Biomass, yield, and related terms
Biomass, production / productivity, yield, crop performance are alternatively used in the literature. The latter term seems to account for the fitness component of a crop (cultivars etc) with production levels according to specific environmental conditions and cultural practices.
the total mass of living matter within a given unit of environmental area .
Weight or total quantity of living organisms of one animal or plant species (species biomass) or of all the species in the community (community biomass), commonly referred to a unit area or volume of the habitat .
Cellular and physiological components
Cell expansion :
a massive enlargement of the plant cell wall, suggesting that organ size could be regulated by controlling wall extensibility and the formation of novel cell wall components. In plants sometimes accompanied by an increase in ploidy due to endoreduplication.
Cell proliferation :
an increase in the number of cells as a result of cell growth and cell division.
Growth rate :
the speed at which the number of cells or organ size in an organism increases.
The increase in size (biomass) per unit of time ; maximal growth rate is represented by mmax = [ln(Mt/M0)/t], where M = mass (g) and t = time (days).
Eco-evolutionary studies have viewed growth rate variation from the perspective of environmentally driven life-history trade-offs and corresponding fitness gain.
Molecular biologists have primarily implicated variation in molecular-level mechanisms, such as the genetic regulators of protein synthesis, as explanations for variation in growth phenotypes.
Intrinsic yield gene (IYG) 
Gene that when modified improves plant growth and yield under standard conditions.
The genetic and molecular bases of yield traits is based on phenotype to genotype hierarchy approaches .
Top-down approaches use quantitative trait locus and linkage disequilibrium mapping, start with a phenotype of interest and use genetic analysis to identify candidate genes.
Phenotype – QTL analysis, association or LD mapping, candidate genes, population genetics, signature of adaptation.
Bottom-up approaches use population genetic analyses to identify potentially adaptive genes and then rely on standard bioinformatics and reverse genetic tools to connect selected genes to a phenotype.
Metabolite profile :
the metabolic complement (metabolite pool) of a cell, tissue or organism under a given set of conditions.
RNA:DNA ratio :
a nucleic acid index used extensively as a measure of physiological and nutritional state ; often used as a surrogate for growth rate .
Yield (mainly associated with crops)
Yield is the biomass in an area at a given moment of the standing crop. Fresh (fw) and dry (dw) weight express the amount of produced biomass. Secondary metabolites and various bio(active)molecules are expressed as % of fw or dw.
Yield potential is defined as the yield of a cultivar when grown in environments to which it is adapted, with nutrients and water non-limiting and with pests, diseases, weeds, lodging, and other stresses effectively controlled. As such, it is distinguished from potential yield, which is defined as the maximum yield that could be reached by a crop in given environments .
It is estimated that optimizing worldwide potential yields of major crops, global food production could be increased by approximately 30 to 60% under current agricultural practices and technologies .
Genetic yield potential (Y) :
the yield that a crop can attain under optimal management practices and in the absence of of biotic and abiotic stresses .
Factors of Y :
St (GJ m−2) : the total incident solar radiation across the growing season.
partitioning efficiency (εp), also termed harvest index ; the amount of the total biomass energy partitioned into the harvested portion of the crop.
light interception efficiency (εi) of photosynthetically active radiation (400–700 nm) is determined by the speed of canopy development and closure, leaf absorbance, canopy longevity, size, and architecture.
conversion efficiency (εc) the ratio of biomass energy produced over a given period to the radiative energy intercepted by the canopy over the same period (i.e. the combined gross photosynthesis of all leaves within the canopy, less all plant respiratory losses).
14 juin 2012