René Cortázar S.^{1}

Several hundreds wheat varieties and lines are studied every year al La Platina Exp. Sta. (INIA, Santiago), in yield trials with four replieations, and five check varieties. Plant height and yield were determined for each variety, and the effect of height on yield was studied, in 323 and 687 bread wheats, and in 303 and 322 durum wheats, in 1987 and 1988, respectively. The bread wheats were grouped in three classes, aceording to height: a) between 75 and 90; b) between 91 and 105; c) between 106 and 121 cm tall; and the durum wheats were grouped in the following c1asses: a) between 75 and 90; b) between 91 and 100; c) between 101 and 120 cm tall. The average yield determined for each group (expressed in percentage of the tests) were; fer bread wheat, in 1987: a) 88.1 %, b) 91.7, and c) 96.3; and in 1988: a) 86.7%, b) 90.9, and c) 95.2; for the durum wheats, in 1987: a) 91.1%, b) 94.4, and c) 99.2; and in 1988; a) 90.3%, b) 95.0, and c) 99.0. In all the cases, there was a significant increase in yield with plant height. On the other hand, it must be considered that taller wheats are more prone to lodging so probably the wheats in groups c) are not agronomically the best.

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^{1} Estación Experimental La Platina (INIA), Casilla 439, Correo 3, Santiago, Chile.