Due to the important role of cotton drought-tolerant varieties and the reported involvement in this trait of trehalose-6-phosphate-synthase, the respective gene (TPS) was isolated and characterized from cultivated cotton, Gossypium hirsutum (ZETA 2 cultivar), using a chromosome-walking technique. TPS has three exons comprising the coding region. Southern blot analysis indicated that the Gossypium genomes (A and D) contain a single copy of TPS per genome. In addition, the expression of this gene was studied in different plant tissues. Plants of the Australian cotton variety Siokra L23, known for its drought tolerance, were subjected to drought stress (using PEG 6,000 solution, for 4 h during the dark period of the day and for four consecutive days); leaves, stems and roots were collected after the end of the stress period. Total extracted RNA was examined for the presence of transcripts, in the above-mentioned tissues of stressed and well-watered plants, by reverse transcription-polymerase chain reaction (RT-PCR). The expression levels, determined semi-quantitatively, indicated that the gene was expressed in all plant tissues under both water availability conditions. However, increased expression levels of TPS were observed mainly in stressed leaves and roots compared to those of the well-watered control. This finding is in agreement with the fact that TPS participates in trehalose biosynthesis, known for its participation in stress signal transduction in higher plants.

Drought-tolerant cotton varieties are very important for Greece and throughout the world. Four Greek cotton varieties (Zeta 2, Zeta 5, Korina and Eva) and an Australian variety (Siokra L23) were subjected to three water-stress levels (0.0, –0.1 and –0.3 MPa). Morphological and physiological parameters studied were plant height, total leaf area, shoot, root and total plant fresh and dry weights, stomatal resistance (SR), water potential (Ψ w), and relative water content. Siokra L23 was confirmed to be the most drought-tolerant variety based on its high SR and Ψ w , it's having the smallest total leaf area, and expression of drought-tolerance-related genes. The Greek cotton varieties were ranked from most to least drought tolerant as follows: Eva, Korina, Zeta 2, Zeta 5.Molecular responses of the cotton varieties were studied by investigating the expression of five drought-tolerance-related genes, namely, trehalose-6-P synthase, heat-shock protein calmodulin-binding homolog, late embryogenesis abundant (Lea) proteins 14A and 5D, and NAD(P)H oxidase. Reverse transcription–polymerase chain reaction was performed utilizing total RNA samples isolated after a 4-d drought treatment (i.e. at the end of the stress period). Heat-shock protein calmodulin-binding homolog was induced by water stress in drought-tolerant varieties (Eva and Siokra L23) and Zeta 2. This correlation between physiological and molecular data for this gene allows it to be used in cotton breeding programs. Trehalose-6-P synthase and NAD(P)H oxidase genes were not expressed in almost all varieties and treatments. In contrast, the Lea genes showed, with minor exceptions, expression that was independent of variety and treatment. Eva and Korina varieties should be used under conditions of water shortage, whereas Zeta varieties provide a significant advantage to the grower when planted under conditions of high water availability.

Studies were conducted in four regions of central Greece (Larisa, Karditsa, Livadia, Thiva), to evaluate the productivity and fibre properties (fibre strength and fibre length) of the five most commonly grown cotton cultivars in these regions. The experiments lasted for 6 years (1995)(1996)(1997)(1998)(1999)(2000). All the characteristics tested were strongly influenced by the factors ÔyearÕ, ÔcultivarÕ and ÔregionÕ. Significant cultivar · region, year · cultivar, region · year and cultivar · region · year interactions occurred for all the characteristics studied. The cultivar Alegria had the highest seed-cotton and lint yield, while Aria had the lowest ones. Both cultivars gave the highest mean lint percentage but the lowest mean boll weight (MBW). Alegria had the lowest fibre strength, while Aria had the highest. The Acala-type cultivars, Acala SJ2 and Zeta 2, had intermediate seedcotton and lint yield, while Vered 171 had high seed-cotton and satisfactory lint yield. The three cultivars mentioned above had the highest MBW and very good fibre strength. Positive correlation was observed between fibre strength and length. In spite of the fact that mean fibre length was statistically the same in all cultivars, it was influenced by the factor ÔyearÕ, as a result of different weather conditions. The year 1996 was the most unfavourable one for seedcotton yield and MBW, because it was characterized by lower than average air temperatures and rather dry conditions for all study sites. The factor ÔregionÕ, a combination of different climatic conditions and cultural practices, influenced significantly all the parameters studied.