Physiology of Growth, Development and Yield

Abstract

Crop growth is a dynamic process whereby the sorghum plant germinates, emerges and begins to capture solar radiation and, via photosynthesis, accumulate biomass. Interacting with its surrounding environment, the sorghum plant adapts to the various biotic and abiotic challenges on its journey towards flowering and, ultimately, seed production. We will explain the physiology of growth and yield in sorghum using a framework based on crop growth and development. The process of evolution has enabled plants to utilise a variety of timing mechanisms that regulate development, improving the chance that germination and reproduction are aligned with favourable periods of growth. Crop development is predominantly affected by photoperiod and temperature. In contrast, crop growth, which represents the biomass produced, is predominantly affected by incoming radiation. Grain yield can be defined as the product of resource capture (light, water and nitrogen), resource use efficiency and partitioning of that resource into grain. Since water limitation is the key constraint to sorghum yield globally, crop growth will be considered in the context of water-limiting and non-limiting scenarios. In the absence of water limitation, the sorghum crop is largely limited by radiation, and in this scenario, biomass accumulation is the product of intercepted radiation and its conversion efficiency, the radiation use efficiency (RUE, biomass produced per unit of radiation intercepted). When water is a limitation, biomass accumulation under drought stress becomes a function of the total amount of water used by a crop (transpiration, T) and the transpiration efficiency (TE, biomass produced per unit of water transpired). For the first time in history, we now have the tools to measure physiological traits, such as dynamic biomass growth or canopy radiation use efficiency at a high-throughput scale that can match the genomic data. These new tools will allow us to phenotype thousands of lines that breeders have previously genotyped in multi-location field trials, a pre-requisite for the unravelling of the molecular basis of complex traits via association mapping approaches. This is particularly pertinent in sorghum due to its importance as a cereal for food, feed and fuel, especially in dry-land cropping systems.