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Swedish University of Agricultural Sciences (2006)

Improved seed handling techniques for Juniperus polycarpos

Daneshvar, Abolfazl

Titre : Improved seed handling techniques for Juniperus polycarpos implications for active restoration of degraded Juniper forests in Iran

Auteur : Daneshvar, Abolfazl

Université de soutenance : Swedish University of Agricultural Sciences

Grade : Doctoral Thesis 2015

Résumé
Juniperus polycarpos (K. Koch) is one of six native juniper forest tree species in Iran whose population size is declining continuously. The ultimate aim of the research presented in this thesis was to increase the regeneration potential of J. polycarpos by identifying factors influencing seed quality and develop methods that increase germination capacity and vigor. The research focused on impact of infection by dwarf mistletoe on reproductive output, methods for sorting unproductive seeds from seed lots, improving germination capacity and vigor through sorting techniques and by breaking seed dormancy. The results show that moderate level of infection significantly (p < 0.05) reduced mean number of cones per unit area of the host crown, increasing the number of damaged seeds, reducing seed size and germination capacity. For sorting viable seeds from non-viable seeds, three methods were applied : Incubation, Drying and Separation (IDS), modified specific gravity (SG) separation and near infrared spectroscopy (NIRS). For the IDS experiments, seven days incubation followed by nine hours of drying and sedimentation in pure water or 200 g sucrose /l water solution resulted in 75% and 82% sunken-viable seeds, respectively. For seeds soaked for 48 hours, SG separation in 600 g/l sucrose solution also resulted in 77% sunken-viable seeds. For both sorting techniques, only 4% of viable seeds were lost into the discarded floating fraction. NIR spectroscopy of individual seeds discriminated between viable and non-viable seeds of J. polycarpos with 98% and 100% accuracy, respectively based on spectral differences attributed to seed coat chemical composition and storage reserves. For finding optimal dormancy breaking treatment and subsequent stimulation of germination capacity and vigor of J. polycarpos seeds, different pretreatments were tested. The results showed warm stratification for sixteen weeks followed by twelve weeks of cold stratification resulted in 72% germination after 12 days compared with 16-week cold-stratification alone (42%) and the control (8%). Exogenous application of phytohormones alone or in combination with cold stratification resulted in less than 50% germination, though significantly (p < 0.01) higher than the control (8%). As a whole, the results have strong implication for active restoration by increasing seedling production potential in nurseries.

Mots Clés  : juniperus, forest trees, forests, seed, germination, seed dormancy, seed quality, grading, sorting equipment, parasitic plants, viscum album, infrared spectrophotometry, iran

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