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University of Kassel (2009)

Ecophysiology of seed dormancy and salt tolerance of Grewia tenax (Forssk.) Fiori and Ziziphus spina-christi (L.) Willd.

Sohail, Muhammad

Titre : Ecophysiology of seed dormancy and salt tolerance of Grewia tenax (Forssk.) Fiori and Ziziphus spina-christi (L.) Willd.

Auteur : Sohail, Muhammad

Université de soutenance : University of Kassel

Grade : Doktor der Agrarwissenschaften (Dr. agr.) 2009

Sommaire partiel
The overall forest cover of Pakistan is only 4.8% of the total land area. At the same time, Pakistan’s deforestation rates are alarmingly high and threatening the lives of many people who are dependent upon them for their livelihood. More than 70% of the country area is exposed to arid and semi-arid tropical climate conditions including 11.5 million hectares of deserts which are characterized by extreme temperatures and erratic rainfall. These dry areas are suffering from recurrent droughts and their vegetation cover greatly depends on the amount of precipitation. Increasing aridity and soil salinity are considered important abiotic factors that threaten crop biodiversity and ultimately land degradation in these areas. Drought and salinity stress are interrelated ecophysiological phenomena and cause many problems for seed germination and plant growth inducing physiological and biochemical disorders in metabolic processes. Utilization of salt tolerant plant species is considered a sustainable adaptation strategy to soil salinity in drylands, which is otherwise impossible to manage through agronomic or engineering practices. Trees and shrubs, which are adapted to local conditions, can play a vital role to combat dryland salinity and rehabilitate degraded lands. The potential role of indigenous multipurpose fruit trees has often been overlooked in this contest. Some of these species are very important to rural population to secure their livelihood. Pakistan harbors many tropical fruit tree species. Grewia tenax (Forssk.) Fiori and Ziziphus spina-christi (L.) Willd. are two indigenous tropical fruit trees that grow wild and are extensively used by the rural population. Their fruits are edible and consumed either fresh or dried and their leaves provide palatable fodder for livestock especially during the dry periods of the year. Despite their great ability to withstand drought and high temperature, wild stands of the species are sparse. Seed dormancy is a typical feature of dryland tropical species facilitating their survival under unfavorable climatic conditions. At the same time, increasing dryland soil salinity might be a possible threat to seedling survival. As emergence and early seedling growth are critical stages in the survival of most woody plants, seed germination and sensitivity of seedlings to soil salinity are important areas of research. This thesis comprises three experiments conducted under controlled climatic conditions to study how to overcome seed dormancy and to examine seedling’s ability to tolerate NaCl salinity. The results of the study about seed dormancy breaking of G. tenax show that incubation of seeds at 40°C for 4 weeks before sowing significantly increased total germination from 20% (control) to 70%. Heat incubation also significantly reduced days to first emergence and mean days to emergence as compared to the untreated control. The results indicate that seeds of G. tenax have a physiological dormancy which can be overcome by pre-sowing heat treatment of seeds (constant heat exposure) at 40°C for 4 weeks.

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