Physiological bases of yield and yielding ability of four wheat cultivars (Triticum aestivum L. emthell) under tropical rainfed-lowland condition [Philippines].

Four wheat cultivars (Triticum aestivum L. emthell), Trigo 3, C220-5 and C213-15 were planted in Dinaig, Maguindanao [Philippines] on September 25, 1986, November 25, 1986, February 6, 1987 at 0, 40, 80, 120, 160 kg N/ha to investigate the physiological bases of their resistance to high temperature. The yield and yield components, growth and dry matter partitioning were analyzed. The effects of using time-based formula and temperature index in the calculation of growth functions were determined. There were no significant differences in grain yield among cultivars within sowing dates. The highest yield was in Trigo 3 with 1.12 t/ha and lowest in C213-15 with 0.47 t/ha. There were significant differences across sowing dates. The yield tended to decrease as sowing was delayed after September. There was a significant interaction among cultivars, N levels and sowing dates. There was a negative linear relationship between grain yield and mean temperature during the three sowing dates. There were significant positive correlation between yield and yield components. A decrease in spike length in Trigo 3 was associated with the reduction in the number of seeds per spike and 1000 grain weight when sown later (November and February). In C213-15 and C220-5, the decrease in spike, length was associated with an increase in the number of seeds/spike and 1000-grain weight. Grain filling duration was shortened but grain growth rates were higher when sowing were made after September. Higher growth rates and grain weights were observed in florets 1 and 2 than in florets 3 and 4 in all cultivars and sowing dates. There were variations in days to booting, heading and maturity. Trigo 1 and C220-5 had longer days to maturity in September than in November and February sowings. Trigo 3 and C213-15 had less variation in maturity during the three sowing dates.