Estimation of Effect of Environmental Factors During Seed Filling Period on Seed Weight in Different Brassica Species (B. napus L., B. rapa L., B. junceae L.)

The effect of environmental factors as temperature, photothermal quotient and rainfall during seed filling period (SFP) on seed weight of different species of Brassica was studied in Gonbad during 2003–2006 growing seasons. Twenty genotypes from different species of Brassica including: five genotypes of spring B. napus, five genotypes of winter B. napus, five genotypes of B. rapa, and five genotypes of B. juncea were sown at optimum sowing date recommended for the area. In all species, there was a linear relationship between 1000- seed weight and mean air temperature, photothermal quotient and rainfall during SFP. Increase in radiation accompanied with relatively moderate temperatures during SFP, hence, increased seed weight. Each millimeter increase in rainfall during SFP increased the rate of 1000-seed weight of spring and winter rapeseeds, mustard and turnip genotypes by 0.0094, 0.0247, 0.0105 and 0.0132 g, respectively. In addition, with an each day increase in duration of SFP, 1000-seed weight of spring and winter rapeseeds, mustard and turnip genotypes increased by 0.0533, 0.1682, 0.0456 and 0.0529 g, respectively. These relationships showed that winter rapeseeds genotypes had more response to favorable environmental factors during SFP. The non-significant relationship between seed number per unit area and seed weight in different species of Brassica showed that under conditions of this study sink size did not affect seed weight, but it was affected by environmental factors during seed filling period.