Zakaria A. Baka

Alternaria eichhorniae, a biological control agent for waterhyacinth : mycoherbicidal formulation and physiological and ultrastructural host responses

The bioherbicidal efficacy of different alginate formulations of Alternaria eichhorniae 5 (isolate Ae5), a virulent Egyptian isolate, was compared on waterhyacinth (Eichhornia crassipes). The fungus was formulated as alginate pellets containing mycelium alone, mycelium plus culture filtrate or culture filtrate alone. Each formulation was applied with and without a hydrophilic humectant (Evergreen 500). These formulations were evaluated for disease incidence (DI), and disease severity (DS). Maximum DS, but not DI, was obtained with the alginate pellets of mycelium plus culture filtrate. Alginate formulations supplemented with the hydrophilic polymer were more effective in promoting disease. Physiological changes associated with the treated waterhyacinth plants were determined 3, 6 and 9 days after treatment. Waterhyacinth plants treated with alginate pellets of mycelium plus culture filtrate of Ae5 had the lowest levels of pigments, carbohydrates and relative water content. Infection of waterhyacinth with Ae5 led to a significant increase in total phenols of leaves as compared to control. Penetration of waterhyacinth leaves by the fungus occurred only through the stomata, and the invading hyphae were located in the intercellular spaces of leaf tissues. Cytological changes noted in infected cells included changes in chloroplast, nucleus and mitochondria. Invagination of the plasma membrane, particularly at plasmodesmata was also noticed in infected cells. The associations between the infection process, the physiological disorder and the ultrastructure of infected leaves are discussed.

Kinetin and spermine mediated induction of salt tolerance in wheat plants: Leaf area, photosynthesis and chloroplast ultrastructure of flag leaf at ear emergence

Abstract The antagonistic effects of kinetin and spermine on stress imposed by seawater on leaf area, pigment, Hill reaction, 14CO2 fixation and chloroplast ultrastructure of wheat flag leaf were investigated. Irrigation of wheat plants by seawater at 25% caused marked decrease in leaf area, pigment content, Hill activity and photosynthetic efficiency of wheat flag leaf at ear emergence. Grain priming with kinetin, spermine or their interaction alleviated the adverse effect of seawater stress by stimulating leaf area expansion, pigment production as well as photosynthetic activity. From transmission electron microscopy micrographs, a continuous “end-to-end” distribution of regular (oval or elliptical) chloroplasts around the cells periphery was observed in flag leaf mesophyll cells of control wheat plants. Conversely for seawater-stressed plants, the irregular spherical chloroplasts appeared “bulbous” and discrete, the cells also displayed extensive but thin peripheral cytoplasmic regions devoid of chloroplasts. Grain presoaking in 0.1 mM kinetin caused the chloroplast of stressed wheat plants to be more regular, with organized membrane system, large starch grains and projections in the form of tails. Furthermore, ultrastructure analysis cleared that grain priming with spermine, either alone or in combination with kinetin, caused the chloroplast in flag leaf mesophyll cells of stressed wheat plants to be more regular in shape with more starch grains. The changes in pigment content and photosynthetic activity of flag leaf appeared to depend mainly on chloroplast ultrastructure and its numbers, showing a positive correlation between chloroplasts number and pigment content.

Changes in chlorophyll, polyamines and chloroplast ultrastructure of Puccinia striiformis induced 'green islands' on detached leaves of Triticum aestivum

Abstract Biochemical and ultrastructure features of ‘green islands’ were investigated using detached wheat leaves infected with the yellow rust Puccinia striiformis . Chlorophylls appear to culminate 10xa0d after inoculation at which point ‘green islands’ were fully developed. These changes were paralleled by an increase in spermidine and spermine content which play an important role in formation of ‘green islands’. Retention of chlorophyll was demonstrated in leaf tissues of wheat plants supplied with exogenous putrescine, spermidine and spermine. Putrescine was least and spermidine and spermine most effective in retarding loss of chlorophylls. Ultrastructural observation revealed that chloroplasts were regenerated in ‘green islands’ where many proplastids were detected. The regeneration of chloroplasts coincided with the high concentration of chlorophylls and polyamines particularly spermidine and spermine. The ultrastructural changes of chloroplasts in leaf cell containing infection structures were parallel to physiological changes.

Efficacy of seawater salinity on osmotic adjustment and solutes allocation in wheat (Triticum aestivum) flag leaf during grain filling

ratio in the flag leaves of both cultivars was observed. The capacity of osmotic adjustment was greater in younger leaves than in older ones particularly with higher concentration (25%) in both cultivars. Moreover, the production of both organic and inorganic ions tended to be higher in Sids-1 than in Gemmieza-9. Gemmieza-9 appeared to be more sensitive than Sids-1.Osmotic pressure of flag leaf sap appeared to depend mainly on proline, TSN, TSS, organic acids, glycerol and ions content, where there is a positive correlation between osmotic pressure and all of them.

Occurrence and morphology of Puccinia lagenophorae on Senecio glaucus in Egypt

Abstract Puccinia lagenophorae , a rust fungus originating from Australia and established in Europe since 1960 has been found for the first time in Egypt on Senecio glaucus . The fungus is described in detail with light and scanning electron microscopy. The possibility of using this species as a biological control agent was also discussed.

The effect of benomyl on growth and ultrastructure of two isolates of Phytophthora infestans from Egypt.

The effect of benomyl as a fungicide on the growth rate and ultrastructure of two isolates (P1319 and P623) of Phytophthora infestans is compared. Benomyl caused a concentration-dependent inhibition of the mycelial growth of both isolates. The isolate P1319 was found to be more sensitive to benomyl than the isolate P623. Ultarstructural studies confirmed these observations. The hyphae of isolate P1319 subjected to 100 and 500 ppm benomyl showed more severe changes in the cytoplasm than those of isolate P623. An increase in lipid bodies and vacuoles in the hyphal cytoplasm was the characteristic phenomenon after treatment with benomyl, particularly at a concentration of 500 ppm.

Shikimic and Salicylic Acids Induced Resistance in Faba Bean Plants against Chocolate Spot Disease

Surveys for faba bean chocolate spot disease covering 6 districts in Delta of Egypt were conducted. Out of these surveys, six isolates of the pathogen were obtained and purified using single spore technique. These isolates were identified as Botrytis fabae. All isolates were subjected to pathogenicity tests to determine the most aggressive one. All isolates appear to have the potency to cause chocolate spot disease, but the isolate from Sherbin was considered to be the most aggressive one and was selected for further studies. In vitro, the effect of provided phenolic compounds on inhibition of mycelia growth and the growth rate of B. fabae was investigated and arranged as follows: salicylic acid > Shikimic acid > shikimic acid+salicylic acid, as compared to control values. Furthermore, significant reduction in the disease incidence (%) and severity (%) were recorded in faba bean plants treated with salicylic acid followed by shikimic acid then their interaction. Botrytis fabae infection caused noticeable increase in the activity of defense enzymes (i.e., peroxidase, polyphenol oxidase and phenyl alanine ammonia lyase) in infected faba bean plants. In the majority of cases, the applied phenolic compounds induced additional increase in such enzymes than that sprayed with fungicide. This increment was concomitant with the increase in the endogenous total phenols, shikimic acid and salicylic acid content. In addition, the most effective treatment in enhancement faba bean resistance against B fabae infection was salicylic acid at 0.7 mM