Effect Of Potassium On Tomato Physiology Indexes For Stress Resistance And Controlling Root Knot Nematode

The experiments with hydroponics and soil culture were conducted to determine the effects of potassium on physiology indexes in different tomato cultivars with inoculation of Meloidogyne incognita. The tomato yield, phenolic compunds and activities of defensive enzymes were investigated to explore the mechanism of disease resistance of K. The results in this experiment were showed as follows:1) The tomato yield in the soil culture conditions in potassium(K)application treatments were significantly higher than that of no K application. The maximum fruit weight was occurred in K4 (K₂O 1200kg/ha) treatment; K1 treatment was highest in average fruit weight at soil without root knot nematode while K3 treatment was highest in average fruit weight at soil with root knot nematode; K₂ treatment (K₂O 600kg/ha) was highest in both fruit number per plant and yield per plant. K₂ treatment was the best fertilization than others on improving the yield of tomato.2) The root infection rates in both of cultivars were significantly suppressed by K application, compare to the treatment without K. In hydroponics experiment, the disease index of root knot nematode of the resistance variety was significantly lower than that of susceptible one, but the effect of reducing disease incidence was better in susceptible tomato than in resistance one at the same K level. Increasing K levels(0-8mmol/L) enhanced the ability of resistance to root-knot nematode on both cultivars, but excessive K concentration(16mmol/L) in nutrient solution showed adverse effects. The highest reduction of infection rates in both varieties were noted in plants which fed with 8mmol/L K in hydroponics experiment and grown up with K₂ treatment in soil culture experiment.3) The activities of superoxide dismutase(SOD), peroxidase(POD), catalase(CAT), Phenylalanine ammonia lyase(PAL), and polyphenoloxidase (PPO) in the treatments with K were significantly higher than that of treatment without K. All kinds of enzyme exhibited similar pattern of activity dynamic change. They were markedly higher(P=0.05) in inoculated treatment than untreated controls. The largest rise in enzyme activities were observed in 10th day following treatment and they were decreased straightly until the experiment was done. The resistant variety was notably higher in activities of defensive enzyme than susceptible one through duration of trial. The highest activity, the fastest emergenc and the latest maintains duration of all enzymes,were occurred in 8mmol/L and K₂ potassium treatment. In addition, the cultivars-by-potassium interaction was highly significant(P=0.05), indicating that the response of SOD, POD, CAT, PAL, and PPO activity to K supply were significantly diverse in different cultivars.4) The content of malondialdehyde(MDA) in all treatments of K was significantly lower than that of treatment without K. The largest rise of MDA content appeared in 10th day in treatment of inoculation and then decreased sharply, while the treatment of non-inoculation was nearly constant during the whole duration of trail. The variety of HR was significant lower in the content of MDA than HS. Plants grown with 8mmol/L potassium had the lowest content of MDA.5)The dynamic changes in content of total phenolic, flavonoid and SA presented similar pattern with enzyme activities. The content of total phenolic, flavonoid and SA were significantly higher, compared with non-inoculation controls, on the variety of HR than HS. Plants grown with 8mmol/L potassium and K₂ fertilization (K₂O 600kg/ha) had the greatest content of total phenolic, flavonoid and SA.In summary, reasonable potassium can significantly increase the capacity of tomato against root knot nematode, while increasing the yield and endogenous defense enzymes and content of resistant material, to play a potassium play in the tomato disease resistance role in providing a scientific basis.