الفهرس 
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Abstract
Results of the present work can be summarized as follows:
I. Isolation, Identification and Pathogenicity tests of the causal pathogen(s) of pokkah boeng disease of sugarcane:
1) Forty one isolates of fungi belongs to Fusarium species isolated from diseased samples showing pokkah boeng symptoms collected from four different Agriculture Research Stations located at four Governorates (Asswan, Louxor, Sohag and Minia) of Upper Egypt were isolated. All the tested fungal isolates were pathogenic on G.T. 54-9 sugarcane variety and produced typical symptoms of pokkah boeng disease. They differed in their virulence from high to weak. The highest disease severity of fungi was recorded by isolates K2 and K5 (80.00%) followed by isolates K10 and K3.
2) from the obtained isolates, only ten isolates (K2, K5, K10, K3, E7, S5, E2, E5, S1 and S8) which gave the highest disease severity were selected for identification using cultural, morphological and microscopical characteristics of spores and mycelia. Isolates S1, S5, E2, E5, K2, K3, K5 and K10 were Fusarium subglutinans (Wollenweber& Reinking) Nelson et al., However, isolates S8 and E7 were Fusarium verticillioides (Saccardo) Nirenberg and Fusarium proliferatum (Matsushima) Nirenberg, respectively.
3) Frequencies of the isolated Fusarium species are varied in different tested locations. Fusarium subglutinans was the highly frequent species followed by Fusarium verticillioides and Fusarium proliferatum. Frequency percentage of Fusarium subglutinans was 80% however frequency of Fusarium verticillioides and Fusarium proliferatum was 10%, each. Fusarium subglutinans was associated with the disease at El-Mattana, Kom-Ombo and Shandweel locations. In addition, Fusarium verticillioides and Fusarium. proliferatum are present in Shandweel and El-Mattana, respectively.
II. Molecular variability existed among Fusarium species associated with pookah boeng disease of sugarcane:
1) Genetic variability and polymorphism within and among isolates of different Fusarium spp. isolated from three different climatic regions in Egypt, El-Mattana (E), Kom-Ombo (K) and Shandawel (S) were estimated using nine RAPD primers. All the tested nine RAPD primers were found to be highly reproducible and produced a total of 136 DNA fragments of which 131 (96.32%) were polymorphic. The highest number of amplified DNA fragments was detected for the primer OPM07 (19 bands), while the lowest number was amplified with the primer OPA14 (7 bands). Isolate K5 displayed the highest number of DNA fragments (63 bands), while S8 revealed the least number of bands (43 bands).
2) Unique DNA fragments with different sizes were detected in particular isolates but not in the others using different primers. The largest number of RAPD-PCR specific markers was scored for isolate K2 (11 markers) followed by isolate S8 (9 markers), while the lowest specific markers (1 marker) was scored for isolate E2. Thirty nine isolates -specific markers were detected indicating that they could be used as markers for all studied isolates, except isolates K5 and K10.
3) These results show that there is a considerable genotypic variability among isolates belonging to the tested three Fusarium spp. Positive DNA markers were detected for Fusarium species isolated from EL-Mattana region (four markers) while only one marker detected for Fusarium spp. isolated from Kom-Ombo region which could be used as markers for identities of Fusarium spp. isolated from such regions. No specific markers characterize Fusarium spp. isolated from Shandaweel region.
4) DNA fragment with molecular size 474bp was detected only in K2 and K5 which could be used as positive marker for high disease severity.
III. Evaluation of certain sugarcane varieties to infection with pokkah boeng disease and effect of the disease on growth of sugarcane plants and quality of juice under greenhouse conditions:
1) The tested sixteen sugarcane varieties were susceptible to infection with K2 and K5 isolates of the pathogen with different degrees of susceptibility. In the two tested seasons (2010/2011 and 2011/2012), the G. T. 54-9 and G. 2004-32 varieties show high susceptibility to both isolates followed by G. 2003-47, G. 2003-3, G. 1999-103 and G. 1998-28 then other tested varieties. However, G. 2001-79 and G. 2000-176 varieties proved to be moderately susceptible to pokkah boeng disease. Concerning virulence of the isolates, K2 isolate caused higher disease severity than K5 isolate, on the tested sugarcane varieties in both tested seasons.
2) Concerning the effect of infection with fungal pathogen isolates on number of tillers/plant under pathogen stress it was observed that the number of tillers/plant was increased by two folds in infected plants with K2 or K5 isolates in both seasons compared with non- inoculated plants.
3) Compared with non-inoculated control plants in first and second seasons, the infection of different sugarcane varieties with both K2 and K5 isolates of the fungal pathogen significantly decreased the number of internodes/plant.
4) The stalk length of sugarcane plants was significantly reduced by infection with fungal pathogen in the most of tested sugarcane varieties. The greatest reduction of stalk length of sugarcane plants was recorded in G. 2003-3 variety while, the least reduction of stalk length was recorded in G. 2000-176 variety in first and second seasons, respectively.
5) Under artificial infection with K2 or K5 isolates of the pathogen, the stalk diameter of sugarcane markedly decreased by 20.21 and 13.50% in the first season, and by 24.3 and 18.10% in the second season. The stalk diameter of cane was lower in plants infected with K2 than in plants infected with K5 in first and second seasons, respectively.
6) Although, the Brix percentage in juice of sugarcane plants decreased in plants infected with K2 or K5 isolates of F. subglutinans in comparison with un-infected control plants, the effect of both isolates in Brix percentage in first and second seasons was similar.
7) In the both tested seasons, infection with the fungal pathogen markedly decreased sucrose percentage in juice of the tested sugarcane varieties. Although, the sucrose content of juice decreased after infection with both fungal isolates (K2 and K5) in the tested seasons compared with un-infected plants, isolates K5 caused the highest reduction compared with K2 isolate.
8) The purity percentage of juice of sugarcane plants infected with K2 or K5 isolates of the pathogen was strongly decreased by 15.85% and 8.47% and 29.53% and 27.74% in plants infected with K2 and K5 isolates compared with non-infected plants in the first and second seasons, respectively. Although, the purity percentage in juice of sugarcane was lower in infected plants than in non-infected plants, insignificant differences were recorded between the effect of K2 and K5 isolates on purity percentage in both seasons.
9) Compared with non-infected plants the pol percentage significantly decreased in plants infected with the pathogen isolates in both tested seasons. Insignificant differences between K2 and K5 isolates in their effect on pol percentage were observed in the first season. However, in second season, K5 isolate of the pathogen caused higher reduction of pol percentage in sugarcane plants than K2 isolate.
10) With respect to the effect of fungal pathogen isolates on sugar recovery percentage, data showed that significant differences presented between the effects of both isolates on sugar recovery percentage in both tested seasons. Furthermore, the K2 isolate caused the higher reduction of sugar recovery percentage than the K5 isolate, in first season. Contrary, the K5 isolate caused the higher reduction of sugar recovery percentage than the K2 isolate in second season.
11) Reducing sugar percentage in sugarcane juice was significantly increased after infection with K2 and K5 fungal isolates of F. subglutinans,in both seasons. Although, the reducing sugar percentage was higher in infected sugarcane plants than in non-infected plants in both seasons, insignificant differences between K2 and K5 isolate in their effect were observed in the second season.
IV. Effect of foliar fertilization with certain microelements (Zn, Mn and Fe) on severity of pokkah boeng, growth of sugarcane plants and quality of juice under field conditions:
1) Under artificial inoculation with K2 isolate of the pathogen in 2010/2011 and 2011/2012 seasons, foliar spray of G.T. 54-9 sugarcane variety with the three microelements (Zn, 100 mg/L; Mn, 150 mg/L; and Fe, 150 mg/L) separately or in combination significantly reduced pokkah boeng disease severity on sugarcane plants compared with untreated ones. However, when each microelement was applied separately the disease severity of pokkah boeng on sugarcane plants was reduced less affected compared to combined microelements treatment. Also, the disease severity decreased with increase number of sprays. Three foliar sprays caused the highest reduction of disease severity compared with two and one sprays, in both seasons.
2) Spraying sugarcane plants with tested micronutrients separately or in combination increased number of internodes/plant of sugarcane plants. Number of sprays of microelements gave a significant effect in increasing number of internodes/plant compared with control treatment in both seasons. Spraying sugarcane plants with three sprayers of the tested microelements gave the highest number of internodes/plant, while the lowest internodes/plant was found in sugarcane plants treated with one spray of microelements in the first and second season.
3) Foliar spray with the tested microelements significantly increased stalk length of sugarcane plants in first and second seasons, compared with untreated control. Also, the stalk length of sugarcane plants increased with increase of number of sprays in both seasons. Whereas, the foliar spray three times with each microelements separately or in combination was higher than in plants sprayed one or two times.
4) Stalk diameter of plants increased in treated plants with foliar spray of microelements alone or in combination compared with untreated plants in the two seasons. The combined fertilizer treatment gave the highest stalk diameter compared with the all separate microelements in both seasons. In general, increasing the number of sprays from one to three times gave the highest stalk diameter in both seasons compared with the one or two sprays.
5) Spraying sugarcane plants with the tested microelements (Zn, Mn and Fe) either separately or in combination had a significant effect in increasing the net cane yield (tons/fed) in both seasons. In general, the net cane yield (tons/fed) of sugarcane plants treated with combination of microelements was higher than in plants treated with each single microelement. The results also showed that increasing the number of sprays from one up to three sprays with microelements increasing net cane yield (tons/fed.) in the two tested seasons. Spraying sugarcane plants three times with each tested microelements exhibited the best net cane yield (tons/fed.) followed by two and one sprays in the two tested seasons.
6) Foliar spray of sugarcane plants with microelements separately or in combination significantly raised the values of Brix percentage in both seasons. Compared with water-treated plants (control), spraying sugarcane plants with the mixture of microelements increased the Brix percentage of sugarcane plant juice followed by Zn and Mn microelements in the first season, and followed by Zn microelement in the second season. In both seasons, the values of Brix percentage tended to increase by increasing number of sprays of microelements. Spray sugarcane plants with tested microelement alone or in combination with others increasing significantly sucrose percentage in juice of sugarcane plants in both seasons. The sucrose percentage of sugarcane plants treated with combination of microelements was higher than that in plants treated with single microelements in both seasons. The sucrose percentage of sugarcane plants increased with increase of number of sprays, whereas, the foliar spray three times with microelement either separately or in combination was higher than one and two times sprays.
7) Purity percentage of the juice significantly increased in sugarcane plants treated with foliar spray of microelements either separately or in combination compared with untreated plants. Plants of sugarcane sprayed with combination of microelements gave the highest purity percentage compared with separately microelements application in both seasons. Increasing the number of sprays from one to three times increased purity percentage of sugarcane plants in both tested seasons.
8) Foliar spraying with the tested microelements either separately or in combination significantly increased the pol percentage of sugarcane plant juice compared with untreated plants in both tested seasons. The combination of the Zn, Mn and Fe microelements caused the highest increase of pol percentage than single application in the both tested seasons. Increasing number of sprays of microelements from one up to three sprays enhanced the pol percentage values in the both tested seasons.
9) Spray with each microelement either separately or in combination significantly increased the sugar recovery percentage in juice of sugarcane plants compared to untreated plants in both seasons. Sugarcane plants treated with combination of microelements exhibited the highest sugar recovery percentage of sugarcane plants. Increasing the number of sprays from one to three sprays increased the sugar recovery percentage of sugarcane.
10) Compared to untreated sugarcane plants, foliar spray with the microelements either separately or in combination significantly increased the sugar yield (tons/fed.) in both seasons. The sugar yield (tons/fed.) in sugarcane plants treated with combination of microelements was higher than in plants treated with each single microelement. The sugar yield (tons/fed.) of sugarcane plants increased with increasing the number of sprays of microelements, whereas, the foliar sprays three times with each microelement alone or in combination increased the sugar yield higher than one or two times applications.
11) Spraying sugarcane plants with microelements raised the values of reducing sugar percentage compared with that obtained in control treatment in both seasons. The greatest reducing sugar percentage was recorded in combination of microelements treatments followed by Fe alone in the first season, while in the second season, the heights reducing sugar percentage was recorded in combination of microelements and in separate application of Mn followed by Zn and Fe microelements. Increasing number of sprays with microelements from one to three sprays led to increase reducing sugar percentage in both seasons.