Screening And Identification Of Saline-alkali Tolerant Trichoderma Strains And The Study On Disease Resistance, Growth Promotion And Salt-tolerant Mechanism

In this study, saline-alkali tolerant Trichoderma strains were separated from saline soil samplescollected from Tianjin, Shandong and Hebei province. Then carried out functional studies such asdisease-resistance, plant growth-promoting and their potential in promoting plant growth by alleviatingnegative effect of salinity. Their mechanisms of saline-resistance were also discussed. The specificresults are presented as follows:1.20saline-alkali tolerant Trichoderma strains were selected from48saline soil samples collectedfrom Tianjin, Shandong and Hebei province through the flat panel dilution method. After cultivated inPDA medium with8%NaCl, pH8.0for7days, the colony diameters of those strains ranged from1.0to5.9cm. These20strains were identified by morphological observation, ITS sequence analysis and TEFsequence analysis. The results showed that,13strains belong to Trichoderma harzianum,3strainsbelong to Trichoderma longibrachiatum and2strains belong to Trichoderma brevicompactum and2strains belong to Trichoderma atroviride.2. Pythium aphanidermatum ACCC38064, Phytophthora parasitica var. nicotianae ACCC38064,Alternaria alternata ACCC38066were used as pathogens to evaluate the antagonistic effect ofTrichoderma strains by dual culture and fermentation liquid inhibition testing.10strains were selectedfor pot incubation experiment. It was found that tobacco seedlings had no disease after incubated withAlternaria alternata ACCC38066, these10strains all had a certain control effect to the tobaccodamping-off and tobacco black shank. Among them No.17strain had the best control with the controlrate of75%to tobacco damping-off and100%to tobacco black shank. Followed by No.7strain andNo.4strain. No.16strain had the worst incubated effect.3. The pot trial was conducted to study the effects of Trichoderma strains which had a bettercontrol to tobacco diseases on the growth of tobacco seedlings. The results showed that these followingstrains could improve tobacco stem and leaf growth, No.1strain, No.7strain, No.11strain and No.14strain. While No.1strain, No.7strain, No.11strain, No.14strain and No.18strain had a better growthpromoting effect on tobacco root. Three Trichoderma strains No.1, No.7and No.14were chosen for potexperiments in greenhouse to test their potential in promoting tobacco and cucumber growth byalleviating negative effect of salinity. The results indicated that No.1strain could improve the survivalrate of tobacco seedlings, increase the soluble protein content and peroxidase (POD) activity in tobaccoleaves, and decrease the malonyldialdehyde (MDA) content of tobacco leaves. All of these threeTrichoderma strains could improve the survival rate of cucumber seedlings under salt stress conditionand promote cucumber root growth. No.1strain could improve peroxidase (POD) activity in cucumberleaves significantly.4. Three pairs of Trichoderma strains which belong to the same species and had different salttolerant ability were used to carry out salt tolerant mechanisms study. It was found that, in transferringtest at different NaCl concentration gradient, the method of transferring strains from PDA medium with low NaCl concentration to high NaCl concentration used in this suudy could not induce the improvingof their ability to salt tolerance. FTIR determination of these three pairs of Trichoderma strains showedthat, for Trichoderma longibrachiatum and Trichoderma atroviride, content of various organiccompounds, proteins, lipids, phosphate compounds and polysaccharides in strains with low salt tolerantability were higher than the strains with high salt tolerant ability. On the contrary, those substances inTrichoderma harzianum with low salt tolerant ability were lower than the strains with high salt tolerantability. Trehalose, total free amino acids, glutamic acid, alanine and proline content of two Trichodermalongibrachiatum strains under different salt stress conditions were determined. The results indicated that:Among0.25%-1%NaCl stress range, the trehalose content of two Trichoderma strains were all on therise. The trehalose content of No.6strain with lower salt tolerance ability increased slowly and wasalways lower than the strain cultivated in PDA liquid medium with no NaCl. The trehalose content ofNo.7strain with higher salt tolerance ability increased quickly. In addition, trehalose content of No.7strain up to maximum when incubated in PDA liquid medium containing1%NaCl and was higher thanthe strain cultivated in PDA liquid medium with no NaCl. Besides, regardless of the presence of NaClstress, trehalose content of No.7strain was always higher than No.6strain. Contents of total free aminoacid, glutamic acid, alanine and proline in Trichoderma strains cultivated in PDA liquid mediumcontaining1%NaCl were increased compared to strains cultivated in PDA liquid medium with no NaCl.Free amino acid contents of No.6strain with relative lower salt tolerance ability increased more thanthat of No.7strain which had higher salt tolerance ability. Regardless of the existence of salt stress, totalfree amino acid, glutamic acid, alanine and proline contents of No.6strain were significantly higherthan No.7strain.