The nematicidal effect of three marine algal, Ulva fasciata Delile (UF) (green algae), Corallina mediterranea, Corallina officinalis (red algae), extracts on egg hatching and second-stage juveniles (J 2 ) mortality of root-knot nematode (Meloidogyne incognita) in vitro compared to the nematicide activity of Oxamyl 24% SL (5 ml/l) was investigated. Results revealed that all treatments at the applied concentrations suppressed the egg hatching in 3 days. In details, the algal strain Ulva fasciata Delile extract showed the highest activity in decreasing the eggs hatchability after 3 days with 87%. Consequently, all treatments significantly increased the mortality of J 2 larvae after 12, 24, and 48 h compared to the control treated with distilled water. Under greenhouse conditions, all treatments in inoculated soils cultivated with tomato plants had reduced numbers of galls, egg-masses/plant, and the number of J 2 /250 g than the non-inoculated soil. The algal extract and the Oxamyl 24% SL (5 ml/l) increased the length and fresh weight of plant shoots and roots than the untreated. However, there were no differences in shoots and roots fresh weights and their lengths in the plant treated with Oxamyl 24% SL (5 ml/l) or the extracts of U. fasciata and Corallina officinalis. These results were closely similar to control. Both of peroxidase and polyphenol enzymes activity for the control plants remained relatively stable, while the activity of the two enzymes in the plant inoculated with the nematode decreased during 2 to 18 day post inoculation (dpi). These activities increased in inoculated plants treated with C. officinalis, C. mediterranea, and U. fasciata extracts and the other plants treated with Oxamyl 24% SL (5 ml/l). The maximum activity of the three enzymes was recorded at 5 dpi after treatment with U. fasciata.

Brown rot or bacterial wilt of potato caused by Ralstonia solanacearum, is an economically important disease. Potato, cv. Nicola, was found to be relatively highly resistant to the infection with R. solanacearum and showed 15.12% wilt disease index, meantime, cv. Kara showed intermediate resistance with 37.40% disease index while, cv. Spunta was susceptible and showed 80.33% disease index. The role of defense-related enzymes in imparting resistance in potato against R. solanacearum was investigated by quantifying enzymes activity and gene expression of three defenserelated enzymes, peroxidase, polyphenol oxidase and catalase. Peroxidase showed maximum activity 0.

Postharvest diseases cause a great reduction in the quantity and quality of fruits yield. Treatment of tomato fruits with salicylic acid (SA) and Hydrogen peroxide (H 2 O 2 ) elicitors enhanced the resistance to fruit rot caused by Alternaria solani. Moreover, the treatment decreased the development of post-harvesting fruit rot disease. The treatment with either SA or H 2 O 2 individually or in combination on tomato shoots (in farm) decreased the diameter of fruit rotted area, decreased the PG activity, significantly increased PAL, PPO, POD enzyme activities and increased PR2 and PR3 genes expression after fruit harvesting. On the other hand, treatment by elicitors after harvesting decreased both diameter of rotten area and decreased PG activity but increased the activity of the PAL, PPO, POD enzymes. Also, the gene expression of PR2 and PR3 genes were high in compared to treatment by elicitors before fruits harvesting. The same observation was obtained by the combination of SA and H 2 O 2, diameter rotten area was decreased and the PG as well. Significant incensement in the activity of enzymes PAL, PPO, POD, this combined with high expression of both PR2 and PR3 genes.

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