Determining of chilling and heat requirements of olive cultivars growing in Fars Province is important for the selection of cultivars that will exhibit satisfactory growth and development. The purposes of this study were determining the chilling and heat requirements of olive and comparison of Utah and Positive Utah Chill unit (PCU) models for determining the chilling requirements of olive cultivars. In this regard, chilling requirement of flower buds of ‘ Fishomi’ , ‘ Dezful’ , ‘ Zard’ , ‘ Dehghan’ and ‘ Shiraz’ cultivars were determined. Cuttings of these cultivars were taken during autumn when the mean temperature fell below 12º C. Cuttings were kept at 5 º C for periods of 0, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700 and 1800 h. Results indicated that the chilling requirements of ‘ Fishomi’ , ‘ Dezful’ , ‘ Zard’ , ‘ Dehghan’ and ‘ Shiraz’ were 900, 1000, 900-1000, 1000-1100 and 900 h, respectively. Results also showed that the PCU unit model was more efficient than the Utah for estimating chilling requirements under subtropical field conditions. Heat requirements from the end of dormancy to full bloom stage of these five olive cultivars were estimated as 199. 2, 272. 1, 245. 2, 245. 2, 321 growing degree days (GDDs), respectively. It was observed that ‘ Fishomi’ had the lowest chilling requirement and ‘ Dehghan’ obtained the highest one. Hence, ‘ Fishomi’ can be recommended for cultivation in subtropical regions.

The time and duration of developmental stages (phonological events) are important in grain yield determination of wheat. The aim of this research was to study the ratio of post- to pre-anthesis duration in wheat plant and to investigate its possible association with grain yield.Eighty-one wheat cultivars were grown at research farm of Moghan College of Agriculture and Natural Resources-University of Mohaghegh Ardabili under well-watered conditions during 2010-2011 growing season. The dates of anthesis, and physiological maturity were recorded. Grain filling period (GFP) was recorded as the period from anthesis to physiological maturity. With the objective of including temperature effects on the lengths of growth phases, all developmental stages were expressed in the form of growing degree days (GDD). The ratio of post to pre anthesis duration was calculated as the amount of GDD from anthesis to maturity (GFP) divided by the amount of GDD from sowing to anthesis. Results showed that examined cultivars had significantly differences with respect to grain yield where this trait range from 293 to 746 gram per square meter. Crossed Alborz, Akbari, and Naz were the most productive cultivars whereas Shahpasand, Omid, and Sardari performed visa versa. Close association (r=0.79, P < 0.01) was found between grain yield and biological yield. In addition, grain yield correlated significantly and positively with grain number per square meter (r=0.74, P < 0.01) and with thousand-grain weight (r=0.42, P < 0.01). Large variations were found among tested cultivars with respect to thermal time from sowing to anthesis.

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 Fritillaria imperialis based on GDDs in the consequent years. To do so, Fritillaria 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 1st, 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 Fritillaria imperialis began the sprouting (phase E) after receiving 130. 75 GDDs on March 23rd, 2016. The emergence of leaves began on 27th March with 166. 30 GDDs and finished on 9th April. Finally, this plant on 9th 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.

The effect of photoperiod and growing degree days (GDD) on dry matter and dry matter partitioning in Jerusalem artichoke was investigated during 2008-09 and 2009-10. Three Jerusalem artichoke genotypes (CN-52867, JA-89 and HEL-65) were planted in 15 day-intervals between with thirteen different dates (September 20 to March 20) at Khon Kaen University, Thailand. Jerusalem artichoke genotypes responded differently to varying planting dates for harvest index, shoot dry weight, leaf area, number of tubers and tuber size. Two genotypes, CN-52867 and JA-89, were significantly more productive on the planting date of 20 September and they also performed well on planting dates of 5 October to 20 March. Plant grown in long photoperiod with a higher number of GDD produced shoot dry weight rather than greater number of harvestable tubers, while short photoperiod induced high partitioning of assimilates to harvestable tubers. Jerusalem artichoke plants grown during short photoperiod were smaller and produced larger tubers than those grown during long photoperiod. Tuber yield was relatively unchanged across planting dates. Since Jerusalem artichoke during short photoperiod had smaller plants, growing Jerusalem artichoke at higher plant population with optimum density is highly recommended to increase tuber yield. The information obtained in this study is extremely important for Jerusalem artichoke production and breeding in the tropical agro-climatic conditions such as Thailand.

The purpose of this study is predicting climate changes and investigating the effect of probable climate change on the growing degree-days in the northwest of Iran. For this purpose the climatic data of seven synoptic stations during a 25 years period (1985-2009) was collected including Oroomieh, Tabriz, Zanjan, Sanandaj, Ghazvin, Kermanshah, and Hamedan were used as the base period and thus temperature variations periods (2030-2011 and 2065-2046) through HadCM3 model was simulated. For the little power of temporal and spatial distinction of this model, its outputs were downscaled using LARS-WG software and presented under Emission Scenarios including A1B (moderate scenario), A2 (maximum or pessimistic scenario), and B1 (minimum or optimistic scenario). Calibration, verification and Performance Model with the rate of the adaption of observed data and the simulated measures through statistics, RMSE and MAE were analyzed. Finally, using the simulated temperature growing degree-day was calculated and compared under 4 Base temperature including 0° , 5° , 10° , and 15° centigrade in the basic span (1985-2009) and future span (2011-2030 and 2046-2065). The results of simulation show that temperature change in north-west areas under all three A1B, A2, and B1 scenario are increasing in the future, but the differences among these three scenarios in each period is inconsiderable. In total the most temperature increasing was detected as 0/7 centigrade in A2 scenario for 2011-2030 period and 2/3 centigrade under A1B scenario for 2046-2065 period. Generally with the temperature increasing, the amounts of growing degree-day without exception increases in review periods and under the four Base temperature. Under studied scenarios, the Bases temperature of 0° centigrade had the most and 15° centigrade had the least impressibility from climate changes, so that the most increasing in calculated degree-day measures under 0° and 15° centigrade bases in the first period to the basic scenario (1985-2009) respectively was simulated as 207/4 and 120/6 degree-day under A2 scenario and for the second period to the 752/5 and 463/5 degree-day under A1B scenario.

The geographical distribution of growing degree-days (GDDs) within Iran was studied using GIS-based maps. GDDs were calculated using daily thermal parameters (daily maximum and minimum air temperature). Based on the purpose of the study and climatic conditions of Iran, the average value of 5oC was chosen for GDD calculation. The calculations were carried out using daily weather data of 113 meteorological stations throughout Iran. The clustering of the 113 point stations’ data were achieved by using statistical models combined with a digital terrain model. The final outcomes were five GDD maps (two for start and end of heating period, one for January, one for cold season and the last one annual growing degree days). The relationships between calculated GDDs and key variables that may affect temperature were carefully studied. (e.g. geographical data of latitude and longitude, elevation, nearest grid distance from the sea) Geographical distributions of GDDs were found to be correlated closely with the climatic types of different regions that are mainly based on relief. The distribution of the GDDs presented in the maps showed that the calculated values were close to the measured ones, which confirmed the validity of the GIS-based approach. In few cases significant differences between predicted and calculated values were observed, mostly in the regions with less number of weather stations. Consequently, the highly accurate generated maps can be used as a useful tool for prediction of crops and pests phonological events and crop modeling.

Development of wheat (Triticum spp.) is primary driven by temperature, but is also affected by other factors such as vernalization and photoperiod. Crop growth and development are often described in terms of calendar days. However, determining the development in terms of thermal time or physiological time is more accurate because it is an accumulation of the caloric energy needed for the occurrence of phenological stages. The objectives of this study were: (i) to determine the base temperature for key phenological stages of different winter wheat cultivars and (ii) to develop a phenological model using the base temperature for predicting the duration in terms of thermal time for different phenological stages. Eight wheat cultivars were selected according to their vernalization period to determine the base temperature for three critical developmental phases, i.e., planting to heading, heading to harvest and planting to harvest. For each cultivar, the base temperature for each critical period was estimated as well as the duration of the three key phenological stages in terms of thermal time for three locations in Georgia from 1999 to 2010. The base temperatures and the growing degrees varied widely depending both on the developmental stage and the cultivar. The estimated base temperatures for the eight wheat cultivars ranged from 3.1 to 8.1oC, 10.6 to 18.4oC and 1.6 to 8.4oC, for planting to heading, heading to harvest maturity and planting to harvest maturity. Also, the duration in Growing Degree Days (GDD) was determined for each season and cultivar. When 0oC was used as the base temperature, the GDD between cultivars varied from 1675-1844, 1017-1239 and 2827-2936oC from planting to heading, heading to harvest maturity and planting to harvest maturity, respectively. The results from this study provided specific base temperatures for each developmental stage for each individual cultivar and, therefore, provided a more accurate estimation of GDD. The variation in base temperature and GDD accumulation is probably a selective advantage for winter wheat. Clearly more work is required to estimate the base temperatures and duration for others phenological stages and further evaluation is required for additional cultivars and a wider range of environments.

Growing degree-days (GDD) is considered as an alternative indicator for counting calendar days in studying of crop phenology stages. In the current study, genetic diversity of 86 Iranian wheat cultivars and 184 landraces were investiagted based on the phenological stages (day to booting, day to flowering, day to maturity and GDD of these stages) along with grain filling period, thousand grain weight and grain yield during 2013-2014 growing seasons in augmented design with 3 control cultivars (Azar, Navid and Pishtaz) in 6 incomplete blocks in Agronomy and Plant Breeding research filed, University of Tehran. The results illustrated that there is a significant difference between cultivars and landraces, so that the cultivars had higher yield and less grain filling period than the landraces. On the other hand, the results indicated that the genotypes with different growth habits have a significant difference in terms of most of the phenological traits which it could be useful either in directly or indirectly selection for increasing the length of the grain filling period along with grain yield. Since the diversity of phenological traits were higher in landraces, they can be a valuable source for selection to improving these traits. Finally, due to the importance of the phenological stages and GDD index, it is recommended that these traits also consider as well as yield and yield components in order to obtain more accurate results.