The effect of sowing period on the ecophysiological response in some sunflower hybrids cultivated in the Moldavian Plain, Romania

The effect of sowing date on biochemical and physiological properties at two phenological stages (vegetative phase and anthesis) was studied on five sunflower hybrids at the Agricultural Research and Development Station of Podu-Iloaiei in 2007. Primary biosynthetic processes of sunflower hybrids were studied by cytological, biochemical and physiological determinations. The Moldavian Plain is situated in the north-eastern Romania, representing the north limit of the region favourable to sunflower growing. Experiments were conducted on two hybrid types: early hybrids P.I.2001, P.I.-2002 and P.I.-2004, created at the Agricultural Research and Development Station of Podu-Iloaiei, Iasi County, and late ones Select and Performer, created at the Research Institute for Cereals and Technical Plants, Fundulea, Bucharest. Sowing dates were April 1-16 and May 2. The special weather conditions of year 2007, studied by the average monthly values of temperature and rainfall, correlated with quantitative and qualitative values of the yield. The lack of rainfall and high night and day temperatures caused soil, air and physiological draught, decreasing yield as a result of a high percentage of undeveloped akenes. The analysis of quantitative traits showed the variation of the akene yield from 1674 kg/ha in Select hybrid to 2975 kg/ha in P.I.2001 hybrid sown early; the values were between 1732 kg/ha in P.I.2001 and 3158 kg/ha in Performer sown later. The weight of 1000 kernels of early sown cultivars was highest in Performer hybrid (72.82 g) and lowest in P.I.2001 (47.35 g); for late sown cultivars, Select hybrid (85.87 g) was highest and P.I.2002 (56.1 g) lowest.