| Soil acidification is becoming increasingly serious in facilities due to irrational planting,excessive fertiliser application in the blind pursuit of yield,and monoculture planting.Soil acidification can cause soil-borne diseases,and tomato wilt is a worldwide disease caused by Fusarium oxysporum f.sp.Lycopersici(FOL),which can severely reduce yields and even lead to crop failure.In order to investigate the effect of pH on the development of tomato wilt,this experiment was designed to treat tomatoes in acidified pots with six pH gradients(4.5,5.0,5.5,6.0,6.5,7.0).The results of the experiment were as follows.(1)Effect of pH on the growth and reproduction of FOL.pH4.5 was the most unsuitable for the growth and reproduction of FOL,the production of fusarium acid and the expression of pathogenic genes.The pH5.5 treatment was the most suitable for the growth and germination of FOL,with the highest concentration of fusarium acid production and cell wall degrading enzyme activity.pH5.5 is Conditions favoured the expression of virulence genes FUB4,FUB5,FUB8,Sge1,FVS1 and TOM1,reaching significant levels compared to the other treatments.pH6.5 treatment had lower expression of pathogenicity genes and FOL was the least pathogenic.This indicated that Fusarium acnes growth and pathogenicity were enhanced in acidic soil at pH 5.5,making it easier for tomato roots to be infected.(2)Effect of soil pH on tomato growth and disease resistance.As soil pH(4.5-6.0)decreased the malondialdehyde content gradually increased,the rate of superoxide anion production increased and the reactive oxygen content in the root system increased.Soil pH(6.5-7.0)showed the best growth of tomatoes,with lower levels of reactive oxygen species and free radicals in the plant,which tended to be in equilibrium.A variety of defensive enzymes(POD,SOD,PPO,PAL)increased in activity in response to the production of reactive oxygen species,reducing damage to the plant.(3)Effect of soil pH on the occurrence of tomato wilt.The disease index showed a trend of increasing and then decreasing with increasing pH.Tomato wilt occurred most severely at soil pH5.5,with the highest abundance of Fusarium acnes in plant vascular bundles and soil,when mycelial dry weight,colony diameter and spore germination rates were best and the highest toxin concentrations were produced,and were significantly higher than in the other treatments.The rate of superoxide anion production in the roots was accelerated and malondialdehyde accumulation increased,inducing an increase in the activity of various defence enzymes such as POD,SOD,PPO and PAL.The disease index was lowest at soil pH(6.5-7.0)and defence enzyme activity levelled off.The expression of Sl NPR1,Sl PR1,Sl I-2and Sl FRG3,which are important genes in tomato disease resistance,reached the peak at pH6.5,which was significantly higher than the pH5.5 treatment.The correlation analysis showed that the expression of disease resistance genes was negatively correlated with the disease index(P<0.01),indicating that tomato had the strongest defence capacity at pH6.5,when soil pH was not conducive to FOL growth and reproduction.In summary,the fastest growth and reproduction of FOL,the highest concentration of toxin production and cell wall degrading enzyme activity were observed at pH5.5,indicating that this was the time of highest pathogenicity and easier infestation of the tomato root system resulting in the highest disease index.The disease index was highly significantly positively correlated(P<0.01)with the number of pathogens in the soil,cell wall degrading enzymes produced by FOL and the growth rate of mycelium and spore germination,and negatively correlated(P<0.01)with disease-resistance related genes.Increasing soil pH(6.5-7.0)reduced the pathogenicity of FOL and reduced Fusarium wilt caused by Fusarium acuminatum in tomato. |
