| Fungitoxic effects of 12 plant extracts were studied against fruit rot-causing fungi, viz. Alternaria alternata, Monilinia fructicola and Penicillium expansion in vitro. The results showed that three kinds of plant extracts had remarkable inhibitory effects not only in vitro experiment but also in vivo test in peach and apple fruits. The enzyme activities of phenylalanine ammonia-lyase (PAL), polyphenoloxidase (PPO) and peroxidase (POD) induced by plant extract No. 2 was also discussed. The main conclusions are as follows:Firstly, two test methods in vitro showed fungitoxic activities of 12 plant extracts in different degree to the three rot-causing fungi. Plant extracts No.2,5, 12 were more inhibitory against A.AlteRnata than the other ones, and their minimal inhibitory concentrations (MIC) on A.alternata were 6.25,1.65, 2.50 mg/ml, meanwhile their minimal Fungicidal concentrations (MFC) were 25.00, 6.25 and 5.00 mg/ml, respectively; Extracts of No. 2. 3, 5. 12 appeared to have obviously antiseptic activities against M. fructicola. Their MIC on M. fructicola were 6.25. 1.65,1.65 and 1.25 mg/ml, and MFC were 2 times of their MIC; Plant extract No.2 and No.5 appeared antifungal to P. expansum, and its MIC and MFC were 25.00 mg/ml and 50.00 mg/ml respectively, while these of No.5 were not detected. It was found that No.5 only inhibited spores germination rate of P. expansum, but it could not kill them.Secondly, the controlling effects of plant extracts screened previously on fruit rots were determined in harvested 'Rui Guang No. 18' peach and 'Golden Delicious' apple fruits during storage. Fruits were wounded and artificially inoculated with spores (5 ×104 spores /ml) of A. alternata, M. fructicola or P. expansum following the application of plant extracts . All the fruits were stored at 25℃ after treatments. The results indicated that M. fructicola rot of peach fruits could be controlled by plant extracts No. 2,3, 5 obviously besides No. 12.Treatments of plant extracts No.2, 5 or 12 all significantly reduced disease incidence and severity of A.alternata rot in apple fruits compared with the control, the higher the concentration, the better the effects showed.M. fructicola rot of apple fruits could be remarkably suppressed by plant extracts No.2 , 3, 5, 12.All treatments with 50 mg/ml of extract No.2 , 12.50 mg/ml of No.5 and 10.00 mg/ml of No.12 resultedin better disease control and showed the similar inhibitory effects as the treatment with iprodione (CK-)(P < 0.01). Plant extract No.3 was a perfectly natural preservative and made zero disease incidence forfruits treated with its MFC.In addition, the apple fruits treated with three concentrations of plant extract No.2 had lower infection rates and smaller lesion diameters than CK for P. expansum disease. The concentration of 200.00 mg/ml was the most suppressant to P. expansum .Thirdly, activities of PAL, PPO and POD induced by inoculation with plant extract No.2 (25.00 mg/ml) alone or No.2 + M. fructicola were studied in postharvest apple fruits. The activities of PAL and PPO in fruits after inoculation with No.2 maintained at a high level throughout the experiment. PAL and PPO could also be increased by infection with artificial wound and M. fructicola, but the levels ofactivity were lower than those above-mentioned. This result was in accordance with in vivo experiment in which there was no rot fruit after treatment with 25.00 mg/ml of No.2, but CK showed a disease incidence of 100% and higher lesion diameter. However, fruit inoculated with No.2 alone or No.2 + M fructicola did not stimulated POD activity. In a word, the results suggested that activation of these defense enzymes might also involve in the action of plant extract against M. fructicola, in addition to its fungitoxicity.
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