Dynamics of tiller populations of standard height and semi-dwarf wheats

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Abstract
The effects of sowing rate and N fertiliser on tiller populations in field-sown wheat were investigated. Two cultivars were evaluated, a semi-dwarf wheat cv.“Karamu” and a standard height wheat cv.“Kopara”. The number of tillers represented in a population was related to their order of appearance, namely: main stem, Tiller 1, Tiller 2, Tiller 3, Tiller 4, and secondary tillers. The maximum rate of tiller production in the semi-dwarf exceeded 450 tillers/m2/week whereas the standard height wheat reached a rate of 390 tillers/m2Vweek. Kopara produced more tillers than the semi-dwarf but fewer survived to maturity. Maximum tiller death rates of the standard wheat exceeded 300 tillers/m2/week whereas tiller senescence was 210 tillers/m2/week in the semi-dwarf. Tiller numbers per plant were fewer at 500 plants/m2, but the increased proportion of main stems at the higher seeding rate resulted in a higher spike population because of their low mortality rate. N fertiliser at 90 kg/ha increased tiller numbers in a similar manner to a low seeding rate with Tiller 3 showing the greatest response. Tiller survival to harvest was also increased by application of N fertiliser. Tillers in Kopara were more likely to succumb to stress.