Grain Yield in Two Contrasting Varieties of Spring Wheat

Abstract

To investigate factors determining grain yield in spring wheat two contrasting varieties of high (Jufy I) and low (Peko) yielding capacity were grown in field and glasshouse experiments. In a field trial Jufy I yielded approximately 14 per cent more grain than Peko on both control and nitrogen-treated plots. In another field trial employing small plots, although for both varieties doubling the seed-rate did not affect grain yield, the two varieties differed in their response to the increase in density. In Peko the yield level remained unaffected because doubling the seed-rate halved the number of fertile tillers per plant, whereas for Jufy I in addition to a shift in tiller number per plant there were changes in the number of grains per ear. In both varieties the weight per seed remained constant. When the two varieties were grown alone or as a 1: 1 mixture at the same seed-rate the grain yields were similar. In the mixture, Peko, compared with Jufy I, produced a greater number of fertile tillers and consequently a greater contribution to the total grain yield. In glasshouse experiments the grain yield per tiller and the order of leaf area duration per tiller for the period from ear emergence to grain ripening were both higher for Jufy I. On the other hand, there was no varietal difference for the net assimilation rate estimated during the vegetative phase, but excluding the roots. Additional nitrogen primarily stimulated tiller production in both varieties. Shading either the upper or lower parts of the plant demonstrated that the ear and flag leaf and its sheath are important sources of assimilates for grain formation, whereas the lower parts are relatively unimportant in this respect. There were indications that the response between varieties differed.