The effect of dietary cellulose (5 or 15%) and dried powdered tomato pomace (15%) on the development of hypercholesterolemia and colon carcinoma was studied in male Wistar rats. The animals were fed with a diet containing 0.3% of cholesterol and recieved 12 doses of dimethylhydrazine (20 mg/kg) subcutaneously in one-week intervals. Fiber content in tomato peels was 47.2 g/100 g of dry matter, 10.3% of which was in water-soluble form. Tomato pomace in the diet caused a reduction of serum cholesterol level by 30% during 14 weeks after dimethylhydrazine application while the cellulose content in the diet had no significant effect. Liver content of conjugated dienes was reduced by 40% and the activities of superoxide dismutase and glutathione peroxidase in liver increased twofold by tomato pomaces. Compared to the diet containing 5% cellulose, tomato peels diet caused a significant reduction of the average occurrence of pre-neoplastic lesions (aberrant crypt foci) in the colon. Similarly, tomato peels diet caused a reduction of incidence of the dominant type of tumors (tumour foci characterised as highly differentiated adenocarcinoma with the penetration of tumour cells through lamina basalis) by 50% as well as the total volume of tumours. However, the effect for two last mentioned parameters was on the limit of statistical significancy

Tomato (Lycopersicon esculentum) production is handicapped by damage due to pests and pathogens. Farmers' fields in the western highlands of Cameroon were surveyed during 1993 to 1996 to identify biological constraints in production. Diseases and insect pests are the most important biological limitations in tomato production. Late blight caused by Phytophthora infestans and early blight caused by Alternaria solani are the most severe diseases, while the melon fruitfly (Dacus cucurbitae) is the most prevalent insect pest. Yield losses due to pest damage are high and reach 100 % when the crop is not treated in the wet season. Pest-resistant varieties are not available to farmers. Consequently, growers practise intensive pesticidal spray programmes to limit losses caused by pests and diseases. Results indicate the necessity for the adoption of integrated pest management strategies in tomato production in Cameroon.

Tomato (Lycopersicon esculentum) production is handicapped by damage due to pests and pathogens. Farmers' fields in the western highlands of Cameroon were surveyed during 1993 to 1996 to identify biological constraints in production. Diseases and insect pests are the most important biological limitations in tomato production. Late blight caused by Phytophthora infestans and early blight caused by Alternaria solani are the most severe diseases, while the melon fruitfly (Bacus cucurbitae) is the most prevalent insect pest. Yield losses due to pest damage are high and reach 100/ when the crop is not treated in the wet season. Pest-resistant varieties are not available to farmers. Consequently, growers practise intensive pesticidal spray programmes to limit losses caused by pests and diseases. Results indicate the necessity for the adoption of integrated pest management strategies in tomato production in Cameroon.

Plant-mediated interactions (i.e., induced resistance) between plant pathogens and insect herbivores were investigated using several pests of the cultivated tomato, Lycopersicon esculentum. Single leaflets of tomato leaves were injured by allowing a third-instar Helicoverpa zea larva to feed on the leaflets or by inoculating the leaflets with Pseudomonas syringae pv. tomato (the causal agent of bacterial speck in tomato; Pst) or with Phytophthora infestans (the causal agent of late blight). Leaflets on separate plants were sprayed with benzothiadiazole, a chemical inducer of resistance to Pst. The effects of these treatments on the resistance of uninoculated or undamaged leaflets to both Pst and H. zea were then assessed after appropriate periods of time. The levels or activities of several defense-related proteins were determined in parallel. Infection of leaflets by Pst decreased the suitability of uninoculated leaflets of the same leaf for both H. zea and for Pst. Similarly, feeding by H. zea caused leaf-systemic increases in resistance to both H. zea and Pst. Infection of leaflets by P. infestans, in contrast, had no effect on resistance of leaflets to H. zea. Treatment of leaves with benzothiadiazole induced resistance to Pst but improved suitability of leaflets for H. zea. Feeding by H. zea caused the systemic accumulation of proteinase inhibitor mRNA and the systemic induction of polyphenol oxidase activity; in contrast, treatment with benzothiadiazole and inoculation with P. infestans caused the systemic accumulation of pathogenesis-related protein mRNA and the systemic induction of peroxidase activity. Inoculation of leaflets with Pst caused the leaf-systemic accumulation of both pathogenesis-related protein and proteinase inhibitor mRNA and the systemic induction of both peroxidase and polyphenol oxidase activity. These results provide clear evidence for reciprocal induced resistance involving certain pathogens and arthropod herbivores of tomato. In addition, these results provide several insights into the integration and coordination of the induced defenses of tomato against multiple pests and suggest that the expression of resistance against some pests may compromise resistance to others.

The effects of timing and method of application of Penicillium oxalicum on the control of fusarium wilt of tomato were investigated. Application of P. oxalicum to tomato seedlings in seedbeds reduced disease caused by Fusarium oxysporum f.sp. lycopersici in a growth chamber by 45-49% and in glasshouse experiments by 22-69%. Disease suppression was maintained for 60-100 days after inoculation with the pathogen in the glasshouse. No disease reduction was observed in tomato plants where P. oxalicum was applied to seeds. Treatment with P. oxalicum did not affect the population of F. oxysporum f.sp. lycopersici in the rhizosphere.

The effect of saprobic fungi inhabiting the tomato phylloplane on the expression of tomato early blight (caused by Alternaria solani) was evaluated. Artifical inoculation with the pathogen and the antagonists was carried out in a commercial greenhouse on four-month-old tomato plants (cv. Parador, Asgrow Seeds, Co.). Inoculation with the antagonist was made an hour before inoculation with the pathogen. Inoculum of saprobic fungi was produced on potato-dextrose agar (PDA). The concentration of the microorganism propagules was diluted to 100000000 c.f.u./ml. Alternaria solani inoculum was obtained on cornmeal agar and the concentration used for the inoculation was 1000000 c.f.u./ml.

Tomato high pigment (hp) mutants are characterized by their exaggerated photoresponsiveness. Light-grown hp mutants display elevated levels of anthocyanins, are shorter and darker than wild-type plants, and have dark green immature fruits due to the overproduction of chlorophyll pigments. It has been proposed that HP genes encode negative regulators of phytochrome signal transduction. We have cloned the HP-2 gene and found that it encodes the tomato homolog of the nuclear protein DEETIOLATED1 (DET1) from Arabidopsis. Mutations in DET1 are known to result in constitutive deetiolation in darkness. In contrast to det1 mutants, tomato hp-2 mutants do not display any visible phenotypes in the dark but only very weak phenotypes, such as partial chloroplast development. Furthermore, whereas det1 mutations are epistatic to mutations in phytochrome genes, analysis of similar double mutants in tomato showed that manifestation of the phenotype of the hp-2 mutant is strictly dependent upon the presence of active phytochrome. Because only one DET1 gene is likely to be present in each of the two species, our data suggest that the phytochrome signaling pathways in which the corresponding proteins function are regulated differently in Arabidopsis and tomato.

In September 1997, leaf curling and yellowing were observed on tomato plants on a farm on the south coast of La Reunion, a French island in the Mascarenes archipelago. Based on the similarities of the symptoms caused by geminiviruses on tomato, the diagnosis was oriented towards the detection of a geminivirus. Using degenerate primers designed to amplify a region of the A component of most of the begomoviruses (formerly sub-group 111 geminiviruses), a 500 base pair PCR product was obtained with a diseased plant, but not with a healthy looking one. Based on sequence similarities, it was shown that the detected geminivirus was an isolate of the tomato yellow leaf curl virus from Israel (TYLCV-IL). (Résumé d'auteur)

To test the hypothesis that host-related differences in the genotypic composition of populations of the late blight pathogen Phytophthora infestans can be explained by differential pathogenicity, the aggressiveness of isolates of the pathogen collected in France from potato and tomato was measured on detached leaflets of potato (cv. Bintje) and tomato (cv. Marmande). A preliminary trial with four isolates (two each from potato and tomato) showed that lesion appearance and development were similar for each isolate in detached leaflets and in whole plant tests in growth cabinets. Isolates collected from tomato were more pathogenic to tomato than isolates collected from potato. This was particularly the case for isolates belonging to the A2 mating type. Isolates originating from potato had a higher infection efficiency and a higher sporulation capacity on this host, but they induced lesions that generally spread more slowly than those caused by isolates from tomato. Extensive variation for components of aggressiveness on potato, and to a lesser extent on tomato, was observed in collections of isolates from each of the two hosts. Competition experiments between one potato isolate and one tomato isolate in field plots of the susceptible potato cv. Bintje clearly demonstrated the higher competitive fitness of the potato isolate on its host of origin. Therefore, differential pathogenicity to potato and tomato certainly contributes to the differentiation between P. infestans populations present on potato and tomato in France; however, additional factors, possibly related to survival ability or random genetic drift, are probably also involved and may explain the persistence of weakly pathogenic isolates in these populations.

The experiments were carried out in 1997-1998 in greenhouses with cucumber, tomato and pepper cultivars to establish the preference of the pest to some of them, judging on the degree of the damages caused. Liriomyza huidobrensis Blanchard showed preference to cucumber, followed by tomato. Pepper was the least preferred. From 13 tomato cultivars the most heavily attacked were Baldo and Ruen, the least preferred - Kom, Rila and Balkan. The degree of damage varied from 23,05 to 31,46% mined leaves per plant. From 6 cucumber cultivars the least preferred was cv. Aricya, and the most attractive for the leafmining flies were the cultivars Piralis, Kalunga, Sandra and Fitness. The degree of damage is higher, compared to that of tomatoes, and varies from 67,05 to 85,03% mined leaves per plant. The pepper cultivar Hebar is less preferred, compared to cv. Albena. The pepper was the most attractive for the females for making fedding punctures with 0,76 per cm2 leaf surface, while for cucumber the value was 0,22 (cv. Sandra) to 0,55 (cv. Guergana), and for tomato - 0,08 punctures/cm2.