Soybean Yield Formation Physiology - A Foundation for Precision Breeding Based Improvement

Abstract

The continued improvement of crop yield is a fundamental driver in agriculture and is the goal of both plant breeders and researchers. Plant breeders have been remarkably successful in improving crop yield, as demonstrated by the continued release of varieties with improved yield potential. This has largely been accomplished through performance-based selection, without specific knowledge of the molecular mechanisms underpinning these improvements. Insight into molecular mechanisms has been provided by plant molecular, genetic, and biochemical research through elucidation of the function of genes and pathways that underlie many of the physiological processes that contribute to yield potential. Despite this knowledge, the impact of most genes and pathways on yield components have not been tested in key crops or in a field environment for yield assessment. This gap is difficult to bridge, but field-based physiological knowledge offers a starting point for leveraging molecular targets to successfully apply precision breeding technologies such as genome editing. A better understanding of both the molecular mechanisms underlying crop yield physiology and yield limiting processes under field conditions is essential for elucidating which combinations of favorable alleles are required for yield improvement. Consequently, one goal in plant biology should be to more fully integrate crop physiology, breeding, genetics, and molecular knowledge to identify impactful precision breeding targets for relevant yield traits. The foundation for this is an understanding of yield formation physiology. Here, using soybean as an example, we provide a top-down review of yield physiology, starting with the fact that yield is derived from a population of plants growing together in a community. We review yield and yield-related components to provide a basic overview of yield physiology, synthesizing these concepts to highlight how such knowledge can be leveraged for soybean improvement. Using genome editing as an example, we discuss why multiple disciplines must be brought together to fully realize the promise of precision breeding-based crop improvement.

Keywords: crop growth rate; duration of flowering; genome editing; leaf area duration; precision breeding; seed filling period; soybean; yield.

FIGURE 1

Average global soybean yield over time. Data for average historic global soybean yield was sourced from the UN Food and Agriculture Organization (FAO) database in September 2021 (http://www.fao.org/faostat/en/#data). The figure depicts average soybean yield over time and a regression line was plotted for reference.

FIGURE 2

Total soybean biomass accumulation over developmental time overlain with the critical periods for yield formation. This figure represents the general accumulation of soybean biomass accumulated in all parts of the plant over developmental time, adapted from data described by Pederson and Licht (2014). (A) Critical periods for node, pod, seed number and seed weight are indicated. (B) Yield-related components are indicated during the developmental times at which they are most relevant for yield formation.

FIGURE 3

An illustration of the relationship of seed number and seed size to soybean yield. Linear correlations were derived between yield, seed number, and seed size to depict the more significant relationship to yield for (A) seed number as compared to (B) seed mass. In this example, 40 soybean lines adapted to the Midwest US were grown in replicated field plots at seven locations across Illinois, Indiana, and Missouri (Uniform Soybean Tests: Northern Region 2019; Uniform Test III – Treated Material; https://purr.purdue.edu/publications/3416/1). Seed number per unit area was calculated based on average yield per location divided by average seed size (Nowling and Guohong, 2019).

FIGURE 4

Relationship between soybean yield components and yield. The graphical and mathematical relationship between soybean yield components and final yield on a per unit area measurement.

FIGURE 5

Soybean yield-related components. The basic definitions for soybean yield-related components.

FIGURE 6

Relationship between soybean yield-related components and yield. The mathematical relationship between soybean yield-related components and final yield on a per unit area measurement.