Heba I. Mohamed

Impact of secondary metabolites and related enzymes in flax resistance and/or susceptibility to powdery mildew

Changes in various physiological defenses including secondary metabolites, proline, total soluble protein and antioxidant enzymes were investigated in leaves and stems of 18 flax lines either resistant or susceptible to powdery mildew. The results showed that the total alkaloids content in flax stems was significantly increased in resistant lines when compared with resistant parent, but significantly decreased in susceptible lines and susceptible parent when compared with resistant parent. Stems of the resistant flax lines had a higher content of total phenols than susceptible ones upon pathogen challenge. Infection with powdery mildew significantly increased peroxidase, polyphenol oxidase and catalase activities in leaves of flax lines when compared with either resistant or susceptible parents as well as proline content. This increase was much pronounced in tolerant lines than resistant lines. Total soluble protein content in flax leaves increased significantly in resistant lines when compared with resistant parent but decreased significantly in susceptible lines when compared with resistant parent.

Association of oxidative stress components with resistance to flax powdery mildew

Field trials were conducted in 2008/2009 and 2009/2010 growing seasons at Giza Agricultural Research Station to evaluate powdery mildew (PM) severity on nine flax cultivars. Tested cultivars could be classified into five distinct groups, i.e., highly susceptible (Corland and C.I. 2008), susceptible (Giza 7 and Marshall), moderately susceptible (Cass), moderately resistant (Dakota, Koto and Wilden) and resistant (Ottowa 770B). They showed considerable variation in PM severity ranging from 8.1 on Ottowa 770B to 97.0% infected leaves/plant on Cortland. Total soluble proteins, total phenols, peroxidase, polyphenoloxidase, ascorbic acid, tocopherol and malondialdehyde were determined in infected leaves of the tested cultivars. Pearsons correlation coefficient was calculated to measure the degree of association between PM severity and each biochemical component. All components showed significant (P<0.05) or highly significant (P<0.01) negative correlation with PM severity except MDA, which showed positive correlation (P<0.01). The results of the present study suggest that phenols and MDA in infected leaves could be used to assist the screening of resistant plants at early stages of powdery mildew development.

Examination of Correlations Between Several Biochemical Components and Powdery Mildew Resistance of Flax Cultivars

A field trial was conducted in 2009/2010 and 2010/2011 growing seasons at Giza Agricultural Research Station to examine correlations between some biochemical componets and powdery mildews (PMs) resistance in flax cultivars. Nine flax cultivars could be divided into five distinct groups, i.e., highly susceptible (Cortland and C.I. 2008), moderately susceptible (Giza 7, and Marshall), moderately resistant (Cass), resistant (Koto, Dakota and Wilden), and highly resistant (Ottowa 770B). The cultivars showed considerable variation in PM severity ranged from 8.05 on Ottowa 770B to 97.02% on Cortland. Total soluble proteins, total phenols, antioxidant enzymes (peroxidase and polyphenoloxidase), ascorbic acid, tocopherol, and malondialdehyde (MDA), were determined in uninfected leaves of the tested cultivars. Pearson’s correlation coefficient was calculated to measure the degree of association between PM severity and each component. All components showed significant (P < 0.05) or highly significant (P < 0.01) negative correlation with PM severity except MDA, which showed positive correlation (P < 0.01). Linear regression analysis was used to evaluate the causal relationship between the biochemical components (independent variables) and PM severity (dependent variable). Coefficient of determination (R 2 ) values of the generated models ranged from 48.76 to 77.15%. Tocopherol, MDA, and proteins were the most important contributors to the total variation in PM severity as the R 2 values of their models were 71.78, 75.28, and 77.15%, respectively. The results of the present study suggest that tocopherol, MDA, and proteins in uninfected leaves can be used as biochemical markers to predict PM resistance in flax.

Changes in antioxidants potential, secondary metabolites and plant hormones induced by different fungicides treatment in cotton plants

The use of fungicides for an effective control of plant diseases has become crucial in the last decades in the agriculture system. Seeds of cotton plants were treated with systemic and contact fungicides to study the efficiency of seed dressing fungicides in controlling damping off caused by Rhizoctonia solani under greenhouse conditions and its effect on plant growth and metabolism. The results showed that Mon-cut showed the highest efficiency (67.99%) while each of Tondro and Hemixet showed the lowest efficiency (31.99%) in controlling damping off. Rhizolex T, Mon-cut and Tondro fungicides caused significant decrease in plant height, dry weight of plant, phytohormones, photosynthetic pigments, soluble sugars, soluble proteins, total free amino acids but caused significant increases in total phenols, flavonoids, antioxidant enzymes, ascorbic acid, reduced glutathione, MDA and hydrogen peroxide as compared with untreated plants. On the other hand, the other fungicides (Maxim, Hemixet and Flosan) increased all the above recorded parameters as compared with untreated plants. Our results indicated that the fungicides application could be a potential tool to increase plant growth, the antioxidative defense mechanisms and decreased infection with plant diseases.

Physiological role of exogenous nitric oxide in improving performance, yield and some biochemical aspects of sunflower plant under zinc stress

The present study was undertaken to examine the possible roles of sodium nitroprusside in protection against oxidative damage due to zinc toxicity in sunflower plants. Physiochemical parameters in sunflower plants exposed to Zn2+ (100, 200 and 300 mg/kg soil) alone or combined with SNP were measured. The results showed that excess of Zn decreased plant growth, seed yield components and photosynthetic pigments content. On the other hand, Zn stress increased the level of non-enzymatic antioxidants (ascorbic acid and reduced glutathione) and enzymatic antioxidants (superoxide dismutase, ascrobate peroxidase and glutathione reductase), coupled with the appearance of novel protein bands. Furthermore, Zn stress increased Zn content in roots and shoots. The amounts of Zn in roots were higher than shoots. A marked increase in total saturated fatty acids accompanied by a decrease in total unsaturated fatty acids was observed. Exogenously application of SNP (20 μM) increased growth parameters, photosynthetic pigments content, ascorbic acid and glutathione contents, antioxidant enzyme activities and the quality of the oil in favour of the increase of unsaturated fatty acids. Moreover, SNP application increased Zn concentration in roots and inhibited Zn accumulation in shoots. Therefore, it is concluded that SNP treatment can help reduce Zn toxicity in sunflower plants.

Biochemical and Ultrastructural Changes of Some Tomato Cultivars after Infestation with Aphis gossypii Glover (Hemiptera: Aphididae) at Qalyubiyah, Egypt

Tomato plants are severely infested with Aphis gossypii in all over the world. The present investigation aims at evaluating effects of tomato leaf biochemical components as well as leaflet surface physical features on the susceptibility of five tomato cultivars (Alissa, GS, Logan, Super Strain B and Andos). Results clearly indicated significant differences among the five tested tomato cultivars according to their susceptibility to A. gossypii infestation. In addition, the cultivars Logan and Andos are the most susceptible, while Super Strain B and Alissa cultivars showed moderate resistance. The GS cultivar, finally, was the most resistant one. Photosynthetic pigments, biochemical components and antioxidant defense enzymes activity were negatively affected by infestation. Moreover, the density and length of leaflet non-glandular trichomes negatively effect on the population density of A. gossypii, while this was not the case with glandular trichomes. From these results, the susceptibility of tomato cultivars on the basis of these results in the integrated aphids management programs.ZusammenfassungTomatenpflanzen sind in der ganzen Welt stark mit Aphis gossypii befallen. Das Ziel dieser Untersuchung war es, die Auswirkungen von biochemischen Komponenten von Tomatenblättern wie auch physische Merkmale von Blättern auf die Anfälligkeit durch fünf Tomatenkultivaren auszuwerten (Alissa, GS, Logan, Superstamm B and Andos). Die Ergebnisse zeigten wesentliche Unterschiede zwischen den fünf Tomatenkultivaren bei der Anfälligkeit durch A. gossypii befallen zu werden. Kultivare Logan und Andos waren am empfänglichsten, während die Kultivare Superstamm B und Alissa eine mäßige Resistenz zeigten. Der GS-Kultivar war der am stärksten resistente. Photosynthetische Farbstoffe, biochemische Komponenten und antioxidative Abwehrenzyme wurden durch den Befall negativ beeinträchtigt. Darüber hinaus beeinträchtigte die Dichte und Länge von nicht-glandulären Blatt-Trichomen die Populationsdichte von A. gossypii negativ, wohingegen dies nicht der Fall bei glandulären Trichomen war. Diese Ergebnisse in Bezug auf den Befall von Tomatenkultivaren sollte bei integrierten Aphid-Management-Programmen nicht außer Acht gelassen werden.

Physiological and molecular genetic studies on two elicitors for improving the tolerance of six Egyptian soybean cultivars to cotton leaf worm

Cotton leaf worm (Spodoptera littoralis) is considered one of the most destructive agricultural pests in Egypt. Six soybean cultivars (Giza-21, Giza-22, Giza-35, Giza-82, Giza-83 and Giza-111) were grown under natural infection with cotton leaf worm. The effect of two elicitors, methyl jasmonate and sodium nitroprusside on enhancing the ability of susceptible cultivars to tolerate (Spodoptera littoralis) was studied. Giza-35 and Giza-111 showed tolerance performance under natural infection compared to Giza-22 and Giza-82 as sensitive ones, while Giza-83 and Giza-21 showed moderate tolerance. Both treatments positively affected seed yield and its components and fatty acid composition. Extracted fatty acids showed variable changes in treated plants compared with the untreated controls. Plants treated with the two elicitors showed an increase in Linoleic acid and Linolenic acid fatty acids and decrease in Palmitic acid and Palmitolic acid content. Treatment with methyl jasmonate was found to be more effective than sodium nitroprusside and enhanced resistance of the susceptible cultivars. Eight IRAP and iPBS retrotransposon-based markers were used to detect genetic differences among studied soybean cultivars and to develop molecular genetic markers for cotton leaf worm infestation. The technique successfully identified soybean genotypes in addition to nineteen molecular markers related to soybean tolerance.