Non Technical Summary
High productivity in crops has been achieved through decades of rigorous selection and breeding. Through this process, genetic variability present in these superior varieties is expected to have diminished compared to their less improved counterparts. The ability of plants to thrive under diverse environmental conditions is largely determined by the extent of the genetic variability present in those individuals. The hypothesis here is that selection for superior performance in crop species has therefore reduced the plasticity that allows plants to change their phenotypic expression depending on the effect of environmental influences. To test this hypothesis, this project will first aim to dissect the genetic architecture of this phenotypic plasticity capacity, also known as genotype by environment (G X E), by evaluating the phenotypic and genotypic variability of a diverse collection of maize hybrids grown as part of the nation-wide collaborative Maize G X E project that is part of the Genomes to Fields initiative. As part of this project, we also plan to exploit the genotypic and phenotypic variability present in a collection of maize inbred lines derived from the Iowa Stiff Stalk (BSSS) maize population. This set of diverse materials include lines derived from the BSSS population before any selection was ever applied on it, also inbreds derived from earlier cycles of selection and then finally elite lines recently derived from materials originated from this population that have undergone intense selection. Comparisons of genotypic and phenotypic variation observed in this collection of materials will provide an initial answer to our primary research questions. In addition to that, increased planting density has been identified as one of the most important agronomic factors enhancing productivity in modern maize. Another objective of this project is to determine if insensitivity to planting density is a major contributor to the ability of plants to tolerate environmental influences. For that, a subset of the BSSS derived lines will be evaluated at different planting densities. Results generated by the overall project are expected to enhance our understanding of how rigorous selection and breeding could affect the ability of plants to interact with their surroundings. Deepening our understanding of how the interaction between plants and environments is modulated will directly impact the decision making process of practical plant breeding programs.
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Goals / Objectives
Rigorous breeding processes and the deployment of modern agronomic practices have rendered modern crop varieties remarkable levels of productivity. However, the question remains if this process of selecting for superior productivity has affected the ability of these improved cultivars to consistently adapt to variable environments. The capacity of plants to acclimate to their surrounding depends mostly on the extent and nature of standing genetic variation. If selection has narrowed down the available genetic variability present in improved genotypes, it can be hypothesized that the ability of plants to withstand changing environmental conditions has been proportionally reduced in that process. A more in-depth understanding of the genetic architecture and modulation of the mechanisms controlling phenotypic plasticity, or the ability of individuals to express different phenotypes in response to the environment, also known as genotype-by-environment (GXE), is expected to provide an opportunity to better assess the effect of selection for high-productivity on the ability of specific genotypes to respond to ever-changing environmental influences.This project presented here seeks to utilize the Iowa Stiff Stalk (BSSS) maize population, one of the most influential sources of maize germplasm in North America, and derivative inbred lines to answer fundamental questions about the control and modulation of G X E in the context of a highly selected maize population. The specific hypotheses to be addressed in this project are:1. What types of genetic modulation controls G X E in a collection of diverse genotypes? What types of variants explain most of the G X E across different economical and agronomic important traits?2. Has directed artificial selection for high productivity reduced the proportion of the variation that can be explained by G X E across different traits?3. Planting density is one of the most important agronomic factors enhancing productivity in modern maize; is insensitivity to planting density a major contributor to G X E?
For the first aim of this project, we will leverage genotypic and phenotypic data currently being collected as part of the of the G2F G X E project. This set includes approximately 900 hybrids produced by crossing approximately 350 diverse inbred lines with relevant testers. These diverse inbred lines have been genotyped using reduced representation genotyping by sequencing (GBS) approaches and data is available to G2F G X E cooperators. Subsets of this diverse collection of hybrids are being evaluated in more than 45 different environments across North America in 2014 and 2015. The remaining aims will also partially leverage resources within the G2F G X E project and will contrast a collection of inbred lines derived from the BSSS population released during different eras of breeding as well as random lines from that population that have undergone no selection. The collection of lines derived from the BSSS population will be crossed by a relevant and complementary (based on heterotic patterns) tester to maximize heterosis for traits of interest. Lines will be also crossed by a second tester chosen to represent a "poor performer". The objective here is to maximize allelic differentiation among diverse lines to facility genetic evaluation. A smaller subset of specific locations that are part of the G2F G X E project will be leveraged for this portion of the project. Detailed environmental information is collected in each of these locations and will be leveraged in the analysis. Field evaluations will include assessment of productivity characteristics such as yield, grain moisture and test weight and related agronomic measurements such as stand counts, root and stalk lodging to interpret the productivity data. Also, phenological characteristics including plant height, ear height and flowering time will be measured in all plots. Detailed protocols have been developed by the G2F G X E project for consistency across locations and years and will be deployed in this project. A more in depth evaluation of ear, cob and kernel morphological characteristics will be used as a mechanism to assess plant stress caused by a dense planting treatment that will be applied to a subset of the diverse hybrids as part of this objective. This morphological evaluation will be conducted using a high-throughput phenotyping platform developed within our program using flatbed scanners and software developed through previous research collaborations.