Crop Variety Trials

Data Management and Analysis

Weikai Yan

• Publisher: Wiley-Blackwell
• Year: 2014
• ISBN:
  9781118688564
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Agronomy
• Index: Technology & Engineering

Variety trials are an essential step in crop breeding and production. These trials are a significant investment in time and resources and inform numerous decisions from cultivar development to end-use. Crop Variety Trials: Methods and Analysis is a practical volume that provides valuable theoretical foundations as well as a guide to step-by-step implementation of effective trial methods and analysis in determining the best varieties and cultivars.

Crop Variety Trials is divided into two sections. The first section provides the reader with a sound theoretical framework of variety evaluation and trial analysis. Chapters provide insights into the theories of quantitative genetics and principles of analyzing data. The second section of the book gives the reader with a practical step-by-step guide to accurately analyzing crop variety trial data. Combined these sections provide the reader with fuller understanding of the nature of variety trials, their objectives, and user-friendly database and statistical tools that will enable them to produce accurate analysis of data.

Chapter 1
Theoretical Framework for Crop Variety Trials

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Key points

• The ultimate purpose of crop variety trials is to identify superior cultivars for a given target environment. The target environment is the sum of the environments that are likely to be encountered in a target region across years.
• The heritability of a trait obtained from a variety trial system is a measure of the system's ability to reveal any genetic differences among tested genotypes for the trait.
• Heritability is a relative measure of the genetic variance (G) versus the genotype-by-environment interaction variance (GE), ignoring any experimental errors. So G and GE must be considered simultaneously in variety evaluation.
• Heritability must be estimated in the genotype–location–year framework because superior cultivars must be identified in test environments representative of the target environment.
• Heritability estimated in the genotype–location–year framework facilitates appreciation of the relative power of a single-trial, multilocation trials in a single year, and multilocation trials in multiple years.
• Variance components constituting heritability in the genotype–location–year framework can reveal possible approaches to improve the efficiency of variety trials, which are the topics of this book.

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Variety trials are conducted every year in every geographical or administrative region for every major crop in that region. They are conducted by plant breeders to identify improved genotypes and/or by agronomists to identify superior cultivars to recommend to the growers. Despite the budget situation, variety trials are conducted every year and have rarely been discontinued, indicating their great importance to the agriculture and the economy. Variety trials are probably the best-funded applied research in agriculture.

The sole purpose of the whole book is to provide methods and techniques that can improve the efficiency of variety trials through variety trial design, conduct, data collection, data management, data analysis, and decision-making. This chapter is to set up the basic theoretical framework for crop variety trials.

The ultimate measure of the efficiency of a variety trial system is the predicted genetic gain, ΔG for a trait or trait complex. According to the quantitative genetics theory, the predicted genetic gain is determined by three factors: the selection intensity (i), the heritability of the trials (h² or H), and the square root of the phenotypic variance (σ²_p) in the trials:

(1.1)

The selection intensity is the inverse of the proportion of the selection population that is selected; a higher intensity means a smaller proportion of the genotypes are selected. It is an arbitrary value set by the researcher. The heritability is the ratio of the genotypic variance (σ²_g) over the phenotypic variance,

(1.2)

It is the proportion of the observed variation among genotypes that is due to genetic differences for the trait of interest. Therefore, the heritability may also be understood as the “relative genetic variance” or “relative genetic variability” (Hanson and Brim, 1963). Equation 1.1 can also be rewritten as

(1.3)

Since the selection intensity is an arbitrary value, and the genotypic variance or its square root is supposed to be a constant for a given set of genotypes, the sole determinant of the predicted genetic gain in the variety trials is h, i.e., the square root of heritability.

So, heritability is the single most important concept in quantitative genetics with regard to variety trials. All measures taken in varie...