Volume 3 Number SI1 2009
Tunisian Plant Science and Biotechnology I

Guest Editor

Mejda Daami-Remadi

Centre Régional des Recherches en Horticulture et Agriculture Biologique, Chott-Mariem, Tunisia

www.iresa.agrinet.tn/fr/instit/p_crrhab.htm

CONTENTS AND ABSTRACTS

Riadh Ilahy, Chafik Hdider, Imen Tlili (Tunisia) Bioactive Compounds and Antioxidant Activity of Tomato High Lycopene Content Advanced Breeding Lines (pp 1-6)

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Original Research Paper: In Tunisia, tomato (Lycopersicon esculentum Mill.) is the main ‘vegetable’ grown and consumed all year round and is therefore of strategic importance. Tomato fruits are becoming then an important source of natural antioxidants primarily lycopene, phenolics and vitamin C, which are involved in inhibiting reactive oxygen species responsible for many cancer and cardiovascular diseases. Breeding for high nutritional tomato value is becoming an increasingly important aim. In this context, tomato high lycopene content advanced breeding lines (HLT-F51 and HLT-F52) were evaluated for their total carotenoid, lycopene, total phenolics, flavonoids, ascorbic acid, dehydroascorbic acid as well as their hydrophilic and lipophilic antioxidant activities, compared to the variety Rio Grande commonly grown in Tunisia. All tested high lycopene content varieties showed generally satisfying agronomic characteristics. The total carotenoid, lycopene, total phenolics, flavonoids, dehydroascorbic acid, total vitamin C and hydrophilic and lipophilic antioxidant activities in tomato fruit varied significantly between the studied varieties. Compared to the control, the selected line HLT-F51 showed 2.65-, 2.62 and 3.57-fold higher total carotenoid, lycopene and flavonoids, respectively. Also, HLT-F51 showed 2.09 and 2.24-fold higher hydrophilic and lipophilic antioxidant activities respectively. HLT-F52 exhibited particularly higher dehydroascorbic acid and total vitamin C contents compared to the control variety Rio Grande. These results emphasize the promising use of such advanced breeding lines for healthy quality products.

Imen Tlili, Chafik Hdider, Riadh Ilahy, Hager Jebari (Tunisia) Assessing Agronomic Characteristics and Physicochemical Properties of Selected Watermelon Varieties Grown in Tunisia (pp 7-11)

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Original Research Paper: Watermelon (Citrullus lanatus (Thunb.) Mansfeld) is a popular vegetable. Interest in assessing agronomic and bioactive compounds with antioxidant capacity and potential health benefits in watermelon is increasing. Besides some agronomic characteristics, the variability of lycopene and total phenolic contents of six watermelon varieties (four commercial cultivars ‘Aramis’, ‘Crimson Sweet’, ‘Dumara’, ‘Giza’, and two new selections P503 and P403 developed by the National Agricultural Research Institute of Tunisia) as influenced by sampling area was determined. ‘Giza’ and P503 were characterized by small fruits with a thin rind and a relatively high amount and large seeds. Significant differences were found in lycopene and phenolic contents between watermelon varieties. Lycopene content in P503 and ‘Giza’ was more than 2-fold higher than that in ‘Dumara’ and P403. The highest phenolic value (90.28 mg GAE kg^-1 FW) was shown by ‘Dumara’. The lycopene and total phenolic contents varied significantly between studied sampling areas but not in all varieties. Generally, highest values for lycopene and total phenolics were obtained for heart and stem end areas. For all studied watermelon varieties, lycopene was best correlated with rind thickness and 100-seeds weight. This study demonstrates that the amount of lycopene and total phenolics were both influenced by genotype and sampling area, emphasizing the need to adopt standardized and documented sampling methods when assessing quality attributes, and to evaluate watermelon biodiversity in order to improve its nutritional value.

Mahmoud M’Hamdi, Hela Beji (Tunisia), Lassaad Belbahri (Switzerland), Taoufik Bettaieb, Karima Kouki, Youssef Harbaoui (Tunisia) Hydrogen Peroxide and a Catalase, Physiological Regulators of Potato (Solanum tuberosum L.) Tuber Dormancy (pp 12-15)

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Original Research Paper: The involvement of hydrogen peroxide (H₂O₂) metabolism and catalase activity in dormancy release and sprouting of potato (Solanum tuberosum L.) tubers has been investigated in nine cultivars with a contrasting dormancy length. Phenotypic characterisation of tubers dormancy was established for all cultivars by following sprouting kenetics (percent of sprouted tubers following time during storage period). Catalase (CAT) activity and H₂O₂ content were measured during two important tuber physiological stages: dormancy and sprouting. Our results revealed three groups of cultivars according to the length of dormancy: ‘Arinda’, ‘Santana’, and ‘Safrane’, with short dormancy (7-8 weeks), ‘Mondial’, ‘Atlas’, and ‘Liseta’, with long dormancy (15-16 weeks) and ‘Spunta’, ‘Tango’, and ‘Nicola’, with intermediate dormancy (12-13 weeks). 80% of cultivars with short dormancy sprouted between the 5^th and 6^th week after harvest, between the 9^th and 10^th week for the second group with intermediate dormancy and between the 12^th and 13^th week for the cultivars with long dormancy. Biochemical characterisation showed CAT activity and low H₂O₂ content during the dormancy stage for all cultivars. CAT activity varied between 30 and 18.57 µmol H₂O₂ min^-1 mg^-1 of protein for ‘Atlas and ‘Nicola, respectively. For H₂O₂, the values ranged between 5.1 and 16.92 mmol (gFW)^-1 in ‘Tango’, and ‘Liseta’, respectively. Sprouting was associated with a significant increase in H₂O₂ content (85.35 in ‘Arinda’, and 172.5 mmol g^-1 FW^{-1 in} ‘Santana’) and a decrease of CAT activity (5.09 in Tango and 13.15 µmol H₂O₂ min^-1 mg^-1 of protein in ‘Satana’.

Amel Kerkeni, Neji Tarchoun, Mohamed Ben Khedher (Tunisia) Animal Manure Composts as Potting Media for Production of Pepper (Capsicum annuum) Transplants (pp 16-19)

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Short Communication: Different types of growing media were evaluated in nursery-produced peppers plants (Capsicum annuum L. cv. ‘Rouge Long’). Five local composts (C1, C2, C3, C4 and C5), based on animal-manures (chicken, sheep, cattle and horse manure), used alone or in mixture with commercial peat (PT) were tested in this study. A control of 100% PT was compared to PT: compost mixtures at 50: 50 (v/v) and to 100% compost. Various seedling parameters were measured in order to assess the quality of the nursery-produced plants. The carbon: nitrogen ratio (C/N) of the medium decreased considerably as the level of compost increased, while pH increased. Electrical conductivity of all media was high (>3 dS.m^-1). Despite the quality of the composts used (pH and salinity), growth in media consisting of composts, used at 100% or in a 1: 1 mixture with PT, was more acceptable (stem length and plant dry matter) than growth in peat alone. Although the five composts had different composition, they performed relatively similarly as potting media. No significant difference was observed between seedlings grown in 100% compost and those grown in 50% compost: 50% peat. 100% mature animal-manure composts were horticulturally acceptable as alternatives to 100% peat for pepper transplant production.

Nouha Hibar-Beji, Mejda Daami-Remadi, Khaled Hibar, Mohamed El Mahjoub (Tunisia) Effect of Substrate Culture on the Development of Fusarium Crown and Root Rot of Tomato (pp 20-23)

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Original Research Paper: Fusarium crown and root rot of tomato is a new damaging disease of tomato plants in Tunisia. A study of the effect of culture substrate on the development of this disease revealed that Fusarium oxysporum f. sp. radicis-lycopersici (Forl) is highly virulent when tomato plants are transplanted to sand, topsoil or perlite. Adding compost to these substrates significantly reduced the expression of this pathogen. Indeed, disease incidence measured in a mixture of perlite and compost was only about 6.6%; however this value exceeded 43% when tomato plants were transplanted only to perlite. These results suggest the suppressive effect of compost on the development of Forl and on soil-borne pathogens in general.

Hayfa Jabnoun-Khiareddine, Mejda Daami-Remadi (Tunisia), Dez Barbara (UK), Mohamed El Mahjoub (Tunisia) First Report of Verticillium tricorpus from Potato Tubers and Plants in North Africa (pp 24-25)

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Research Note: In field surveys in the potato growing areas in Tunisia, a dry rot of potato tubers cv. ‘Spunta’ was observed at harvest but at a low frequency (2%) compared to the other typical dry rots caused by Fusarium spp. Based on macroscopic and microscopic characters of the collected isolates, the fungus was identified as V. tricorpus. This funguswas also isolated from many wilted potato plants, alone or together with V. dahliae. Pathogenicity tests were performed on wounded and unwounded potato cv. ‘Spunta’ tubers and on plants. A dry rot was observed on wounded inoculated tubers and moderate but typical Verticillium wilt symptoms were occasioned on inoculated plants within 30 days of incubation. Some of the collected isolates grown on PDA amended with benomyl at different rates (0, 0.1, 1, 10 and 100 mg/l), 10 were resistant to benomyl as their minimum inhibitory concentration was greater than 10 mg/l.

Hayfa Jabnoun-Khiareddine, Mejda Daami-Remadi, Fakher Ayed, Mohamed El Mahjoub (Tunisia) Biological Control of Tomato Verticillium Wilt by Using Indigenous Trichoderma spp. (pp 26-36)

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Original Research Paper: Three endogenous Trichoderma species were tested in vitro, in vivo and in situ for their antagonistic activity against Verticillium spp. causing tomato vascular wilt in Tunisia. Trichoderma harzianum, T. viride and T. virens isolates reduced the radial growth of V. dahliae, V. albo-atrum and V. tricorpus in comparison to the untreated controls. Antagonistic potential of Trichoderma spp. against tested wilt agents showed intra- and inter-specific variations. Additionally to the sclerotinization inhibitory activity and to the reduced abundance of resting structures of Verticillium spp. observed, comparatively to untreated controls, Trichoderma spp. isolates caused profound alterations of Verticillium spp. mycelium at the confrontation zone. The germination of V. dahliae microsclerotia, exposed for 30 min to liquid cultures of antagonists tested and incubated at 20°C, was completely suppressed compared to the control microsclerotia treated with sterile distilled water. Furthermore, germinating microsclerotia dual cultured with Trichoderma spp. became unable to germinate and mature microsclerotia progressively lost their typical dark colour. All tomato cv. ‘Ventura’ plants, when treated at planting with a Trichoderma spp. spore suspension and inoculated with V. dahliae, showed after 60 days of culture under growth chamber conditions, a reduced severity of Verticillium wilt in comparison to inoculated and untreated control plants. In addition, plants treated with Trichoderma spp. showed increased height and root and stem fresh weights in comparison to the inoculated and untreated control. The discoloration index, noted on tomato plants treated at planting by T. harzianum, T. viride and T. virens and grown under greenhouse conditions, was significantly reduced compared to the untreated control. Plants treated with Trichoderma spp. showed, after 90 days of culture, an increase of more than 50% of their roots and stem fresh weights in comparison to the untreated control.

Ziad Borgi, Khaled Hibar, Naima Boughalleb, Hajer Jabari (Tunisia) Evaluation of Four Local Colocynth Accessions and Four Hybrids, Used as Watermelon Rootstocks, for Resistance to Fusarium Wilt and Fusarium Crown and Root Rot (pp 37-40)

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Original Research Paper: Fusarium wilt and Fusarium crown and root rot, caused by Fusarium oxysporum f. sp. niveum and F. solani f. sp. Cucurbitae, respectively are damaging diseases of watermelon in Tunisia. While causing heavy losses to watermelon production, no or some effective disease control methods are available. In Tunisia, there are no approved fungicides to control these diseases. The use of tolerant or resistant rootstocks seems to be the most effective measure. Using local colocynth accessions seems to be a reliable solution for controlling Fusarium wilt and Fusarium crown and root rot. Indeed, the percent of diseased plants did not exceed 8.6%. Used as parental accessions and hybridized with Citrullus lanatus var. citroides, they generated resistant hybrids whose percentage of diseased plants was no more than 8.3%. These results suggest that colocynth accessions as well as the generated hybrids seem to be potential watermelon rootstock that can be used in Tunisian orchards where Fusarium species cause problems.

Hechmi Mehri, Raoudha Mehri-Kamoun, Khaled Hibar (Tunisia) In Vitro Evaluation of Resistance of Pyrus syriaca, a Pear-tree Rootstock, to Phytophthora Crown Rot (pp 41-43)

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Research Note: Phytophthora crown rot, caused by Phytophthora cactorum, is a damaging disease of apple, peach and plum in Tunisia. While causing heavy losses to fruit production, no or some effective disease control methods are available. In Tunisia, there are no approved fungicides to control P. cactorum. The use of tolerant or resistant rootstocks seems to be the most effective measure for controlling Phytophthora crown rot. Pyrus syriaca, a pear-tree rootstock, was tested for resistance to P. cactorum, demonstrating high resistance to this pathogen. Indeed, on excised twigs, the necrotic length ranged between 1.22 and 0.67 mm. However, this value varied between 12 and 15 mm for Myrandier 617, known to be sensitive to P. cactorum. In in vitro experiments, the percentage of necrotic plants varied between 1.8 and 1.9% for the rootstock P. syriaca. These values were almost equal to those obtained with GF 667. However the percentage of necrosis in vitro plants obtained with Myrandier 617 varied from 86.2 to 95.2%. These results suggest that P. syriaca seems to be a potential pear-tree rootstock that can be used in Tunisian orchards where P. cactorum causes problems.

Hechmi Mehri, Raoudha Mehri-Kamoun, Khaled Hibar (Tunisia) Response of ‘Ousleti’ Olive Pollen to Pseudomonas syringae pv. savastanoi Culture Filtrate (pp 44-48)

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Original Research Paper: Olive knot is the only bacterial disease of the olive tree, caused by Pseudomonas syringae pv. savastanoi L. The most effective measure for controlling this bacterial disease is the use of resistant cultivars because chemical control is not effective. ‘Ousleti’, an important local olive cultivar in Tunisia, is reported to be resistant to this bacterial disease although there is no scientific study to prove this. In this preliminary study, the effect of a toxic culture filtrate of P. savastanoi on pollen germination and pollen tube growth was evaluated in vitro on two Tunisian olive cultivars; one tolerant ‘Ousleti’ and one susceptible ‘Chemlali’. The variety x treatment interaction was significant indicating that cultivars differed in their response to the treatment. Cultivar differences in the reaction of olive pollen to bacterial filtrate were noted. The addition of P. savastanoi culture filtrate to the germination medium had no significant effect on the percentage of pollen germination and the tube length in the tolerant olive cultivar ‘Ousleti’ in comparison to its control but they were highly reduced in the susceptible one, ‘Chemlali’. In addition to inhibiting pollen germination and tube elongation in ‘Chemlali’, culture filtrate applied to culture medium also influenced tube morphology. Several abnormalities in pollen tube growth were observed when culture filtrate was added to germination medium of ‘Chemlali’ pollen. These results suggest that this tested method, based on pollen response, enabled rapid and effective evaluation of P. savastanoi on olive pollen grains then on olive resistance. Also, the percentage of pollen germination and tube growth in the presence of culture filtrate medium might be correlated with the plant’s response to the pathogen.

Brahim Chermiti, Khaled Abbes, Mariem Aoun, Soukaina Ben Othmane, Mohamed Ouhibi, Wafa Gamoon, Sonia Kacem (Tunisia) First Estimate of the Damage of Tuta absoluta (Povolny) (Lepidoptera: Gelechiidae) and Evaluation of the Efficiency of Sex Pheromone Traps in Greenhouses of Tomato Crops in the Bekalta region, Tunisia (pp 49-52)

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Original Research Paper: Monitoring Tuta absoluta with pheromone traps and weekly sampling in the Bekalta cropping area showed that the population dynamics of the insect on young tomato leaves can be separated into three phases: low infestation initially (from 25^th March to 6^th May, 2009), followed by a growing population with a dominance of eggs and of first instar larvae (from 6^th May to 27^th May, 2009), then a decline phase accompanied by progressive drying of tomato plants (from 27^th May to 3^rd June, 2009). Mass trapping in the experimental greenhouses was not efficient compared to the control. The study revealed that fruit losses do not depend on the presence or absence of a sex pheromone trap because all greenhouses in this biotope were not isolated from the external environment with an insect-proof which can prevent the entry of T. absoluta adults. Losses in 9 representative greenhouses were between 11.08 and 43.33% with an average deficit of 809 kg for an average total production of 4156 kg, corresponding to a 20% loss.

Mohamed Elimem, Brahim Chermiti (Tunisia) Population Dynamics of Frankliniella occidentalis Pergande (1895) (Thysanoptera: Thripidae) and Evaluation of its Different Ecotypes and their Evolution in a Rose (Rosa hybrida) Greenhouse in the Sahline Region, Tunisia (pp 53-62)

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Original Research Paper: Monitoring population dynamics of Frankliniella occidentalis Pergand (1895) (Thysanoptera; Thripidae) employing blue sticky traps and the weekly collection of flowers allowed the determination of the critical periods of insect population increase in Tunisia, namely spring and early summer. Indeed, the maximum F. occidentalis population was recorded during June, while the lowest number of thrips was observed during winter. On the other hand, the observations revealed that the number of males decreased gradually compared to females mainly in summer with a proportional decrease in the sex ratio. On the other hand, a study of the occurrence of natural enemies associated with Californian thrips led to the identification of a predatory bug Orius insidiosus Say (1832) (Heteroptera: Anthocorridae) which was frequently observed in the sampled flowers. This predator declined F. occidentalis population 5 weeks after its natural introduction and installation into the rose crop greenhouse. Moreover, regular prospecting realized on 2007 in rose crop greenhouses in the Sahline region in Tunisia permitted to distinguish different ecotypes of western flower thrips Frankliniella occidentalis Pergand (1895) (Thysanoptera, Thripidae). Indeed, based on their color, three ecotypes were found: dark, pale yellow and intermediate color. The temporal evolution of these three ecotypes was studied depending on environmental conditions. In fact, the dark ecotype was shown to be mostly abundant during winter and spring and to decrease in summer but did not disappear. However, the pale yellow ecotype was completely absent during the cold season, appeared in spring and summer and dominated the western flower thrips population. The ecotype of intermediate color was present throughout the year without showing too much variation.

Abdessatar Omezine, Fethia Harzallah-Skhiri (Tunisia) Biological Behavior of Cyperus rotundus in Relation to Agro-Ecological Conditions and Imposed Human Factors (pp 63-69)

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Original Research Paper: Field and laboratory experiments were conducted to study the biological behavior of C. rotundus over a two-year period (2006-2007). Spatial distribution, viability and tuber formation were investigated. The effect of propagule size, storage conditions, soil moisture and multiple tubers in rhizome chains on tuber sprouting of C. rotundus were determined. C. rotundus forms a large number of tubers per plant, 46% of which are able to sprout. However, 54% undergo dormancy. Distribution of tubers in the soil profile is most abundant in the 0-12 cm layer, accounting for 78.6% of all tubers but the depth can attain 40 cm and is expected to be deeper. In C. rotundus, the apical bud inhibits sprouting in other buds on the same tuber, and the top tuber exerts a similar dominance over the lower tubers in the system. The viability of tubers decreases in an inverse linear manner over an increasing range of burial depth. C. rotundus tubers are very sensible to desiccation. Moisture levels in the soil must increase to a critical level before sprouting occurs, but excess soil moisture deters sprouting. Tuber emergence and emergence time depend upon tuber size and burial depth. Systems to manipulate sprouting may provide new strategies for C. rotundus management.