الفهرس 
ACKNOLEDGEMENTS
Susceptibility of sorghum cultivars to cereal aphidsOnly 14 pages are availabe for public view
 |  | from | 219 |  |  |
| | | from | 219 | | |
Abstract
The headlines of the current study were categorized mainly into three main research topics. The first research line focused on ecological studies on the main cereal aphids infesting different cultivars of cereal plants in Assiut. This was associated with some physiological studies addressing the physiological changes in the most widely distributed cereal aphid R. maidis in response to feeding on different cultivars of cereal plants. The second research line included molecular sequencing of COI gene in R. maidis samples collected from wheat, barley, sorghum and maize. Furthermore, toxicity of some entomopathogenic fungi was addressed for the potential use as biopesticides.
1- Ecological and physiological studies
The present study was undertaken to address some ecological and physiological parameters related to the biology of the main aphids infesting some cultivars of four cereal plants; barley, wheat, sorghum and maize in Assiut governorate. Five cultivars of each plant were selected in these studies. The barley cultivars used included Giza 123, Giza 124, Giza 125, Giza 132 and Giza 2000 while wheat cultivars included Sids1, Sids12, Giza 168, Shandauel 1 and Gemiza 11. Sorghum cultivars included Local (Baldi), Giza 15, Dorado, Hourse and Sphinx. Maize cultivars included Local (Baldi), Unique 6, Unique 81, Unique 131 and Triple 310.
Field survey studies through winter and summer growing seasons of 2017 identified three aphid species belonging to order Homoptera and family Aphididae infesting the above mentioned cultivars. These species were the corn leaf aphid (R. maidis), the oat bird cherry aphid (R. padi) and the green bug (S. graminum). Data showed that R. maidis seems to be the most important economic pests infesting the tested crops as indicated by the highest value of dominance and abundance degrees. In general, it was found that all the barley and wheat cultivars infested with aphid during mid- January and disappeared during the second half of March. Also, aphid population began to infest sorghum and maize cultivars during the end of August and vanished at mid-October.
Results indicated that some cultivars of cereal crops exhibited resistance pathways to aphid infestation. Barley cultivars; Giza 2000 and Giza 124, wheat cultivars; Shanduel 1 and Sids 1, sorghum cultivar; Local and maize cultivar; Unique 81 were the most resistant to aphid infestation. Our results recommend the farmers to cultivate the resistant cultivars for many years to increase their resistance and avoid aphid infestation.
Physiological results showed that different cultivars of cereal plants affected the antioxidant system, lipid and carbohydrate contents and the enzymes involved in their digestion in R. maidis suggesting that the cultivation of right field crops can manage aphids that attack them via targeting some metabolic pathways.
2- Molecular sequencing of R. maidis COI gene
Partial sequencing of cytochrome oxidase I gene was performed on the main aphid infesting cereal plants in Assiut (R. maidis) using samples collected from the four cereal plants listed above. The main purpose of this analysis was to answer a research question on whether R. maidis is present on summer and winter cereal plants in different biotypes. These host plants are variable in the cultivation temperature which suggests molecular adaptation of R. maidis to survive in wide range of temperature and humidity. Sequencing data analysis suggested at least 5 different polymorphs of R. maidis are present attacking cereal plants. These polymorphs may represent one or more biotype.
3- Toxicity of entomopathogenic fungi on R. maidis
The lethal concentrations of some entomopathogenic fungi were calculated to address the possibility of using them as biopesticides. Using some entomopathogenic fungal strains suggested that the entomopathogenic, M. anisopliae is more suitable and can be used as potential biocontrol agent under field experiments for the management of the corn leaf aphid. Also, results indicated that mortality of adult aphids increased with increasing the conidial concentrations of fungal strain and the time placed after treatment.