In vitro microbial contaminations are the most serious problems in plant tissue culture. Initial attempts for micropropagation of Dionysia tapetodes, a beautiful alpine cushion plant from north-east Iran, led to 100% explants contamination. Hence, the present study was conducted to develop an efficient surface sterilization protocol for in vitro culture of field collected D. tapetodes using combinations of different disinfection agents including sodium hypochlorite (NaOCl), ethanol and mercuric chloride (HgCl2) in different concentrations and exposure times. The most effective sterilization treatment with 91.6% healthy explants was the application of 0.1% mercuric chloride for 4 min. However, mercuric chloride in higher concentration (0.2%) was toxic to explants tissues and resulted in 41.66% necrosis. Moreover, the results indicated that in spite of being a general disinfectant in tissue culture studies, NaOCl was not as effective as mercuric chloride in elimination of microbial contaminations and led to 75% total infection when used in concentration of 3% for 15 min. The current experiment represented a potential method for disinfection of D. tapetodes and provided aseptic and clean explants for future in vitro culture studies. Manuscript profile

In the floriculture industry, the need for heat tolerant bedding plant cultivars is increasing because of the rising temperature around the world. A pot experiment was carried out to examine the impacts of four heat stress durations (0, 7, 14 and 21 days) on growth and ornamental traits to determine the relative heat tolerance of four cultivars of calendula (Calendula officinalis). Growth and development were quantified by measuring plant height, total leaf area, shoot and root fresh weight, shoot and root dry weight, time to flowering, flower number, average flower size, and flower longevity. Plant height, leaf area, and shoot and root growth at 35-42°C were significantly lower than those at normal temperatures (20-30°C). Time to flowering increased with temperature. Flower number, size and longevity were reduced by heat stress, so that among all durations, plants exposed to heat stress for 21d had the least mean. Longer heat stress reduced the plant height, leaf area, shoot and root growth, SPAD value, flower diameter and flower longevity of all cultivars., However, the range percentage reduction in growth and flowering parameters were different among cultivars. Experiment to determine the membranedamageshowed an increasein percent electrolyte leakage with exposure of plants to higher temperatures. The studied cultivars differed in their sensitivity to heat stress. The results indicated that better cell membrane stability, higher shoot and root growth, and later flowering led to greater heat tolerance in ‘Indian Prince’ compared to other cultivars. Manuscript profile

Studying the phenology of valuable native plants which are on the verge of extinction, is very important and effective for better introduction and protection of them. Fritillaria raddeana is one of the native bulbous plants with ornamental and medicinal value in Iran. The aim of this study is to investigate the phenological stages of F. raddeana as a first step to protect it and later to introduce it. In a natural habitat, in northern Khorasan province, Iran, six zones were selected at a distance of 1000 m from each other, and five plants were selected and coded in each zone. To provide a standardized phenological description of the species, this study used the BBCH scale. In total, from sprouting to winter rest, six main principal stages were described for sprouting, leaf development, inflorescence emergence, flowering, fruit development, fruit maturity, senescence, and beginning of dormancy stages and within them, 15 secondary growth stages were described. Data were collected once a week in the course of the vegetative season and with a 30-day interval during the dormant season for two consecutive years (2015-2017). Additionally, we measured some traits of plant growth. During the first year, sprouting and subsequent leaf development began in late March and the inflorescence emerged in the middle of April. The full bloom occurred in the first half of May and then seed formation (in the late of May). The summer dormancy was triggered in late spring. During the second year of study (2016-2017), the results showed the growing stages start with a delay of 5-8 days compared with the previous year. In addition, the means of studied growth plant traits such as leaf number, plant height, flower stem length, flower number, and flower diameter were significantly higher in the first year than in the second one. Manuscript profile