity, and subjected to molecular marker analysis. A selective genotyping approach detected between 6 and 9 QTL affecting germination rate under each of the four conditions, with a total of 14 QTL identified. Ten QTL affected germination rate under 2 or 3 conditions, which were considered germination-related common QTL. Four QTL affected germination rate only in one treatment, which were considered germination-related, condition-specific QTL . The results indicated that mostly the same QTL affected seed germination under different stress and nonstress conditions, supporting a previous suggestion that similar physiological mechanisms contribute to rapid seed germination under different conditions. Marker-assisted selection for the common QTL may result in progeny with rapid seed germinability under different conditions.

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ResearchArticle Common QTL Affect the Rate of Tomato Seed Germination under Different Stress and Nonstress Conditions

Tomato, one of the most important crops worldwide, has a high demand in the fresh fruit market and processed food industries. Despite having considerably high productivity, continuous supply as per the market demand is hard to achieve, mostly because of periodic losses occurring due to biotic as well as abiotic stresses. Although tomato is a temperate crop, it is grown in almost all the climatic zones because of widespread demand, which makes it challenge to adapt in diverse conditions. Development of tomato cultivars with enhanced abiotic stress tolerance is one of the most sustainable approaches for its successful production. In this regard, efforts are being made to understand the stress tolerance mechanism, gene discovery, and interaction of genetic and environmental factors. Several omics approaches, tools, and resources have already been developed for tomato growing. Modern sequencing technologies have greatly accelerated genomics and transcriptomics studies in tomato. These advancements facilitate Quantitative trait loci (QTL) mapping, genome-wide association studies (GWAS), and genomic selection (GS). However, limited efforts have been made in other omics branches like proteomics, metabolomics, and ionomics. Extensive cataloging of omics resources made here has highlighted the need for integration of omics approaches for efficient utilization of resources and a better understanding of the molecular mechanism. The information provided here will be helpful to understand the plant responses and the genetic regulatory networks involved in abiotic stress tolerance and efficient utilization of omics resources for tomato crop improvement.

Advances in Omics Approaches for Abiotic Stress Tolerance in Tomato

Seed vigor is an important seed quality trait in rice (Oryza sativa L.) that profoundly affects seedling morphogenesis in different environments. Generally, highly vigorous seeds have many advantages in agricultural production, such as resistance to adverse stresses, rapid emergence, and yield improvement. In the present study, one germplasm collection and one recombinant inbred line (RIL) population were used to identify quantitative trait loci (QTLs) for seed vigor. A total of 19 single nucleotide polymorphisms (SNPs) were found to be significantly associated with seed vigor (−log10(P) > 6) in the germplasm collection, which consisted of 200 rice cultivars. Nine loci responsible for seed vigor were identified via QTL mapping by using a high-density bin map. To screen the candidate genes more efficiently, we selected six loci that were co-localized in GWAS and QTL mapping, overlapped previous reports, repeat detected across two seasons, or high contribution rate as reliable loci. A total of 44 differentially expressed genes were obtained from the reliable loci via gene expression profile analysis. Among these 44 genes, Os06g0108600, Os06g0110200, Os06g0253100, Os06g0282000, Os07g0583600, Os07g0592600, and Os09g0432300 were the most promising candidates associated with seed vigor.

Integrating GWAS, QTL, mapping and RNA-seq to identify candidate genes for seed vigor in rice (Oryza sativa L.)

Seed germination and early seedling growth are important agricultural traits for developing populations of both irrigated and directly seeded rice (DSR). To investigate the genetic mechanisms underlying seed germination and early seedling growth in rice, 275 recombinant inbred lines (RILs) were genotyped in this study via the genotyping-by-sequencing (GBS) approach to construct a high-density linkage bin map based on the parent-independent genotyping method. Quantitative trait loci (QTLs) for 12 traits related to seed germination and early seedling growth were analyzed. Totally, 22 additive loci were detected, after analysis of the interaction between additive QTLs and environments, five stable additive loci were obtained. Among them, loci 4, 5, 12 and 14 exhibited clear pleiotropic effects that were associated with multiple traits. Analysis of the effects of the five additive stable loci showed that a single locus increased the corresponding phenotypic value. Ten of the 275 RILs pyramided the excellent alleles of the five stable genetic loci. Most phenotypic values of the ten RILs were greater than the average values. Four RILs (G260, G342, G371, and G401) with more excellent phenotypic values were subsequently selected; these RILs could serve as donor parents of favorable alleles in the breeding process. Due to the existence of pleiotropy, the use of these genetic loci for pyramid breeding can further increase the efficiency to reach breeding goals. In addition, these five stable loci have an average physical interval of only 170 kb, we also further identified five promising candidate genes by qRT-PCR, which provides us with a basis for future cloning of these genes. Overall, this work will help broaden our understanding of the genetic control of seed germination and early seedling growth, and this study provides both a good theoretical basis and a new genetic resource for the breeding of direct-seeded rice.

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Quantitative Trait Locus Analysis of Seed Germination and Early Seedling Growth in Rice.

Physical appearance and eating and cooking qualities (ECQ) encompassed in rice quality traits have pivotal roles in the new varieties approved, dictating market value. In this regard, it was increasingly important to evaluate various physiological mechanisms, physicochemical properties and the genetic basis involved in controlling grain quality. The investigation in this study showed a large variation in the phenotypic diversity of grain appearance and ECQ among 48 rice accessions. A significant correlation was observed between RVA-pasting properties and multiple grain-quality properties, and attributes of Setback (SB) and consistency (Cons) service as the primary keys in starch pasting. Grain-filling characteristics were surveyed and the principal differences of the trends of rice grain filling were found. The filling rate and duration exhibited significant influence on grain quality. Significant marker-trait association for grain shape, chalkiness and ECQ were explored integrally, proving optional valuable loci can be used for alleles pyramiding. Three SNP markers, GBSSI-G/T, GBSSI-4-IF and SSIIa-GC/TT, can straightforwardly be used for polygenic pyramiding by carrying alleles of T/T, C/C and TT/TT, satisfying for genotype selection for ECQ properties of low-AC, high-GC, and low-GT.

Jing Yang

Papers

Integrating GWAS, QTL, mapping and RNA-seq to identify candidate genes for seed vigor in rice (Oryza sativa L.)

Quantitative Trait Locus Analysis of Seed Germination and Early Seedling Growth in Rice.

Pasting properties, grain-filling characteristics and allelic variation linked to the grain quality in diverse rice