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Abstract Tomato Lycopersicum esculentum Mill is considered one of the most important vegetable crops grown for human consumption. This crop has an increasing importance now days especially in those countries with rapidly expanding population, e.g., Africa and Asia, where tomato production has duplicated three times since 1990 (CABI ,2011). Tomato known as one of the crops to be infected particularly with Fusarium pathogen. Fusarium oxysporum f. sp. lycopersici, represented a real threat to tomato production all over the world. This study included : investigation the virulence of 15 isolates of Fusarium oxysporum f. sp. Lycopersici collected from 5 governorates of Delta Egypt, evaluation of 5 tomato cultivars to this fungus, characterization of these isolates for presence and absence of genes SIX1, SIX2, SIX3, SIX4, SIX5, SIX6, SIX7 and SIX8 using molecular technique based on PCR polymorphism analysis , capability of the tested Fusarium isolates to produce Fusaric acid under in vitro conditions through using High Pressure Liquid chromatography (HPLC) analysis , relation between Fusaric acid accumulation and the aggressiveness of Fusarium isolates toward tomato plants and evaluation of three Trichoderma spp. and two bacterial bio-agents in controlling the pathogen in vitro and the disease in vivo. The obtained results illustrate the following data: 1- All the fifteen isolates were pathogenic toward tomato plants and caused symptoms corresponding to the Fusarium wilt disease. Moreover, results revealed that the tested isolates varied regarding to their aggressiveness and virulence potential under the bioassay conditions. 2- The highest percentage of disease severity i.e. 61%; 52%; 44%; and 41.65% were recorded within isolates 4 , 5,15, 2, respectively. On the other hand, isolates 8, 12 and 14 resulted in the lowest disease severity percentage on tomato plants (8.79%; 9.70% and 9.79%, respectively). 3- Evaluation of five tomato cultivars revealed that the cultivar Super Strain B showed moderate response to the wilt pathogen of tomato, While Yara and Super Marmande cvs. were highly susceptible. The other tomato cvs. were in between in this regard. 4- The results showed that amplicons of SIX1 were detected with all tested isolates except isolates 8, 12, 14 and 15 in addition to the nonpathogenic isolate, Fo162. Also,amplicons of SIX5 were detected only within isolates 2, 3, 4, 5, 7 and 15. Additionally, amplicons of Six6 were detected within all pathogenic tested isolates except isolates 1, 6, 7, 8, 11 and 12. In contrary, no amplicons for SIX2, SIX3, Six4, SIX7 and Six8 were detected among all Fusarium oxysporum isolates subjected to the test.. 5- The present study suggests that the presence of SIX1, SIX5 and SIX6 genes within Egyptian isolates of Fusarium oxysporum f.sp. lycopersici can be used, for some extent, as a remarkable indicator for virulence potential on tomato plants under certain conditions. 6- Regarding with fusaric acid accumulation, results of 4 weeks after inoculation demonstrated that the highest amounts of FA were 13000, 11101, 6559 and 3936 mAU*S of isolates 4, 8, 6 and 10 respectively. While the higher amounts of FA at 6 weeks post inoculation were 22926, 12136, 10991 and 10451 mAU*S, of isolates 3, 2, 4 and 12, respectively. On the other hand, the highest amounts of FA at 8 weeks post inoculation were 60816, 42926 and 37275 mAU*S of isolates 8, 12 and 4, respectively. 7- HPLC chromatogram analysis illustrates that, A- At 4 weeks post inoculation, in -spite of the highest disease severity was recorded with isolates 12, 3, 4 while only isolate 4 showed relative high ability to produce high concentration of FA comparing to the other isolates . B- At six weeks after inoculation, the results showed that the most virulent isolates were 12, 2, 3, and 4 produced the highest concentrations of FA comparing to the other isolates. C- At eight weeks post inoculation, the results showed that among the most virulent isolates (12, 2, 3 and 8) only two isolates, 12 and 8 recorded relative high FA accumulation, while the other two isolates 2, and 3 exhibited relative low FA producing capability comparing to other isolates . 8- Regarding to the accumulation of total secondary metabolites within the tested Fusarium isolates, the chromatogram analysis indicated that, A- The highest concentrations of total secondary metabolites were observed with isolates 8, 4, 7 and 1, respectively at four weeks post inoculation. B-At six weeks post inoculation, the highest concentrations of total secondary metabolites were 48654, 34517 and 26511 mAU*S which recorded with isolates 10, 11 and 12, respectively (Figure 12). C- At 8 weeks post inoculation, showed that isolates 4, 12, 11 and 1 produced the highest total secondary metabolites expressed as 91904, 89328, 49585, 42268 mAU*S, respectively (Figure 12). 9- The present study illustrate that the all tested Egyptian Fusarium oxysporum isolates are able to produce FA mycotoxin under the test conditions. It seems and for some extent, FA plays a distinctive role in the Fusarium wilt disease development on tomato plants during the middle and last stages of infection while this role is almost missing at the primary infection stage. 10- Further studies focus on fractionation, purification and identification of some novel distinguish secondary metabolites which are accumulated within FA are highly needed to figure out whether FA alone or combined with other substances can be involved in the interactions between Fusarium oxysporum pathogenic isolates and their host plants. 11- Regarding biological control study, the obtained results showed that all the tested bio-agents showed low to moderate effect in suppressing radial growth of the pathogenic fungus. 12-The bacterial bio-agents isolate of B. subtilis and P. fluorescens was more effective than Trichoderma spp either in vitro or in vivo. 13-Both the healthy and oxidore fungicide enhanced the growth parameters (length of plants; length of root and fresh weight and dry weight) rather than the fungal / bacterial antagonists investigated compared to the control. |