Streptomyces sp., a cause of fistulous withers in donkeys

Four of 10 donkeys, which showed lesions simulating fistulous withers, were examined clinically with the aim to cultivate and identify the causal agent. Aspiated purulent materials were subjected to bacteriological examination. The causal organisms were recovered in Tryptic Soya agar medium when incubated aerobically at 37 degrees C for up to 5 days. These organisms were found to be actinomycetes-like, Gam positive with stable branching filaments and to form heavy aerial hyphae on colony surface. The isolated organisms ere tentatively identified as Streptomyces sp. on the basis of morphological and cultural characteristics. The initial sequences analysis of the 16S rDNA gene conformed that one of the isolates (SD551) falls within the phylogenetic clade, which encompasses the genus Streptomyces. Studies are underway to further describe the disease and its causal agent. The report represents a good evidence to incriminate Streptomyces in the aetiology of the fistulous withers.     

Premières observations de Verticillium dahliae sur olivier en Tunisie

Au cours des prospections effectuées dans les oliveraies de la délégation de Mahres (région de Sfax) située au centre-est de la Tunisie, 12 cas de dépérissement d'oliviers âgés, du cv. 'Chemlali' ont été observés dans deux parcelles voisines. Dans ces deux vergers, les oliviers malades sont répartis en foyers. Les investigations au champ et au laboratoire ont permis de mettre en évidence la présence du champignon Verticillium dahliae , qui est ainsi signalé pour la première fois en Tunisie sur olivier.     

Phenotypic responses of the wild wheat relative Aegilops geniculata Roth and wheat (Triticum durum Desf.) to experimentally imposed salt stress

In order to study the salt effect on the wild wheat and durum wheat, three accessions of Aegilops geniculata L. from Ain zana, Zaghouan, and Sbitla and one variety of wheat (Triticum durum L.) have been grown in the INRAT green house and treated with different salt concentrations. The morphological, phenological and yield characters have been measured for each plant and analyzed using SAS software. This study has shown a high degree of variation of these characters mainly related to geographical origin. It was observed also that Sbitla accession was less affected by the imposed salt stress than all the others while Ain zana was the most affected one.     

Codend selectivity for jack mackerel and whitefin jack and unequal split parameter estimates observed in trouser trawl experiments

Codend selectivity for the jack mackerel Trachurus japonicus and the whitefin jack Kaiwarinus equula were evaluated based on data from trouser trawl experiments carried out in the East China Sea, using a test codend of 60 mm diamond mesh and a control codend made of minnow net with a square mesh of 9 mm bar length. Between-haul variations in parameters and the mean selection curves were tested with the catch data in the SELECT approach, and then the model of between-haul variation in the split parameter with the mean selection curve was chosen as the best fit using Akaike’s information criterion model selection. The 50% retention lengths and the selection ranges were 11.4 and 3.36 cm for jack mackerel and 8.83 and 0.93 cm for whitefin jack, respectively. The selection curve for whitefin jack was sharp, whereas that for jack mackerel was relatively wide. As the estimated split parameters indicated, about 80% of the whitefin jack entered the control codend, but 85 and 90% of the jack mackerel entered the control codend in the second and third hauls, respectively. The inequality in the split parameter is discussed from the viewpoint of the animal’s swimming behavior and water movement based on underwater video observations.     

Effects of Bacillus subtilis on the water quality,stress tolerance,digestive enzymes,growth performance,immune gene expression,and disease resistance of white shrimp (Litopenaeus vannamei) during the early hatchery period

Aquaculture International - In the present study, the white shrimp, Litopenaeus vannamei, was supplemented with the probiotic Bacillus subtilis IS02 in order to improve the larval survival rate....     

Leak syndrome of potato in Tunisia caused byPythium aphanidermatum andPythium ultimum

Summary TwoPythium spp. were isolated from diseased tubers exhibiting rots at harvest, in summer stores and also in refrigerated storage. Symptoms shared features described for both pink rot caused byPhytophthora erythroseptica and leak caused byPythium spp. The causal agents were identified asPythium aphanidermatum andP. ultimum by morphological and physiological observations and by fingerprinting using oomycete specific primers to amplify the internal transcribed spacer (ITS1) within ribosomal DNAs. The optimum temperatures for infection were 30°C forP. aphanidermatum and 25°C forP. ultimum, corresponding to the optimum temperatures for growth in vitro. The optimum concentration for infection of tubers inoculated by dipping in a suspension of oospores or hyphal swellings after wounding was found to be 10³ reproductive organs/ml, whereas the infection threshold was 10 reproductive organs/ml.     

Effects of soil solarization on soil-borne populations ofPythium aphanidermatum andFusarium solani and on the potato crop in Tunisia

Summary Soil solarization by mulching with polyethylene for 60 days during summer in Tunisia, was effective in reducing dramatically to a depth of 30 cm inoculum levels ofFusarium solani (Fs) from 3,000 to 450 propagules gram⁻¹ of dry soil. Population densities ofPythium aphanidermatum (Pa) were reduced from 1,700 and 3,000 to 0.5 and 1 propagule gram⁻¹ of dry soil in the top 15 cm and at 1–30 cm depth, respectively. After a subsequent autumn potato crop, populations ofPa remained very low in the previously solarized soil whereas propagule density in non-solarized soils was similar to the initial density. Also, inoculum level ofFs increased by 40% in nonsolarized soils while it remained unchanged in solarized soils, suggesting microbial processes that prevented soil reinfestation. All the annual weeds were eradicated by solar heating but not the perennial weedConvolvulus arvensis. Potato plant growth and yields were improved in solarized plots.     

Assessing potato cultivars in Tunisia for susceptibility to leak caused byPythium aphanidermatum

Summary The susceptibility of 21 potato cultivars to leak (watery wound rot) caused byPythium aphanidermatum was compared. Whole tubers were inoculated after wounding by dipping into a water suspension of 10³ oospores/ml and incubated for 3 days at 25°C. The mean penetration of tissue calculated from the recording of lesion width and depth and the qualitative assessment of rot extension were highly correlated. For 10 of 12 cultivars tested at least twice, consistent reactions were obtained: cvs Korrigane. Superstar, Safrane and Yesmina were moderately susceptible, whereas Atlas, Diamant, Mondial, Obélix, Spunta and Timate were susceptible to highly susceptible. Tubers originated from two locations and/or two cropping seasons: thus, the performance of these cultivars under different production conditions reveals a satisfactory level of agreement with the test. Moreover, ratings assigned are supported by field or store observations.