Laboratory experiments were carried out under aseptic conditions to study the effect of nitrogen applied as ammonium nitrate at 0, 20,40,60,80 and 100 ppm (wt per vol) in either distilled H2O or modified Hoagland's solution on germination and radicle length of branched broomrape in association with growing seedlings of different crops. As nitrogen rate increased, seed germination and radicle length of branched broomrape decreased linearly in flax, lentil, pepper, tomato, and wheat in modified Hoagland's solution. Similar responses to nitrogen application were found with distilled water. The parasite's seed germination was considerably lower in the media with wheat than with other crops, and lower still in the absence of crop seedings.

Inula graveolens is a poisonous annual plant of Mediterranean origin. The invasive nature of the plant suggests that it may possess phytotoxic activity. The aim of this study was to assess the ability of I. graveolens to inhibit the growth of different plants in Petri dish and to identify the main bioactive compounds. Bio-guided fractionation of the plant extracts led to the isolation of 2,3,11β,13-tetrahydroaromaticin (THA) and ilicic acid. Both compounds showed selective and significant phytotoxic activity at 25 ppm. Root length of barley, oat, millet, tuberous canary grass and lentils were significantly reduced by 25 ppm of THA, while the root of cauliflower, cress and radish were similarly reduced by ilicic acid at 25 ppm. The structure of each compound was elucidated by using NMR and HR-MS. X-ray crystallography of THA is reported for the first time to confirm the relative stereochemistry of the compound.

The search for disease resistance in wild types is continuing, in order to introduce resistant genes from wild relatives. In this study, we found that the wild melon Cucumis prophetarum was comparably more tolerant to salinity, the damping-off disease caused by the fungus Rhizoctonia solani and the root-knot nematode Meloidogyne incognita. The percentage of wild melon survival was 60% compared to that of the cultivated cucumber Cucumis sativus, which was 15%, when irrigated with NaCl at a concentration of 2500 ppm; and 96% for the wild melon compared with 44% for the cultivated cucumber when irrigated with CaSO4.2H2O at a concentration of 1000 ppm. Wild melon plants were more tolerant to R. solani attack, as only 20% of the plants were infested compared with 100% of infestation observed for the cultivated cucumber. The average number of nematode galls was 250 per plant on the cultivated cucumber when compared with 6.3 per plant on the wild species. Wild melon could be a potential source of resistant or tolerant genes that can be transferable to cultivated cucumbers.

Bioactive guided fractionation was carried out to determine the antifungal activity of the stinkwort weed, Inula graveolens, on various phytopathogenic fungi species. Dried shoots were extracted and partitioned in various solvent systems. The aqueous methanol extract (AqMeOH) inhibited the growth of several soil-borne fungi; Alternaria sp., Fusarium spp. and Rhizoctonia sp. in in-vitro plate assay. Fractionation of AqMeOH extract by column chromatography in dichloromethane/AqMeOH yielded twenty-two fractions of which fractions #2, 3 and 4 showed antifungal activity. Further fractionation of the combined fractions #2, 3 and 4 by column chromatography in solvent system benzene/ethyl acetate on fine silica columns, yielded ten sub fractions of which sub fraction #2 has the most antifungal activity on all fungi in the experiment. The fungitoxicity of sub fraction #2 in terms of percentage inhibition of mycelia growth of all tested-fusaria strains after ten days of incubation was higher compared to that obtained by the fungicide hymexazol (Tachigaren ® 70 WP). The AqMeOH extract significantly reduced browning length at the crown area, a fusarium-known symptom in in-vivo experiments. Furthermore, the growth of Fusarium-treated cucumber plants was enhanced by drenching with AqMeOH extract. The activity of the extract was comparable to the activity of the fungicide hymexazol in improving plant health, and surpassed the fungicide activity in preventing the discoloration of the crown vascular tissue of cucumber at comparable concentrations.

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