Barley (Hordeum vulgare) is the fourth largest cereal crop in the world with annual grain production averaging between 130 and 150 million tonnes. The majority of production is used as animal feed with consumption for malting accounting for approximately 20% of the annual production (FAOSTATS).
Barley is cultivated over a wide range of environmental conditions ranging from spring sowing in extreme latitudes or altitudes to autumn sowing in sub-tropical regions. This diversity of environments reflects barley’s tolerance of different environmental conditions as it is recognized as being more drought and salt tolerant than wheat. Barley has spring and winter crop growth habits with the latter requiring a period of cold-chilling (vernalisation) to induce flowering. The winter crop tends to be higher yielding but needs to have sufficient cold hardiness in regions where very low winter temperatures occur regularly.
Barley can also be differentiated by the numbers of rows of grains found on each ear. Barley flowers are formed on the rachis, a terminal section of the stem with many small sections separated by nodes. Each barley rachis node carries three uni-floreted spikelets with only the middle floret being fertile in the two-rowed form and all three fertile in the six-rowed form. Six-rowed barley is potentially higher yielding, especially in regions where the tillering capacity of the plant is limited, but it tends to produce a more diverse grain sample and thus can present problems in malting so maltsters generally prefer to use the two-rowed form.
Adaptation to macro environments is achieved by the selection of cultivars that have the right balance of vernalisation requirement, photoperiod sensitivity and other genes affecting flowering time. Selection within these environments is for the right balance of yield, end-use quality, and disease resistance characteristics.