Researches about selecting resistant melon types to fusarium oxyporum f. sp.melonis race 1,2 by using tissue culture and mutation techniques

Fusarium wilt is a vascular disease of the Cucurbitaceae family caused by the soil fungus Fusarium oxysporum f. sp. melonis (FOM), which is very detrimental to muskmelons (Cucumis melo L.). Fusarium wilt of melon is prevalent in temperate and tropical regions and causes a worldwide problem. FOM can survive in the soil for extended periods of time as chlamydospores, and is capable of colonizing crop residues and roots of most crops grown in rotation with melon. The only effective control is the use of resistant varieties. Four races of FOM have been identified, namely 0, 1, 2 and 1.2. Race 1.2 was further subdivided into race 1.2y and 1.2w, which cause yellowing and wilt symptoms, respectively. Two resistance genes (Fom-1 and Fom-2) have been identified in melons. Fom-1 confers resistance to FOM races 0 and 2, and Fom-2 confers resistance to races 0 and 1. These two genes are extensively used in breeding programmes, which can be assisted by marker assisted selection using markers linked to these resistance genes. No genes have been identified that confer resistance to race 1.2. However, polygenic recessive genes have been found to confer resistance to race 1.2 in Piboule genotypes. Melon production in Turkey is 1,700,000 tons and it is declining the year after year because of Fusarium wilt. Therefore, Fusarium wilt has a high economic importance in the cultivation of muskmelon in Turkey. In some parts of Turkey the prevalent races of this pathogen were determined. FOM has caused severe losses for farmers as our native cultivars are not resistant to this disease. It is believed our native cultivars will disappear if resistance to FOM is not introduced into the cultivated material. For this reason, many scientists in Turkey are focusing on research to develop new resistant cultivars via conventional and biotechnological breeding methods. In vitro techniques became widely spread during the 20th century, and their potential to make important contributions to plant breeding was quickly understood. In vitro techniques for crop improvement first consisted of micropropagation and plant regeneration, and then in vitro methods were also found to be useful for eliminating disease and selecting for resistant cells or explants. In vitro selection using specific chemical compounds and pathogens is another useful aspect of tissue culture. More recently, in vitro techniques were combined to mutation induction for generating genetic variation, including novel disease resistant mutants. Mutation induction can be caused by chemical or physical mutagens that alter the structure of the DNA. Treatment of in vitro tissues with physical or chemical mutagens may increase the frequency of genetic variation considerably. The physical mutagens most commonly used are X-rays, gamma rays and UV light, whereas Ethyl Methane- Sulphonate (EMS) is the chemical mutagen most used in crop improvement. Irradiation treatments may be a suitable choice of mutagen for a number of reasons because the application is fast and, in contrast to chemical mutagens, there is no risk that residues remain in the medium. In this research we are going to determine the resistant cells, which will come from irradiated and non-irradiated explants by using races of F. oxysporum f. sp. melonis culture filtrates in vitro conditions. If we will get successful results by this method we will be able to develop new melon cultivars, which will be resistant to F. oxysporum f. sp. melonis. The present work was performed with in vitro plantlets obtained from seeds of melon cv. Yuva which is an important commercial cultivar in Turkey. According to our observations filtrate and gamma ray treatment have an important effect on tolerant plantlet and callus formation. In this research, we show a method for mass-selection of melon mutants resistant to Fusarium wilt. In vitro selection of resistant cells, which are come from irradiated and non-irradiated explants, is done using culture filtrates of different FOM races. According to our results we determined effective irradiation doses and filtrate treatment dose by Linear Regression Analysis. According to our results 21.75 Gy is effective dose for in vitro Yuva cv. Explants to induce mutation and for filtrate treatment 6.73% is the proper dose to select survive calluses and plantlets. Hence we will carry out our near future experiments with these determined doses and so that this research can lead to the development of new melon cultivars that will be resistant to Fusarium wilt. (Includes 3 tables and 8 figures)