Genotypic response and heritability of Fusarium oxysporum resistance in tomato

English: This study reviewed principal aspects relating to Fusarium wilt race 2 resistance in tomatoes, caused by the fungus Fusarium oxysporum f. sp. Iycopersici. The classification and life cycle of Fusarium wilt, the symptomatology, disease assessment and host-pathogen interaction was reviewed. Different methods of disease management were investigated, with emphasis on genetic control. Twelve inbred tomato cultivars grown in South Africa were screened for resistance to Fusarium oxysporum f. sp. Iycopersici race 2. Percentage resistant plants, and disease progress were monitored over intervals of 30 and 60 days respectively. Significant differences were found between cultivars for percentage resistant plants for both intervals as well as for disease progress. Five cultivars, Floradade, Rodade, Heinz 1370, Traffic Jam and Sixpack were associated with resistance after 60 days screening, while Rossol, Oxheart, Red Kaki and Roma were found to be highly susceptible after 60 days. The cultivar x day interaction was significant for the percentage resistant plants. Fusarium wilt resistance was then studied in six of the inbred tomato cultivars viz., Rossol, Red Kaki, Moneymaker, Rodade, Flora Dade and Heinz 1370 and their F1-hybrids. Percentage resistant seedlings for each cultivar and their F1- hybrids were determined after 30 and 60 days assessment. Disease progress was also calculated. Variance analysis indicated significant genotype x day interaction for Fusarium wilt. Significant differences were found between entries after 30 and 60-days assessments as well as for disease progress. The best Fusarium wilt resistance was found in the cultivars Moneymaker, Rodade and Flora Dade. Moneymaker also had the best disease progress. Disease progress in five of the crosses Flo x Man, Flo x Ros, Rad x Ros and Man x Ros were less than 10%. Disease progress in the F1-hybrids were significantly lower than in the inbred lines, which emphasis the efficiency of tomato hybrids to reduce the levels of Fusarium wilt in tomato. Another objective of this study was to determine the combining ability and heritability of Fusarium wilt resistance in tomato. Six inbred tomato cultivars Rossol, Red Kaki, Moneymaker, Rodade, Flora Dade and Heinz 1370 were crossed in a diallelic manner to produce 15 F1-hybrids. Assessment for Fusarium wilt resistance was done after 30 and 60 days and for disease progress. Significant differences were found for GCA- and SCA- effects. The GCA: SCA ratio's for 30 and 60 days assessments indicating both additive and non-additive gene actions. Disease progress was mainly controlled by dominant effects. The narrow sense heritabilities for Fusarium wilt resistance were respectively 12% and 8% after 30 and 60 days assessments. Significant levels of heterosis were observed in crosses for Fusarium wilt resistance. The cultivar Heinz 1370 had the largest GCA-effect while the cross Rod x Ross possessed the largest SCA-effect. PCR technology with specific DNA primers and tomato leave cDNA was used to investigate the presence of different single genes in six local tomato cultivars. These cultivars included Flora Dade, Rodade, Moneymaker, Heinz 1370, Rossol and Red Kaki. The presence of the single genes 12C1, 12C2, 12, 12C3 and 12C5 were tested for as they were suspected of being responsible for Fusarium wilt race 2 resistance. The 12C1and 12C2genes were identified in all cultivars except for Rossol that did not possess the 12C1 gene. No 12C3 or 12C5 genes were identified in any cultivars. The 12 gene was only identified in Flora Dade and Rodade. In three of the cultivars significant relationships could be found between the 12 resistance alleles and their breeding values.