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Abstract
SUMMARY
Soybean (Glycine max L.) is one of the important legume crops in Egypt and many parts of the world, which contain high value of protein and oil. However, soybean seedlings are subjected to the attack by numerous pathogens causing damping-off and root rot diseases during the germination which reduce considerable losses in quantity and quality of the crop.
The present investigation was planned to survey soybean fungal damping-off diseases, isolate and study the pathogenicity of the fungi most frequently and virulent pathogens associated with soybean (Glycine max L.) of many cultivars. The investigation includes also the study of the effect of some biological agents and extracts in addition to Rhizolix-T fungicide. Effect of diseases severity on protein, oil, sugar contents, hydrolysis enzymes and phenolic compounds of soybean seeds were also examined. Changes in protein patterns extracted from soybean cultivars due to the infection by R. solani (with sodium dodecyel sulphate-polyacrylmide gel Electrophoresis (SD-PAGE). Similarity between protein patterns of soybean cultivars and virulent isolate of R. solani. Histopathological investigations were also detected in order to observe the changes in interior tissues of soybean due to the causal pathogens.
The results of this study could be summarized in the following:
6.1. Survey of soybean damping-off diseases :
The data of survey revealed that the Crawford cultivar was the most affected in both governorates during 2003, 2004 and 2005 growing season. The least affected was Giza 21 in both governorates during seasons 2003, 2004 and 2005. Giza 21, Giza 22 Giza 111 and Crawford cultivars was intermediately affected in both governorates during season 2003, 2004 and 2005 within each governorates was variation in infected index not significantly in all seasons for one cultivar.
6.2. Pathogenicity tests :
Soybean damping-off causal agent isolated from soybean roots collected from different location in Alexandria and Behera, purified and identified as: R. solani, F. solani and P. debaryanum. The pathogenicity tests proved that all the tested fungi were pathogenic and able to produce pre-emergence damping-off (PRD), post-emergence damping-off (PTD) in different degree on soybean cultivars namely; Giza 21, Giza 22, Giza111 and Crawford. The highest PRD values were obtained with Crawford cultivar inoculated with R. solani, F. solani and P. debaryanum. (15.22, 55.09 and 56.22%). The least infect values less than 2.07, 3.05 and 5.03 were obtained on Giza 21 cultivar. The highest (PTD) incidence ratios were obtained by R. solani, F. solani and P. debaryanum on Crawford cultivar (67.33, 24.91 and 32.31) Whereas, the least infection values less than (4.15, 1.07 and 4.13) were obtained on Giza 21 cultivar, the moderately (PRD), (PTD) values were obtained with Giza 111 cultivar (5.05, 7.09 and 16.39 PRD), (12.67, 6.16 and 5.97 PTD) by R. solani, F. solani and P. debaryanum.