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Drought resistance in wheat

P.M. Bremner

CSIRO, Division of Plant Industry, P.O. Box 1600, Canberra City, A.C.T. 3601.

Among the various studies of crop water relations being pursued within the CSIRO Division of Plant Industry is one concerned with the field screening of wheat cultivars for their performance in drought. This programme utilizes an automatic raincover facility comprising twelve covers each of which may protect a number of microplots (1.5 - 2.3 m3). Water extraction is monitored (to a depth of 160 cm) by neutron meter, there being an access tube in each microplot. Cultivars are assessed in a single drying cycle commencing after plants are established and tillering has begun, i.e., the field regime simulated is one where plants rely largely on stored water. The main criteria in cultivar evaluation are 'whole season' performance in terms of total dry matter production (TDM), water used (WU), water use efficiency - TDM/WU - (WUE), and grain yield (Y). We have concentrated on comparison of cultivars selected in environments which differ markedly with respect to water supply, namely Australian (e.g. 'Gabo') and Mexican (e.g. 'Pitic').

Some results from the most recent experiment are given in Table 1. These are somewhat atypical of the series as a whole in that yields were relatively high in consequence of a large soil water store, a late start to plot protection (6 weeks before anthesis) and a low evaporative demand during much of the pre-anthesis period. Nonetheless water stress was such as to produce mid-day leaf water potentials of about 30 bars at anthesis, and to reduce mean grain yield to 3.9 t/ha compared with 4.9 t/ha in unprotected plots.

TABLE 1. Crop and Water Use Data for a 1978 Wheat Experiment

Gultivar

TDM (g/m3)

WU (mm)

WUE (g TDM/mm)

Y(g/m2)

Gabo

734

330

3.16

270

Pitic

716

231

3.34

394

WW15

767

330

3.35

333

Tincurrin

639

335

3.85

370

SE

±35

  

±0.13

±13

WU was similar for all cultivars reflecting a recurring feature of the series in which cultivars have differed in the total amount of water extracted only when they have differed in the length of their growth periods. As regards WUE, Gabo fared no better in this experiment (or previous ones) than the Mexican cultivars selected under a vastly different water regime, while Tincurrin fared worse. Average WUE was 14% greater in the T. aestivum cultivars than in Tincurrin (T. compactum); however, because of its relatively high harvest index its grain yield was lower only by comparison with WW15. Cultivar differences in WUE in the series have been few; even cultivars which have shown a 30% difference in pot experiments have, in field test, yielded identical WUE values.

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