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Harbaoui K.,National Agronomic Institute of Tunisia | van der Lee T.,Plant Research International B.V | Vleeshouwers V.G.A.A.,Wageningen UR Plant Breeding | Khammassy N.,Tunisian National Institute of Agricultural Research | And 2 more authors.
Potato Research

Severe late blight epidemics in Tunisia in recent years prompted population studies on the pathogen responsible for this disease, Phythophthora infestans. Characterisation of 165 Tunisian P. infestans isolates collected from 2006 to 2008 was performed for the mating type and mt haplotype, while subsets were analysed for metalaxyl sensitivity (n = 65), virulence on differential set of 11 R genes of Solanum demissum (n = 31), aggressiveness on cv. Bintje (n = 36) and measurement of the radial growth on agar medium at three temperatures (n = 38). Most isolates from potato and all isolates from tomato had the A1 mating type. The A2 mating type was detected in the north-east and northern areas, but not in the north-west. All the A2 mating type isolates were metalaxyl resistant and seem to be part of a new generation of the P. infestans isolates which are more aggressive, with more complex races, and tolerant to higher temperatures. The increased severity of epidemics during 2006 to 2008 can be attributed to favourable weather conditions during growing seasons, adaptation of new genotypes, widespread phenylamide resistance in potato production regions and most probably incorrect spray programmes. In contrast to the presence of complex pathotypes in two major potato crop regions (north-east and northern areas), the P. infestans population detected in the other regions and in tomato crops was still relatively simple. Compared with the situation in Europe and the American continent, or even compared with neighbouring countries such as Algeria, the genetic changes in Tunisia are still comforting and require strict management decision on late blight control to avoid the spread of new P. infestans populations from Europe or neighbouring countries. © 2013 EAPR. Source

Jedidi E.,Tunisian National Institute of Agricultural Research | Mahmoud K.B.,Tunisian National Institute of Agricultural Research | Kaaniche-Elloumi N.,Tunisian National Institute of Agricultural Research | Jemmali A.,Tunisian National Institute of Agricultural Research
Acta Horticulturae

Somatic embryogenesis can be induced in vitro in many plant species and is interesting for its potential applications in clonal propagation, genetic improvement and embryo development studies. In cactus pear, embryogenesis has been previously tried on vegetative explants such as shoot apices and in vitro plantlets discs. In this work, embroyogenic process was induced from generative explants consisting in ovule, extracted from flowers, 10 days after anthesis. These explants were cultivated in MS medium containing 87 mM fructose and 3 μM GA3. Cultures were held in darkness in growth chamber at 25 ± 2°C. Light Microscopy, Scanning Electron Microscopy (SEM) and histology were used in this study to describe the main morpho-anatomical events during the whole embryogenic process. Indirect somatic embryogenesis was induced on ovule explants through callus formation near the micropylar region. SEM observation of a regenerated callus revealed that it is covered by proeminent structures which were small and tightly packed. These structures progressed asynchronously giving rise to somatic embryos at different developmental stages ranging from globular to cotyledonary. Moreover, different embryo phenotypes including normal embryos with two distinct cotyledons and abnormal monocotylated or polycotylated ones have been observed. Secondary somatic embryos were also observed during induction of embryogenic process resulting in interruption of primary embryo development. Histological observations showed that callus cells involved in somatic embryo formation contained a large nucleus with conspicuous nucleolus and dense cytoplasm. Longitudinal section of a well developed embryo showed that it constituted with two cotyledons, shoot apex and leaf primordia. Concerning secondary embryos, their regeneration took place at the expense of the primary embryo protoderm. Conversion of the normal embryos to plantlets was easily realized in 0.3 μM GA3 containing medium. © 2015, International Society for Horticultural Science. All rights reserved. Source

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