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 u nits (degrees Cd) can lead to underprediction of developmental events by models, particularly when cereals are sown late in Mediterranean-ty pe environments or grown under subtropical conditions. Our objective w as to assess the effects of high temperatures on the length of the spi kelet growth phase, the number of spikelet nodes per spike and level o f spikelet abortion in spring barley (Hordeum vulgare L.). The spikele t growth phase (from the end of the spikelet initiation phase to anthe sis) of three cultivars, 'Bandulla', 'Schooner' and 'Weeah' was subjec ted to two temperature regimes. In the first of two sowings, the mean daily maximum temperature for one regime was 24 degrees C (maintained for 6 h daily) and the mean daily minimum was 8 degrees C (24/8 degree s C). The second temperature regime was 27/17 degrees C. Corresponding temperatures for the second sowing, which was subjected to slightly l onger photoperiods, were 26/8 degrees C and 26/17 degrees C, respectiv ely. The duration of the spikelet growth phase was longer for 27/17 de grees C than for 24/8 degrees C in the first sowing when measured in c alendar time (d). In the second sowing, the duration of the spikelet g rowth phase was slightly shorter under the higher temperature regime ( d). The duration of the spikelet growth phase (in degrees Cd) was grea tly increased by the higher temperature treatment in both sowings. In the first sowing, the percentage of aborted spikelets was greater at H T than at LT for Bandulla and Weeah at both sowing rimes and che durat ion of the spikelet growth phase increased with higher night temperatu res, suggesting chat length of the spikelet growth phase was not the s ole factor responsible for the proportion of aborted spikelets.