Identification And Inheritance Of Resistance Analysis To Fusarium Oxysporum F.sp. Niveurm In Watermelon

Watermelon (Citrulls lanatus ) is one of the most important fruit crops in the world and accounts for 20% of the world's total vegetable production area (FAO, 2007). Fusarium wilt of watermelon, caused by soil-borne fungus Fusarium oxysporum f. sp. niveum (Fon), is one of the most severe vascular diseases worldwide. In this study, The identification of resistance to fusarium wilt of watermelon and the analysis for inheritance to different races were studied. The main results were as follows:1. Depending on differential hosts such as BlackDiamond, SugarBaby, PI296341-FR and CalhounGray, a perfect identification technology for watermelon Fusarium wilt was established. Based on this systerm, 17 watermelon germplasms were inoculated Race0, 1, 2 respectively. the result showed that RZ-900, JLM, BlackDiamond, PI595203, PI482271 were identified as susceptible materials to Race0; 8 watermelon germplasms showed resistance to Race1, including accessions: 97103, Sugarlee, JX-2, JLM, PI5386019, PI296341-FR, PI482271, PI482303. Specially, PI482303 and PI296341-FR were identified as resistant materials to Race 0, 1 and 2 simultaneously. The identification results provided a reference for Fusarium wilt resistance breeding in watermelon.2. A RILs(F₂S₈) populations derived from PI296341-FR (resistant to Race1) and 97103 (susceptible to Race1) were used to investigate the inheritance of resistance to Race1 of Fusarium oxysporum f.sp.niveurm. Using the mixed inheritance model of major gene plus polygene, the resistance to Race1 of Fusarium oxysporum was showed to fit one pair of additive major genes model (B-3 model ). The equal additive effect value was 0.8, with a recombination rate of 0.27. The inheritance of major genes were estimated to be 98.5%.3. A RILs(F₂S₈) populations and six generations populations (P1, P2, F1, B1, B2, F2) derived from PI296341-FR (resistant to Race2) and 97103 (susceptible to Race2) were used to investigate the inheritance of resistance to Race 2 of Fusarium oxysporum f.sp. niveurm. Using the mixed inheritance model of major gene plus polygene, the resistance to Race2 of Fusarium oxysporum was showed to fit one pair of additive-major genes plus additive-dominant polygene model (D-2 model). In B1, B2 and F2 populations, the heritability of major genes with recessive effect was estimated to be 31.8%, 23.4% and 48.6% respectively, and the polygene heritability ranged from 16.5% to 43.9%. Meanwhile, three linkage major genes with equal additive effect (F-3) were found to govern the inheritance of resistance to Race 2 of Fusarium oxysporum in the RILs(F₂S₈) population, and the inheritance of major genes was estimated to be 66.2%, additive effect was -0.51. The recombinant rate between three major genes was about 0.16. This result indicated that the resistance to Race2 of Fusarium oxysporum in PI296341-FR was controlled by both major and minor genes, and the additive and dominant effects of minor genes were higher than major genes.4. In the RILs(F₂S₈) population, the correlation analysis to resistance heritability between Fusarium wilt Race 1, 2 were studied. The result concluded that the correlation coefficient between Race1 and Race2 was 0.283. And the heritability of Race1 was 86.32% and Race2 was 55.42%. Meanwhile, by comparing the resistance identification from the same RILs(F₂S₈) population, only found 35% of strains showed the same resistance identification result between Race1 and Race2. In total, the inheritance of resistance to Fusarium wilt Race1 and Race2 were controlled by two independent genetic factors respectively, while linkage relationship may existed between the genetic factors.