| The overall response of grain yield to drought stress was mainly related
to severe reductions in (a) the size of the sink and (b) the source of assimilates
in the postheading stages. The former was related to reductions in spikes/unit
area and kernels/spike. The latter resulted from senescence of the photosynthetic
tissues during the grain filling period (2, 9). In contrast, at the site
without water stress, the limiting factor to grain yield was the source
of assimilates expressed in the 1000-grain weight. The size of the sink,
represented by spikes/m2, was secondary in this case. The five top yielding cultivars were noted for their ability to avoid stress by maintaining high values for one or more yield component traits. This indicated different genotypic response and ability to drought tolerence. The bread wheat cultivars, Vanern 's', Mesabi 's' and HD-2172, depended in their grain yield on a large sink (spikes and kernels) and less on the source (1000-grain weight). In contrast, the durum cultivars, CM 18882 and Redhead 's', were less dependent on the sink but more on the source (6). These five cultivars seemed to meet the proposed criterion for drought resistance (5) of having the highest yields at the severely stressed environment, site 1, and a strong response to the more favourable environment, site 2. Literature Cited (1) BINGHAM, J. 1969. Agric. Progr. 44: 30-42. (2) FISCHER, R.A. 1973. In R.O. Slayter (ed.) Plant response to climatic factors. UNESCO, Paris. (3) GALLIGHER, J.N., P.V. BISCOE & R.K. SCOTT. 1975 J. Appl. Ecol. 12: 319-336. (4) HURD, E.A. 1971. In K.L. LARSON and J.D.- EASTIN (ed.) Drought injury and resistance in crops. CSSA Spec. Pub. No. 2. Crop Sci. Soc. Am. Madlson, Wes (5) KEIM, D.L. & W.E. KRONSTAD. 1979. Crop Sci. 19: 574-576. (6) KEIM, D.L. & W.E. KRONSTAD. 1981. Crop Sci. 21: 11-15. (7) SLAYTER, R.O. 1969. In physiological aspects of crop yield. Am. Soc. Agron. Madison, Wis. pp. 53-88. (8) THORNE, G.N. 1966. In F.L. MILTHORPE and J.D. IVINS (ed.). The growth of cereals and grasses. Butterworth, London. (9) WARDLAW, I.F. 1970. Aust. J. Biol. Sci. 23: 765-774. |
| <-- Back |