Temperature Effects on the Duration of the Spikelet Growth Phase and Spikelet Abortion in Barley

Above optimal temperatures in cereals, when measured in thermal time units (°Cd) can lead to underprediction of developmental events by models, particularly when cereals are sown late in Mediterranean-type environments or grown under subtropical conditions. Our objective was to assess the effects of high temperatures on the length of the spikelet growth phase, the number of spikelet nodes per spike and level of spikelet abortion in spring barley (Hordeum vulgare L.). The spikelet growth phase (from the end of the spikelet initiation phase to anthesis) of three cultivars, 'Bandulla', 'Schooner' and 'Weeah' was subjected to two temperature regimes. In the first of two sowings, the mean daily maximum temperature for one regime was 24 °C (maintained for 6 h daily) and the mean daily minimum was 8 °C (24/8 °C). The second temperature regime was 27/17 °C. Corresponding temperatures for the second sowing, which was subjected to slightly longer photoperiods, were 26/8 °C and 26/17°C, respectively. The duration of the spikelet growth phase was longer for 27/17 °C than for 24/8 °C in the first sowing when measured in calendar time (d). In the second sowing, the duration of the spikelet growth phase was slightly shorter under the higher temperature regime (d). The duration of the spikelet growth phase (in°Cd) was greatly increased by the higher temperature treatment in both sowings. In the first sowing, the percentage of aborted spikelets was greater at HT than at LT for Bandulla and Weeah at both sowing times and the duration of the spikelet growth phase increased with higher night temperatures, suggesting that length of the spikelet growth phase was not the sole factor responsible for the proportion of aborted spikelets.