Different isolates of Fusarium oxysporum were isolated from tomato-wilted plants, grown under glasshouse condition at different location of Almaty - Kazakhstan. All isolates particularly isolate A caused typical symptoms particularly brown vascular discoloration in stem and negatively affected plant growth criteria and fruit yield/plant on the tomato cultivar Carolina Gold. The tested isolate A at least was identified as Fusarium oxysporum fsp. lycopersici (FOL) based on the characteristic Fusarium wilt symptoms. Sensitivity of seven tomato cultivars against FOL infection was evaluated. All investigated growth characters and fruit yield/plant were significantly lower in inoculated than un-inoculated plants of most tested tomato cultivars particularly Carolina Gold and Dona. The tested cultivars could be classified into three groups: 1) Susceptible cultivars (Carolina Gold and Dona), 2) highly resistant (EXP 1 and EXP 2) and 3) moderately resistant (EXP3, EXP5 and EXP4). In term of early fruit yield production, the moderately resistant EXP4 was significantly better than the highly resistant cultivars EXP1 or EXP2 then it could be subjected to further tests to introduce it as commercial cultivar in Kazakhstan. The aqueous extracts of garlic bulbs (Allium sativum L.) and seeds of black pepper (Piper nigrum) and salicylic acid and riboflavin were used at different concentrations as resistance inducer treatments. The in vitro growth and sporulation of FOL was completely inhibited by garlic (G) extract at conc. 3%, while, riboflavin (R) and salicylic acid (SA) did that at 3 and 10 mM conc., respectively. The black pepper (BP) extract was the least effective one in this respect where the fungus could grow and produced appreciable number of spores even at 4% conc. Spraying shoots (SS) of the 4 weeks old tomato transplants with BP extract at 4% conc., immersing their roots (IR) with G extract at 4% conc., or spraying shoots (SS) with G extract at 4% conc., completely suppressed the FOL infection and increased fruit yield production by more than 300, 200 and 160%, respectively whereas, the combined method (IR+SS) using riboflavin at 10mM reduced wilt disease severity by more than 88% and increased fruit yield production by more than 200% compared to the untreated control. The activities of polyphenoloxidase (PPO) and peroxidase (POD) enzymes were determined in leaves of treated and untreated (control) tomato plants after two months from inoculation. The increase in POD activity was higher and more pronounced than PPO. The increase in PPO activity, in most treatments, was ranged between 4.4% (IR/SS/BP at 4%) to 94.2% (SS/R at 0.1mM) although few treatments slightly decreased it. However, all tested treatments increased activity of POD enzyme by 60.7-1000.0% comparing to the untreated control treatment. After two months from FOL inoculation, the petioles of the fifth leaves of tomato cultivar Carolina Gold were treated by G or BP at 4% using the IR, SS or IR+SS methods were anatomically examined The microscopic examination showed induced positive changes in the water conductive elements particularly xylem vessels and width of the vascular bundles in treated compared with untreated (check) plants. These positive changes might involve in the induced systemic resistance which lead to resist or delay development of the Fusarium wilt disease in tomato plants. |
