2.10.18
BIOLOGICAL ACTIVITIES OF TRICHODERMA SPP. AGAINST MACROPHINIA PHASEOLINA, THE CAUSE OF CHARCOAL ROT OF SOYBEAN

MA AWAD1, M NAZIM1, MZ EL-SHANAWANI1 and MF SALEM2

1Faculty Of Agriculture, Minufiya University, Shibin El-Kom, Egypt; 2Plant Pathology Institute, Agricultural Research Centre, Giza, Egypt

Background and objectives
Macrophomina phaseolina (Tassi) Goid, the causal organism of charcoal rot of soybean, is a widespread soil-borne pathogen in the Egyptian soil. It infects the germinating seeds and at seedling stage causing pre- and post-emergence damping off. It also infects the roots of plants at the later stages of growth causing charcoal rot. The regular method for controlling this pathogen is by seed dressing with fungicides. The aims of the present work were to suppress the pathogen biologically using different isolates of Trichoderma spp. to avoid the harmful effect of chemicals and shed light on the mode of action(s) of Trichoderma spp. in degrading the pathogen structures.

Materials and methods
The interactions between isolates ofTrichoderma spp. and M. ;phaseolina were studied in dual cultures. The biocontrol effects between these isolates were studied in pots. The interaction was also studied using electrophoresis methods, gel filtration technique and transmission electron microscopy.

Results and conclusion
In the dual cultures, inhibition, antagonism, hyperparasitism and overgrowth were found to reduce and affect the growth and sclerotial production of the pathogen. Trichoderma hyphae contacted and coiled around the M. ;phaseolina hyphae and parasitized them [2]. There were considerable differences in the suppressive activity of sclerotial production of M. ;phaseolina by Trichoderma spp. pseudokoningii was more effective than the other Trichoderma spp. Isolate No. 3 of T. ;hamatum was the most suppressive for sclerotial numbers among the Trichoderma isolates tested. The application of the biocontrol agents reduced seedling damping-off and charcoal rot disease incidence. T. ;harzianum was the most effective biocontrol agent on the two cvs. Crowford and Cutler 71, while T. ;thamatum was most effective on cv. Clark, followed by T. ;pseudokoningii. Six isolates of the three Trichoderma spp. were tested for their production of chitinolytic enzymes. Each isolate of each species produced two chitinolytic enzymes i.e.chitobiosidase and endochitinase. Two protein bands were observed in the purified culture filtrates using gel filteration representing different levels of N-glycosylation. The molecular weights of the chitobiosidaase and endochitinase were 40 ;kDa and 41 ;kDa,respectively. Degradation of cell wall of M. ;phaseolina was carried out using transmission electron microscope. Bursting and distortion of scierotial and pycnidial walls were observed. Both enzymes had digestive and lytic effects on both sclerotial and pycnidial walls. The hyphal cells and chitin microfibrils were digested and lysed as a reflection to enzyme addition [1]. The chitin was broken down gradually and finally, the fungus cells collapsed with retraction of the plasma membrane and cytoplasm aggregation.

References
1. Benhamou N, Chet L, 1993. Phytopathology 83, 1062-1071.
2. Gangopadhyay D, Wyllie TD, Luedders VD, 1970. Plant Disease Reporter 54, 1088-1091.