In 1990, twenty four sorghum cultivars were evaluated for yield and crop growth rate in Isfahan. A complete randomized block design with three replications was used. Planting date was June 5th, and plant density was 133000 plants per hectar. Relative growth rate and crop growth rate were calculated using the estimated dry matter accumulation based on growing degree days.
According to the total degree days from sowing to 50% flowering date and physiological maturity, the cultivars were classified to early, mid, and late maturity groups. Cultivars differed significantly for grain yield. Grain yield ranged between 5.24 to 9.35 t/h . The cultivars in mid-season maturity group had a higher yield than the other two groups. Generally, the hybrids out-yielded the pure lines by 1.64 t/h.
Crop growth rate progressively increased to a peak value at flowering stage, and then declined for all of the cultivars in the three maturity groups. Relative growth rate declined also throughout the season, the mid-season and late maturity groups of cultivars had the highest and the lowest relative and crop growth rates, respectively. In all the three groups, the highest yielding cultivars had the maximum crop growth rates at 50% flowering stage. The strong correlation between grain yield and crop growth rate revealed the effectiveness of selection for high vieidinq cultivars based on their crop growth rates.
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