Mohamed El Gazzah

Genetic diversity of faba bean ( Vicia faba L.) populations revealed by sequence specific amplified polymorphism (SSAP) markers

This study used sequence specifc amplifcation polymorphism (SSAP) markers to investigate the genetic diversity and population genetic structure of nine Tunisian Vicia faba populations belonging to the minor and major faba bean’s sub-species. Three primers were used (PDR1, Tps19 and Tvf4 ) in this study. These primers gave good SSAP marker profiles, high number of bands obtained per gel and a high percentage of polymorphic bands as confirmed in a previous study. Indeed, these primers provided a total of 173 amplified bands, with 123 of them being polymorphic. Shannon indexes ranges from 0.166 to 0.248 with an average of 0.207. The genetic diversity within population of 0.743 was clearly higher than that of among population genetic diversity (Dst = 0.138), indicating an out-crossing predominance in the studied populations. The Dst value showed that 15.6% of the total genetic variation resided among populations, a little lower than that of out-crossing species. The dendrogram grouping the populations by unweighted pair-group method with arithmetic averages (UPGMA) method revealed three main clusters. The local major faba bean ‘Batata’ was the most divergent population and was separated from other population.

Relationship between epistasis and aggressiveness in resistance of pepper (Capsicum annuum L.) to Phytophthora nicotianae

This study evaluated the types of gene action governing the inheritance of resistance to Phytophthora nicotianae necrosis in populations derived from two crosses involving two susceptible (Beldi and Nabeul II) and one resistant (CM334) cultivars of pepper (Capsicum annuum L.). Populations, composed of Pr, Ps, F1 , F 2 , BC 1 Pr, and BC 1 Ps generations, were inoculated with six P. nicotianae isolates. Generation means analysis indicated that an additive-dominance model was appropriate for P. nicotianae isolates Pn Ko1 , Pn Ko2 and Pn Kr1 , which showed low aggressiveness in the two crosses. For the more aggressive isolates Pn Bz1 , Pn Bz2 and Pn Kr2 , epistasis was an integral component of resistance in the two crosses. The presence of epistasis in the resistance of pepper to P. nicotianae was dependent on the level of aggressiveness of the isolates. Selection in pepper with less aggressive isolates was efficient, but not with more aggressive isolates; on the other hand, selection with more aggressive isolates was more stable. The minimum number of genes controlling resistance was estimated at up to 2.71. In the majority of cases, the additive variance was significant and greater than the environmental and dominance variance.

Epistasis and genotype-by-environment interaction of grain protein content in durum wheat

Parental, F1 , F 2 , BC 1 and BC 2 generations of four crosses involving four cultivars of durum wheat (Triticum durum Desf.) were evaluated at two sites in Tunisia. A three-parameter model was found inadequate for all cases except crosses Chili x Cocorit 71 at site Sidi Thabet and Inrat 69 x Karim at both sites. In most cases a digenic epistatic model was sufficient to explain variation in generation means. Dominance effects (h) and additive x additive epistasis (i) (when significant) were more important than additive (d) effects and other epistatic components. Considering the genotype-by-environment interaction, the non-interactive model (m, d, h, e) was found adequate. Additive variance was higher than environmental variance in three crosses at both sites. The estimated values of narrow-sense heritability were dependent upon the cross and the sites and were 0%-85%. The results indicate that appropriate choice of environment and selection in later generations would increase grain protein content in durum wheat.

Rhamnus lycioides in Tunisia is a new aecial host of oat crown rust

Puccinia coronata was not previously described on Rhamnus spp. in Tunisia. Three sites in the northwest of Tunisia, where Rhamnus is reported to be abundant, were surveyed for the presence of pycnia and aecia of oat crown rust caused by Puccinia coronata f. sp. avenae. Two Rhamnus species (R. lycioides and R. alaternus) were encountered in the sites. Pycnia with viable pycniospores and aecia with viable aeciospores were found on R. lycioides. However, no characteristic structures of crown rust were found on R. alaternus. Aeciospores collected from leaves of R. lycioides were used to inoculate oat plants usually susceptible to oat crown rust. Typical uredinia containing oat crown rust urediniospores appeared on the leaves of these plants. Moreover, the sixteen Pc-gene differential oat lines, used by oat researchers to study the virulence pattern in oat crown rust populations, were artificially inoculated with aeciospores from R. lycioides. These inoculated lines showed resistance/susceptibility similar to the registered resistance level of these lines to crown rust under field conditions in Tunisia. These results indicate that R. lycioides, a common and endemic part of the vegetation in the northwest of Tunisia, is a new aecial host of oat crown rust. The aeciospores produced on this forest plant could constitute the source of the virulence diversity already detected via the Pc-gene line trials.

Karyological and genome size insights into cardoon (Cynara cardunculus L., Asteraceae) in Tunisia

This study contributes the first genome size data for wild populations of Cynara cardunculus, the presumed progenitor of artichoke and cultivated cardoon. C-values estimated by flow cytometry are 2C = 1.98–2.14(3.03) pg for wild cardoon (10 populations), 2C = 2.10–2.11 pg for cultivated cardoon (two accessions) and 2C = 2.05 pg for artichoke (one accession). Chromosome counting (carried out for all material except the artichoke) establishes diploidy in all accessions. In order to provide a phylogenetic framework for Tunisian populations, internal transcribed spacer (ITS) region was sequenced and analysed together with previously published Cynara sequences. The wild and crop cardoons present similar karyological features and genome sizes despite strong morphological differentiation, with the single exception of a Tunisian population (from Tajerouine), which exhibits a 42–53% higher genome size. Along with Sicilian individuals, Tunisian wild C. cardunculus appear genetically closer to artichoke and cardoon than to studied wild relatives from the remaining distribution. This highlights the crucial importance of taking into consideration the North African territory in deciphering the history of C. cardunculus crop domestication.

Relationship between leaf stages and epistasis for resistance to Stagonospora nodorum in durum wheat

Ten varieties and eight generations (2F1, 2F2, 2B1 and 2B2) of durum wheat derived from two crosses were evaluated for resistance to natural infection by Stagonospora nodorum blotch (SNB) at the 2–3 and 6–7 leaf stages at two sites over two years. There were significant differences in the incidence of SNB between leaf stages in most of the wheat varieties, with resistance being most evident at the 6–7 leaf stage. Separate analyses of the mean values for each generation showed that the genetic mechanism of defense against the pathogen depended upon the leaf stage. At the 2–3 leaf stage, only additive and dominance effects were implicated in the control of SNB for the two crosses at the two sites and for the two replications. For the 6–7 leaf stage, inheritance was more complicated and an epistatic effect was involved. Narrow-sense heritability values (range: 0.63–0.67) were consistent between crosses and leaf stages. These findings indicate a lack of resistance to SNB at the 2–3 leaf stage whereas resistance was observed at the 6–7 leaf stage and involved the genetic mechanisms of plant defense such as epistasis.

Barley breeding for quality improvement in Tunisia

This study was initiated to assess the effectiveness of three selection procedures applied in the early segregating generations of barley crosses for quality traits. The selection procedures were pedigree selection (PS), bulk selection (BS) and single seed descent selection (SSD). Selection was operated in F2’s crosses. Field trials were conducted with 19 F3 crosses of barley in two different environments, a sub-humid environment at Beja and a semi-arid one at Kef. Heading date (HD), thousand kernel weight (TKW), protein content (PC), β-glucan content (BG) and husk percentage (HP) were evaluated. Data were subjected to an additive main effects and multiplicative interaction (AMMI) model to determine the efficiency of each method of selection for the proper environment. The results show that the AMMI model generated predictive optimizing selection method. The pedigree selection was more efficient in high input environment, while the bulk method was very effective for the selection of kernel weight in target environment.

Natural population of oat crown rust in Tunisia.

Oat crown rust, caused by Puccinia coronata f. sp. avenae , is considered the most widespread and damaging disease of oat ( Avena sativa ) in Tunisia . The virulence structure of the natural oat rust population in Tunisia was studied in four areas from 2002 to 2007 using Puccinia coronata resistance genes ( Pc-genes ). The areas are located in northern Tunisia : Afareg, Bourbia, Sedjnen and Ariana. In this survey, Pc38 , Pc39 and Pc68 showed a high level of resistance to natural oat crown rust. But the most important finding in 2004 in Ariana was that the rust was virulent on Pc68 (IT ‘4’). Moreover, in 2002 Sedjnen survey, there was a high degree of virulence to Pc39 (IT ‘3’). In the other areas and other years, Pc68 and Pc39 were highly resistant to natural oat crown rust. Only Pc38 showed a stable high level of resistance to natural oat crown rust in all four areas and during the six years of the study. Areas showing a high degree of similarity were Sedjnen and Afereg (SI=4.5). Ariana and Bourbia showed little similarity to the other areas, and had the greatest dissimilarity to each other (SI=11.30). The virulence phenotypes of the P . coronata natural population in Tunisia are certainly influenced by the alternate host, Rhamnus lycioides which is abundant in the mountains of northwestern Tunisia . A combination of the Pc38 , Pc39 and Pc68 genes will provide a high level of durable protection from crown rust in Tunisia .