Changes in Endogenous Abscisic Acid, trans-Zeatin Riboside, Indole-3-Acetic Acid Levels and the Photosynthetic Rate during the Growth Cycle of Curcuma alismatifolia Gagnep. in Different Production Seasons

Off-season (OS) cropping of Curcuma alismatifolia Gagnep in Thailand results m a decline m plant growth and flowers quality compared to regular sea son (RS) cropping This may be due to the distinct climatic conditions in OS such as short day length, low temperature, water stress etc which induce changes in some endogenous hormones and alter plant growth and development The experiments m two cropping season (RS and OS) were conducted to examine the changes to endogenous hormones i e abscisic acid, trans-zeatin riboside and indole-3-acetic acid, during the growth cycle The result indicated that OS cropping brought about a decrease m plant height and flower quality but significantly stimulated the forma ton of rhizomes compare with RS cropping The levels of ABA m leaves, old rhizomes and old storage roots were higher and consistently increased during off-season cropping The maximum concentration of ABA was up to 2 2 mu g gDW(-1) in leaves, 1 4 mu g gDW(-1) in old rhizomes, 1 0 mu g gDW(-1) m old storage roots, 2 3 mu g gDW(-1) in inflorescence, 0 9 mu g gDW(-1) m new rhizomes, and 0 9 mu g gDW(-1) m new storage roots The levels of ABA in RS cropping were relatively constant throughout growth stages and mostly less than 0 1 mu g gDW(-1) The levels of t-ZR were also slightly higher m leaves, old rhizomes, old storage roots, inflorescence and new rhizomes in OS than RS cropping The increase of t-ZR in new rhizomes may cause the larger number of new rhizomes m OS cropping (4 8 per plant) The concentration of IAA m leaf exudates was similar between the two growth seasons except in the final stage Therefore, it could be concluded that OS conditions induced a decrease m the photosynthetic rate, and increases in ABA and t-ZR concentrations in various organs at different growth stages, leading to depressed shoot growth and an increase in rhizome numbers