Effects of planting date and plant density on phyllochron and active ingredient content in milk thistle (Silybum marianum L.)

In order to investigate the effects of planting date and plant density on phyllochron and active integradients of milk thistle (Silybum marianum L.), two field factorial experiments based on a randomized complete blocks design were carried out in two sites (Rudbar and Rasht) in Guilan province, Iran, with three planting dates (Sep., 23; Oct., 12 and Nov., 1) and three plant densities (4, 6 and 8 plant.m-2) during 2008-2009. In this experiment it was observed that phyllochron was affected by planting date and plant density and with delay in planting date (from Sep., 23 to Nov., 1), phyllochron decreased and the rate of leaf appearance increased. The highest rate of leaf appearance was obtained in Oct., 12 (8.6 and 7.7 days in Rasht and Rudbar, respectively). Phyllochron increased with increasing plant density and the lowest phyllochron and, in other words, the maximum rate of leaf appearance was obtained in Rudbar site at a plant density of 4 plant.m-2 (7.7 days). The effect of planting date on silibin content of seeds in Rudbar site was significant (maximum 1.872 mg.g.-1DW) but it wasn’t significant on silibin content in Rasht. Effect of plant density was not significant on silibin yield.ha-1 and silibin content at both sites. Results of combined analysis showed that the effect of planting date on silibin and interaction effect of site and planting date on silibin yield.ha-1 was significant. The maximum silibin yield (1.31 kg.ha-1) was obtained from Sep., 23 in Rudbar site. According to the results of this experiment, although a delay in planting enhanced the rate of leaf appearance and increased plant's readiness to over-wintering, but it had no increasing effect on silibin content of seeds.