effect of drought and plant density on yield and phonological stages of isabgol and french psyllium with using growth degree days

in order to investigate of quality and quantity yield and growing degree day (gdd) of plantago ovata and p. psyllium related to water stress and density, two experiments were conducted at the agriculture research field, tehran university, karaj, in april 2005 and 2006. the experiments were designed in factorial experiments based in randomized completely block (rcb) with three replication in which the treatments were three levels of plant density (low, medium and high density), three water stress level (severe stress, medium stress and control) and two plantago species. combined analysis results showed that water stress significantly decreased seed and biological yield. average and high density in both species significantly need fewer gdd to get maximum dry matter. in isabgul 850, 984 and 1120 gdd and in french psyllium 860, 982 and 1147 gdd need to be received 50% ripening in high, medium and control drought stress, respectively.