2017 ASHS Annual Conference

Abstract: Iris is one of the most economically important ornamental genera worldwide. However, most iris species and cultivars will be deciduous without any aesthetic quality as much as 5 to 6 months. Several relative iris species with similar leaf type showed evergreen and deciduous foliar habits during natural cold acclimation and de-acclimation. The objective of this study was to compare the responses of evergreen and deciduous irises to low-temperature combined with dehydration stress under controlled environment. For low-temperature and dehydration studies, uniformly sized one-year-old plants of two groups of evergreen and deciduous irises with similar leaf type, roof iris (I. tectorum) and Japanese iris (I. japonica), yellow flag (I. pseudacorus) and Louisiana iris ‘Velvet Memory’ were maintained in a growth chamber at 10 °C and 50% humidity under a 14:10 h day: night photoperiod with light intensity of 2000 lx immediately after clipped at 10 cm above the soil surface. In addition, water was withheld from plants for 0, 3, 6, 9, …, and 24 days. The results confirmed that chilling at 10 °C combined with dehydration stress could cause growth cessation in both evergreen and deciduous irises, however, deciduous ones, especially yellow flag, ceased vegetative growth much earlier than evergreen ones. Numbers of withered leaves increased significantly in Japanese iris and yellow flag, while there was no distinct increase in roof iris and ‘Velvet Memory’. Morphological variations of four irises in controlled environment were consistent with their performances during natural overwintering. Briefly, yellow flag ceased growth and fell leaves the earliest, roof iris was deciduous but had a much longer green period than yellow flag, Japanese iris and ‘Velvet Memory’ could stay green throughout the year while green leaf ratio of Japanese iris was lower than that of ‘Velvet Memory’. Shoot height was used as the growth parameter to conduct a correlation analysis with physiological and biochemical factors determined by apical shoots. Our results also confirmed that a significant negative correlation between superoxide dismutase (SOD) and shoot height among four irises. For roof iris, Japanese iris and ‘Velvet Memory’, shoot height was positively correlated with starch content and negatively correlated with abscisic acid (ABA) content, while there was no significant correlation among both factors for yellow flag. The inverse correlation in shoot height and soluble sugar content between evergreen and deciduous irises might have a great influence on their interspecific differences in growth characteristics and foliar habits.