Phenological development in relation to thermal units tn sunflower

A field experiment was conducted during rabi season, 1995 at research farm of Chaudhary Charan Singh, Haryana Agricultural University, Hisar to study the sunflower development in relation to growing degree days (GDD). Two sun flower genotypes namely, 'HS-1' and 'Morden' were sown in sandy loam soil o n 24th September, 1995 and 24th October, 1995. The growing degree days were computed using 5 degrees C base temperature for different phenophases of s unflower genotypes. The GDD required for vegetative emergence, vegetative s tage and reproductive stage by HS-1 genotype were 149.5, 463.4 and 761.7 da y degrees C, respectively. The corresponding values for 'Morden' genotype w ere 103.9, 470.4 and 585.3 days degrees C, respectively. HS-1 genotype requ ired 215 days degrees C more GDD to complete its growth cycle. The days tak en for occurrence of different phenotypes were correlated with GDD in both the genotypes. The regression models are as under: Y-1 = 0.0771 x 1.001(GDD) x GDD(0.8909) (R-2 = 0.9992) Y-2 = 2.428 + 0.0304GDD + 0.0000314 GDD(2) (R-2 = 0.9993) Where Y-1 and Y-2 are the days of occurrence for different phenophases in H S-1 and Morden genotypes,respectively. On the basis of these studies, it wa s concluded that these models could be used for prediction of development o f sunflower grown in semi-arid region.