Required Growing Degree-Days (GDDs) for each Phenological Stage of Fritillaria imperialis

Abstract

Studying plant phenology is very important to regulate the rangeland utilization. Plant phenology can be determined by Growing Degree Days (GDDs). Since temperature varies yearly, the phenological stages may consequently differ yearly. Determining the base temperature is one of the key steps in the calculation of GDDs. The aim of this study was to calculate the required GDDs for each phenological stage to predict phenological stage of <em>Fritillaria imperialis</em> based on GDDs in the consequent years. To do so, <em>Fritillaria</em> bulbs were placed at constant temperatures of 0, 1, 2, 3 and 4^°C. The length of sprouts as a growth index was measured as a function of temperature. Plant chronology was recorded in three day intervals from March 1^st, 2016 in the field and the date of each phenological stage was recorded in the form of an index developed by combining Fick and Haun indices. Then, 20 plant individuals were selected in Dasht-e-Laleh of Kouhrang County, Iran and their growth stages were recorded. Meanwhile, the required amount of accumulated GDDs (AGDDs) to reach each phenological stage was also calculated. Results showed that <em>Fritillaria imperialis </em>began the sprouting (phase E) after receiving 130.75 GDDs on March 23^rd, 2016. The emergence of leaves began on 27^th March with 166.30 GDDs and finished on 9^th April. Finally, this plant on 9^th May received 560 AGDDs and went to senescence. Based on the phenological data, when the plant received 240 AGDDs, flowering stage started. The most appropriate time for tourist entrance is in the R₂ stage (flower opening) when the plant receives 298.8 AGDDs and the best exit time is when the plant receives 359.2 AGDDs. So, the relationship between phenological stages of the plant and GDDs will be useful in visiting the site in terms of ecotourism and determining proper visit times.