Koksal Karadas

Effect of water stress and potassium iodide on yield and yield components in two wheat varieties

Drought is a major factor limiting crop growth and productivity. Under semi-arid and arid conditions unavailability of water limits grain yield (Chimenti et al., 2002). Studies aimed at an integrated approach to drought resistance should define the problems including the regularity of drought and its timing in relation to crop development (Clarke, 1985). The most sensitive stage is that of anthesis; characters most affected are grain yield, seed weight and number per spike (Wells & Dubetz, 1966; Ceylan, 1994). In the grain growing region, this period is in June. Cultivars with the ability to compensate against early senescence should be more tolerant to drought conditions (Turner & Nicolas, 1987). The identification of attributes useful for the process of screening genotypes for drought tolerance is a major challenge to the plant breeder. Because yield and drought resistance are controlled at separate genetic loci, improved drought tolerance involves the identification and transfer of physiological traits responsible for drought resistance to high-yielding and agronomically acceptable cultivars. Most physiological screening tests are too slow and complex to be suitable for testing large numbers of genotypes (Zhang et al., 1999). These disadvantages may be minimized when attributes of proven value can be identified in early developmental phases in controlled or partially controlled environments, and marker assisted selection techniques applied in the breeding process. Blum (1983) suggested that chemical desiccation could be used to screen for post-anthesis stress tolerance, as destruction of the plant’s photosynthetic system by desiccation would reveal those genotypes that were able to sustain translocation-based kernel growth. They found potassium iodide (0.6%) applied to leaves most accurately simulated the influence of drought (Nicolas & Turner, 1993). This technique applied in non-stress conditions gave grain yields and kernel weights that were correlated with yield under stress conditions (Turner et al., 1989). Morphological, physiological and anatomical characteristics of wheat have been identified, enabling plants to grow and survive in drought-prone conditions (Acevedo & Ceccarelli, 1989). High yielding genotypes show high crop ground cover during autumn and winter when water is available (Anon., 1994). Drought resistant genotypes show early flowering and a faster grain-filling period, thereby increasing yield (Blum, 1983), earlier heading, higher number of spikes per m, and higher grain weight per spike (Cooper et al., 1987); also dark green leaves before stem extension and light green leaves after stem extension (Richards, 1982), and accumulation of intermediary metabolites such as proline (Grummet et al., 1987) under drought stress. The objective of these studies was to determine the effect of different irrigation times on yield, some yield and quality components, and to evaluate the applicability of potassium iodide as a chemical desiccant in wheat.