Bacterial leaf spot caused by Xanthomonas campestris pv. vesicatoria (Xcv) and bacterial speck caused by Pseudomonas syringae pv. tomato (Pst) were observed on various tomato and pepper plants in Belgium. The presence of Pst and Xcv was confirmed in these diseased plants. Selective media, culture characterization, electron microscopy investigation, physiological and biochemical reaction tests and tobacco hypersensitivity reaction were used for identification of both bacterial diseases of tomato and pepper. Pathogenicity tests, disease index, germination test and bacterial population counts were carried out to evaluate the severity of both bacterial leaf spot and bacterial speck of tomato and pepper.

The response of pepper varieties to Egyptian broomrape and nodding broomrape was characterized in comparison with tomatoes grown in pots and in aqueous solution, according to two criteria: 1. germination of the parasite's seeds in the presence of the host roots; and 2. the number of parasites per host plant. More than 50% of Egyptian broomrape seeds germinated in the presence of all pepper variety roots except the sweet pepper Maor. However, only a few attached and developed. The two paprika varieties Lehava and Shani were hosts to more parasites than the sweet pepper varieties, and showed as many as 15 parasites per host plant. In contrast, tomato roots induced less then 10% seed germination but were highly susceptible to the parasite (30 parasites per host plant). Damage caused to pepper foliage and fruit was not significant, compared to the heavy damage caused to tomato. Pepper roots stimulated germination of 22 to 26% of nodding broomrape seeds but without the formation of parasitic attachments, whereas tomato roots stimulated germination of less than 10% of the seeds but the plants were then heavily damaged by the parasite. Interplanting of tomato with pepper in nutrient solution did not change the amount of Egyptian broomrape parasites on pepper, but a fourfold increase in the number of nodding broomrape was observed on tomato roots, compared to the number of parasites on tomato roots when planted without pepper.

Tomato, bell pepper, celery and citrus were propagated in planting mixes amended with formulations of commercial biocontrol agents. Root colonization by selected biocontrol agents was evaluated for pepper, tomato and citrus, and found to be generally between 76 to 100% in both greenhouse ebb and flow, and beech-produced plants. Only colonization by Glomus intraradices was low, about 8%. All biological control agents, Trichoderma harzianum, Bacillus subtilis, G. intraradices, Gliocladium virens, and Streptomyces griseovirdis reduced crown rot of tomato in the field, with T. harzianum and B. subtilis being the most effective uniformly among four tests. Four biocontrols reduced Phytophthora root rot on citrus in the field, two applied as a drench to soil in pots reduced Thielaviopsis root rot on citrus, and two biocontrol agents in combination reduced celery root rot caused by Pythium and Fusarium spp., however, none improved above-ground plant growth or health of citrus and celery. Pepper crown and root rot caused by P. capsici was reduced by B. subtilis in one of two tests.

Three distinct viruslike agents were isolated from a wild, symptomless Solanum sp. suspected of being a natural reservoir of tomato leaf curl geminivirus. Two of these contained circular DNA genomes of approximately 2.7 kb and were identified as geminiviruses. Restriction analysis and partial sequencing of viral DNA indicated that the two geminiviruses are related to, but distinct from, the Australian strain of tomato leaf curl virus. These viruses were not mechanically transmissible; however, a mechanically transmissible disease agent was also present, which caused stunting of infected tomato plants followed by shoot elongation and hairlessness. Analysis of nucleic acids from sap-inoculated tomato plants revealed the presence of a circular RNA, which was isolated and shown to be the causal agent of the transmissible disease. The complete nucleotide sequence of this 356-nucleotide RNA revealed that it was a sequence variant of potato spindle tuber viroid.

The direct influence of several biowaste composts on diseases caused by Pythium spp. and the rootknot nematode Meloidogyne incognita was investigated on tomato plants (Lycopersicon esculentum Mill.) in a growth chamber experiment. The composts used in this experiment were GFT-compost, groencompost and Humotex. Five different compost samples with two application rates, a normal dose (25 per cent v/v) and a high dose (50 per cent v/v), were used. A soil collected from a tomato greenhouse, heavy infested with Pythium and M. incognita, was used as inoculum. Tomato seeds (cv. Moneymaker) were sown on this soil after adding compost. The following parameters were evaluated: the emergence of tomato, the percentage of plants killed by Pythium, the stem attack by M. incognita (disease-index), the dry matter production of the aerial plant parts, and the total number of rootknots (M. incognita) on the root system. The suppression of the dieback caused by Pythium and the stem attack by M. incognita was very obvious after adding compost to the infested soil, in comparison with peat and no compost addition, where all plants died mainly as a result of the Pythium-dieback. But protection of the plant against M. incognita was of short term, because the high dose of compost could not overcome a certain attack of M. incognita on the root system, due to heavy infestation of the potting mixture with this nematode.

A vesicular-arbuscular mycorrhizal fungus (VAMF), Glomus mosseae, was tested as a biological control agent of bacterial wilt caused by Pseudomonas solanacearum on three varieties of tomato and two varieties of eggplant. Field experiments were conducted in four different sites. A significant increase in survival rate and yield of tomato and eggplant due to mycorrhizal inoculation in an area naturally infested and artificially inoculated with P. solanacearum was observed. The results of the experiments implied that mycorrhizal inoculation not only increase growth and yield of plants but also showed potential in controlling/decreasing bacterial wilt incidence

The rate of evolution of ethylene by tomato plants was rapidly increased by O3 fumigation. The time course of the increase in 1-aminocyclopropane-1-carboxylic acid (ACC) synthase activity was the same as that in the rate of evolution of ethylene, suggesting that ACC synthase activity might be a rate-limiting step in the evolution of ethylene that is caused by O3 fumigation. The rate of the O3-induced evolution of ethylene was increased by the application of ACC to tomato plants, suggesting the involvement of ACC oxidase in the O3-induced evolution of ethylene. Treatment of plants with tiron inhibited the evolution of ethane, but not of ethylene. These results indicated that evolution of ethylene in O3-treated tomato plants might result from enzymatic reactions catalyzed by both ACC synthase and ACC oxidase, but not from stimulation by O3 of the peroxidation of lipids mediated by free radicals. Pretreatment of leaves with aminoethoxyvinylglycine (AVG), an inhibitor of ACC synthase, significantly inhibited the evolution of ethylene that was induced by O3 and concomitantly reduced the extent of O3-induced visible damage to leaves. Treatment with 2,5-norbonadiene, an inhibitor of the action of ethylene, strongly reduced the extent of visible damage caused by O3, even though it did not suppress the evolution of ethylene. These results indicate that ethylene acts on certain metabolic processes to cause visible damage.

A viroid was isolated from symptomless Brunfelsia undulata plants using the bidirectional PAGE method for analysis of small circular RNA molecules. The viroid was transmitted to tomato by mechanical inoculation. Infected tomato plants developed symptoms smiler to those caused by intermediate strains of potato spindle tuber viroid (PSTVd). Cloning and sequencing revealed that the viroid from Brunfelsia undulata is closely related to the Columnea latent viroid (CLVd). Therefore, the new viroid sequence variant has been named CLVd-B. The Brunfelsia viroid CLVd-B consists of 373 nucleotides, 215 G + C, 158 A + U with a GC content of 57.6%. The most stable rod-like secondary structure of this viroid has 80 G:C, 39 A:U and 11 G:U base pairs with a minimum free energy of -157.2 kcal/mol (-657.1 kJ/mol). The sequence similarity of the right terminal domain of CLVd-B and of tomato apical stunt viroid (TASVd) is higher than the sequence similarity of these domains comparing CLVd and TASVd.

Phytotoxicity, uptake, and metabolism of 1,4-dichlorobenzene (1,4-DCB) by carrot (Daucus carota L.), soybean (Glycine max. L.), tomato (Lycopersicon esculentum Mill.), and red goosefoot (Chenopodiun rubrum L.) cell suspension cultures were studied. Sealed glass systems were utilized for the investigation because 1,4-DCB is volatile. The sealed systems effect the growth of plant cells, but do not provide different results when testing xenobiotic uptake and metabolism. 1,4-Dichlorobenzene (40 microgram in 40 ml medium was taken up by carrot (49%), soybean (50%), and red goosefoot (62%) cells. Only the soybean cell cultures provided evidence of the existence of metabolites of this compound, probably conjugates of chlorophenols. Conditions for phytotoxicity tests were modified because the growth of cell cultures was affected when sealed for longer than 2 d. 1,4-Dichlorobenzene is toxic to cell cultures of the three tested plant species (tomato, soybean, and carrot). Concentrations of 0.5 mM caused 50% growth inhibition in carrot and soybean culture. The tomato cultures were more sensitive, with 0.05 mM causing 50% growth inhibition.