| Results Agronomic and yield component data are presented in Table 1. In three of the eight location years there was a highly significant yield response to nitrogen treatments. The only cultivar by fertilizer interaction that was significant at the 1% level was kernel weight at Grand Junction in 1970. The general lack of interaction significance indicated that all varieties responded similarly to nitrogen treatment. The semi-dwarfs had higher yield averages than the tall varieties (Table 1). The consistency of relative yield performance over these environments is shown in Table 2 where Chris never ranked first or second in the eight trials and Waldron ranked first or second only once. A wide range of environments was tested as pointed out by the trial means which ranged from 2472 to 6626 kg/ha. Spikes per unit area were not responsible for cultivar yield differences. Chris consistently had a high mean for this character, but was consistently low in yield. Ciano Sib was high in spikes per unit area and also had a high yield. Both Nadadores and Pitic produced low numbers of spikes per unit area but were high in yield. Trial means ranged from 82 to 204 tillers, indicating environmental response for this character. Numbers of kernels per spike appeared to account for most of the yield advantage of Pitic and Nadadores. Kernels per spike can be reduced to its two components of spikelets per spike (head size) and kernels per spikelet (floret fertility). Pitic 62 and Nadadores 63 consistently had higher values than the other three varieties for both characters. This indicates that high numbers of kernels per spike in the two high yielding semi-dwarfs is a function of both head size and floret fertility. Ciano Sib showed a small advantage over the tall cultivars for kernels per spike and this advantage was attributed almost exclusively to floret fertility. Kernel weight accounted for a large portion of Ciano Sib's yield advantage over the tall cultivars. This character was also associated with the yield advantage of Waldron over Chris. Discussion Yield differences between the tall and semi-dwarf cultivars were explained in two different ways. First, Pitic 62 and Nadadores 63 achieved their yield advantage primarily because of kernels per spike. The advantage in this characteristic was due to both head size and floret fertility. Second, Ciano Sib achieved its improved yield primarily because of high kernel weight. Floret fertility was a contributing factor of lesser importance in this cultivar. Traditionally, differences in floret fertility have been attributed primarily to environment. This study shows that some genotypes have the ability to produce greater numbers of kernels per spikelet than others over a range of environments. Spikelets per spike are also under rather rigid genetic control as evidenced by the consistency of different values for different cultivars. Kernel weight is somewhat more variable. A commonly desired yield characteristic has been tillering capacity. Our study indicates that low yielding varieties have adequate tillering potential, and tillering did not account for the increased yield in the cultivars measured. Good consistency of expression for yield components over several environments was observed in this study. This indicates that these characters are under rather rigid genetic control and yield advances should be made through breeding and selection for these characters. Literature cited BRIGGLE, L. W. and O. A. VOGEL 1968. Breeding short-stature, disease resistant wheats in the United States. Euphytica Supplement No. 1, p. 107-130. JOHNSON, V. A., J. W. SCHMIDT and W. MEKASHA 1966. Comparison of yield components and agronomic characters of four winter wheat varieties differing in plant height. Agron. J. 58: 438-441. MCNEAL, F. H,.M. A. BERG and M. G. KLAGES 1960. Evaluation of semi-dwarf selections from a spring wheat breeding program. Agron. J. 52:710-712. PORTER, K. B., I. M. ATKINS, E. E. GILMORE, K. A. LAHR and L. PASCHAL 1964. Evaluation of short stature winter wheats ( Triticum aestivum L.) for production under Texas conditions. Agron. J. 56:393-396. (Received April 12, 1972) |
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