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Abstract 6.SUMMARY AND CONCLUSION Potato (Solanum tuberosum L.) is the fourth main crop in the world after wheat, rice, and maize. Since the past two decades, the potato sector in Egypt has undergone rapid changes in potato industry. However, large amount of potato are kept under ordinary storage conditions. This frequently lead to many problems among which is tuber dry rot disease which causes a greater loss of potatoes than any other post-harvest diseases. Assessing disease status of stored potatoes allows for better disease management. Disease control strategies could eventually integrate use of alternative methods like physical. Safe chemical compounds and microbial antagonists. The objectives of the research reported here were: (i) to isolate the fungal species causing dry rot and determine the extent of co-ioculation of such isolates on storability of tubers. (ii) to identify specific treatments to suppress dry rot. Results could be summarized as follows: 1. The three potato cultivars (Desriee, Annabelle, and Spunta), collected from El-Deer village, Sheibin El- Kanater, Kalyubia Governorate during winter season 2012, and stored in pored cartoon boxes under room temberature and refrigerator for two monthes showed dry rot disease during storage. 2. All stored potato tubers of cultivar Annabelle were rotted with appearance of white mycelial mats; while tubers of Spunta cv showed 50% of rot signs and 10% of Desiree cv. tubers showed various rot degrees when stored in pored carton boxes under room temperature, for 2 months. SUMMARY AND CONCLUSION Ola B. Abd El-Hafez, M.Sc., 2014 76 3. Twenty- two fungal isolates were isolated included five genera, being (Fusarium, Penicillium, Altenaria, Drechslera, and Chaetomium). 4. Frequency of isolated the fungi from the rotted potato tubers indicated that 64% of isolated fungi belong to Fusarium spp, Penicillium sp. (14%) , Drechslera sp.(4%) , and Chaetomium sp. (4%). 5. Only one isolate of each Cyanobacteria , Fusarium sp. and Bacillus sp. were isolated from soil-adhered to potato tuber. 6. Identification of isolated Fusaria indicate that they belong to three species i.e. F. solani, F. sambucinum and F. oxysporum. Frequency of these species indicates that 86% belong to F. solani, 7% belong to F. sambucinum and 7% belong to F. oxysporum. 7. The pathogenicity of 14 isolates of Fusarium spp. showed varied reactions on potato tuber discs Spunta cv., and F. sambucinum (F4) was more pathogenic compared to F. solani and F. oxysporum. 8. Three Penicillium isolates were more vigorous on potato tubers in comparison to isolate of F. solani. Subculturing of Penicillium sp. isolates caused losses of their pathogencity on potato tuber discs. Therefore, pectinase and cellulase activity of Penicillium cultured on Pectin or CMC indicated the ability of the tested isolate to hydrolyze both pectin or CMC 9. Alternaria sp., Drechslera sp., Cheatomium sp. were not pathogenic to potato tuber discs of Spunta cultivars. SUMMARY AND CONCLUSION Ola B. Abd El-Hafez, M.Sc., 2014 77 10. The co-inoculation between F. solani and Penicillium sp., Alternaria sp., and Drechslera sp. were tested on the dry rot disease. 11. The co-inoculation between Fusarium sp. and Penicillium sp. caused that the sporulation of Penicillium sp. was more than the control rotted discs although it lost its pathogenicity. 12. The co-inoculation between F. solani and both fungal isolates Drechselra sp. and Alternaria sp. had no significant effect on dry rot., and it showed reduced in the sporulation of the first fungi, and the sporulation of the second and the third fungi were completely absent. 13. Chloroform soil extract greatly suppressed all figures of dry rot disease for F. solani (2), while it suppressed the rot completely in the in the weak isolates (IC4, IE8lab). 14. All figures of disease due to severely pathogenic isolate were non affected due to the presence of Bacillus sp., while disease caused by moderately and weak Fusarium isolate significally affected and all figures of disease were decreased to a very great extent. 15. The culture filtrate of cyanobactria (Nostoc sp.) has a less effect on dry rot disease, and it suppressed the sporulation. The polar fraction of culture filtrate have not any affect on dry rot disease and the non polar fraction effected on all figures of dry rot in moderately and weak isolates. 16. The exposure of potato tuber discs to warm shock (42ºC for 5 min.) and cold shock (10 ºC) before inoculation with F. solani led to significantly decrease all disease figures 17. Four chemical compounds (N-acetylcysteine, chitosan, hydrogen peroxide, and calcium chloride) were used for studying their effect on the dry rot disease. SUMMARY AND CONCLUSION Ola B. Abd El-Hafez, M.Sc., 2014 78 18. N-acetylcysteine (0.04%) reduced the weight of the rotted tissues and fungal sporulation 19. Chitosan (1%) significantly reduced all figures of disease severity 20. H2O2 (4%) significantly effected on all figures of disease while the all concentration of H2O2 effected on the sporulation of the disease 21. CaCl2 especially at 1% or 2% significantly reduced percentage of the rotted area and the weight of rotted tissues. All tested concentrations significantly suppressed F. solani sporulation especially 1%. 22. The three tested agents i.e. warm water (42ºC), acetylcysteine at 0.4mg/ml and chitosan increased the PO activity over control (non-treated inoculated discs). Meanwhile, the other three tested agents reduced PO activity below control discs i.e. cold water (10ºC), H2O2 (4%) and calcium chloride (1%). |