Selection of phosphorus deficiency-resistant tomato genotypes and characterization of phosphorus efficiency mechanisms by morphological and physiological aspects

Low levels of available P in soils limit the plant production. Although total P concentrations are generally high in soils, because of some soil characteristics (low and high pH, high CaCO3, low organic matter etc.) in soils, it might be fixed in unavailable forms. Under P-limiting conditions, plants have developed some adaptation mechanisms such as changes in root morphology, increased root exudates, enhanced releases of acid phosphatase and phytase, increased root uptake of P, to survive. Because of these reasons, it can be thought that selection and cultivation of P efficient species and cultivars of a species might be very helpful for both economical and environmental aspects. In this PhD study, there was very large variation among P efficiency values of tomato genotypes. The most distinct differences between P-efficient and P-inefficient cultivars were shoot and root growth and P content under P-limiting conditions. At low P supply, P concentration in shoot was similar in all cultivars. However, it has been observed that, in sensitive cultivars, antosian accumulation in the leaves which appears in reddish-purple colour, was much higher. In the experiment dealing with the possible role of P uptake in P efficiency of tomato cultivars, it has been found that among the plants pre-cultured with low P, there was a good relation between P uptake and P efficiency of the genotypes used in this experiment. It is just to say that the Pefficient cultivars took almost 30% more P up and had higher P absorption rates than the P-inefficient cultivars. In the experiments conducted to see the role of possible physiological traits of plants such as acid phosphatase and phytase activities of roots, although the activities of both enzymes were increased under P limiting conditions, no relation was found between them and P efficiency of genotypes. Key words: Phosphorus Deficiency, Tomato, Efficient Genotypes, Phytase