Salah Rezgui

Frequency of mutations associated with fungicide resistance and population structure of Mycosphaerella graminicola in Tunisia

The occurrence of fungicide resistance in Mycosphaerella graminicola populations from Tunisia was investigated by examining mutations known to be associated with strobilurin and azole resistance. Few mutations associated with fungicide resistance were detected. No evidence for strobilurin resistance was found among 357 Tunisian isolates and only two among 80 sequenced isolates carried mutations associated with azole resistance. A network analysis suggested that these mutations emerged independently from mutations found in previously described European populations. The population genetic structure of M. graminicola in Tunisia was analyzed using variation at 11 microsatellite loci. Populations in Tunisia were characterized by high gene and genotype diversity. All populations were in gametic equilibrium and mating type proportions did not deviate from the 1:1 ratio expected under random mating, consistent with regular cycles of sexual reproduction. In combination with a high degree of gene flow among sampling sites, M. graminicola must be considered a pathogens with high evolutionary potential. Thus, control strategies against Septoria blotch in Tunisia should be optimized to reduce the emergence and spread of resistant isolates.

Calcareous impact on arbuscular mycorrhizal fungus development and on lipid peroxidation in monoxenic roots

The present work underlined the negative effects of increasing CaCO(3) concentrations (5, 10 and 20 mM) both on the chicory root growth and the arbuscular mycorrhizal fungus (AMF) Glomus irregulare development in monoxenic system. CaCO(3) was found to reduce drastically the main stages of G. irregulare life cycle (spore germination, germinative hyphae elongation, root colonization, extraradical hyphae development and sporulation) but not to inhibit it completely. The root colonization drop was confirmed by the decrease in the arbuscular mycorrhizal fungal marker C16:1ω5 amounts in the mycorrhizal chicory roots grown in the presence of CaCO(3). Oxidative damage evaluated by lipid peroxidation increase measured by (i) malondialdehyde (MDA) production and (ii) the antioxidant enzyme peroxidase (POD) activities, was highlighted in chicory roots grown in the presence of CaCO(3). However, MDA formation was significantly higher in non-mycorrhizal roots as compared to mycorrhizal ones. This study pointed out the ability of arbuscular mycorrhizal symbiosis to enhance plant tolerance to high levels of CaCO(3) by preventing lipid peroxidation and so less cell membrane damage.

Estimating grain yield losses caused by septoria leaf blotch on durum wheat in Tunisia

Septoria leaf blotch (SLB), caused by Zymoseptoria tritici (Desm.) Quaedvlieg & Crous, 2011 (teleomorph: Mycosphaerella graminicola (Fuckel) J. Schrot.), is an important wheat disease in the Mediterranean region. In Tunisia, SLB has become a major disease of durum wheat (Triticum turgidum L. subsp. durum [Desf.] Husn.) particularly during favorable growing seasons where significant yield losses and increase of fungicides use were recorded over the last three decades. The objectives of this study were to evaluate the effect of SLB severity on grain yield of new elite durum wheat breeding lines and to measure the relative effect of fungicide control on grain yield. Experiments were conducted during 2007-2008 and 2008-2009 cropping seasons. A set of 800 breeding lines were screened for reaction to SLB under natural infection at Beja research station. To estimate the disease effect, correlation between disease severity at early grain filling stage and grain yield was performed. Results showed that susceptible varieties yield was significantly reduced by SLB. Average yield reduction was as high as 384 and 325 kg ha-1 for every increment in disease severity on a 0-9 scale in both seasons, respectively. A negative correlation coefficient varied between -0.61 and -0.66 in both seasons. Treated and untreated trials conducted during 2008-2009 and 2009-2010 showed that yield of treated plots increased by 50% on the commonly cultivated susceptible varieties. The results of this investigation suggested that septoria incidence is related to large grain yield losses particularly on susceptible high yielding cultivars. However, appropriate fungicide application at booting growth stage could be beneficial for farmers. The development and use of more effective fungicide could be sought to alleviate the disease effects and therefore could be considered as a part of the integrated pest management and responsible use strategy on septoria leaf blotch in Tunisia.

Pathotype and microsatellite analyses reveal new sources of resistance to barley scald in Tunisia

We examined the variation and relationships between pathogenicity and a microsatellite-based haplotype in 79 Tunisian Rhynchosporium secalis isolates that were collected from the most commonly cultivated barley populations in Tunisia, Rihane cv. and local landraces, with the goal of finding genes that might be used to monitor resistance to scald. Isolates could be classified into three distinct virulence groups based on artificial inoculation of 19 differential cultivars with known scald resistance genes. The resistance gene BRR2 carried by the Astrix differential cultivar appeared to be the most effective in Tunisia. Pathotypes sampled from the Rihane host were more virulent than those sampled from local barley landraces. Because some differential cultivars that carried the same resistance genes showed different reaction patterns to 48 of the isolates, we postulated that other unknown resistance gene(s) specific to Tunisian isolates may be prevalent and could be used in Tunisian barley breeding programs. Microsatellite fingerprinting allowed the detection of 11 alleles linked to the virulence and pathogenic identification of 52% of the tested isolates. Thus, microsatellite analysis may provide a rapid tool for pathogen detection, without an inoculation step that requires long incubation periods before ultimate disease assessment.

Sélection de lignées d’orge (Hordeum vulgare L.) pour leur résistance au barley yellow dwarf virus (BYDV) et évaluation de leurs performances agronomiques

Abstract: Le virus de la jaunisse nanisante de l’orge ou « barley yellow dwarf virus » (BYDV) est connu comme étant le virus le plus important se répandant sur les céréales. En Tunisie, les contaminations peuvent dépasser 40 % sur orge dans certaines régions. La sélection de génotypes résistants constitue le moyen le plus propice pour la lutte contre le BYDV. Ainsi, une sélection à partir de 10 populations d’orge F2 fournis par le Centre International de Recherche Agricole dans les Zones Arides (ICARDA) dont certains parents sont porteurs du gène de résistance Yd2, a été entreprise. De la F2 à la F5, 198 lignées avancées ont été sélectionnées pour leur résistance. Cette résistance a été évaluée, sur les plans symptomatique, sérologique et moléculaire par l’utilisation du marqueur Ylp (CAPS) associé au gène cible (Yd2). Une évaluation agronomique de ces lignées a été réalisée durant la campagne 2006--2007, à Béja (région subhumide) et au Kef (région semi-aride). Le choix particulièrement basé sur le rendement en grains a porté sur 25 lignées qui étaient toutes supérieures au cultivar sensible « Rihane » mais dont huit seulement dépassent l’autre cultivar sensible « Manel ». Parmi ces lignées, 16 pourraient être destinées à l’exploitation à double fin (grains et paille) alors que deux ont montré une souplesse d’adaptation à la fois aux conditions semi-arides et subhumides.

Incorporation of β-Glucans into Pasta Extracted from Two Tunisian Barley Cultivars

Abstract The main objective of this study is to extract water-soluble barley (1→3) and (1→4)-β-d-glucans (β-glucans) from milled seeds of two common Tunisian barley cultivars (Manel and Rihane). A mixture of these barley β-glucans was added to spaghetti made with semolina of durum wheat. Cooking quality related traits of functional spaghetti made with durum wheat semolina was investigated. Four spaghetti samples prepared from semolina added with β-glucan ratios: 1, 3, 5 and 7 g/100 g; were developed and compared to the check. Samples were assessed for water absorption, optimal cooking time, cooking loss, swelling index, colour, carotenoids pigments, hardness, moisture, proteins and ash content. Results indicated that spaghetti added with Tunisian barley β-glucans have a good brightness and acceptable general aspect compared to the check. Spaghetti samples showed lower moisture and proteins contents and higher mineral contents and cooking loss. Lower swelling index and hardness properties were noted in incorporated pasta.

Seed Quality-Related Traits Influence Germination of Helianthus annuus L. Grown Under Three Levels of Water Supply

In order to select a suitable sunflower genotype with a high germination rate and germination speed under controlled field conditions, a selection program was launched. The effect of seed quality-related traits on the emergence time, germination percentage (G%), and germination index (GI) using three water regimes (rainfed, 50% water supply, 100% water supply) was assessed for six lines selected from an adapted sunflower population: C8.3.1.2 (Line1), 64A71 (Line 2), C7.3.2.2 (Line 3), C1.3.1.1 (Line 4), C5.2.3.2 (Line 5), and C31.1.1.2 (Line 6). Total seed crude protein (SCP), seed oil content (SOL), kernel-grain ratio (KGR), hull-kernel ratio (HKR), seed length:width ratio (LWR), and 100-seed weight (HSW) were assessed. Genotype and water regime independently affected G%, which ranged from 31%–72%, 39%–96%, and 35%–89% for rainfed, 50% water, and 100% water regimes, respectively. All lines showed the highest G% at 50% water supply except for C7.3.2.2. Except for C7.3.2.2 and C1.3.1.1, G% decreased when the water level increased. There was a significant positive correlation between KGR and G% in 50% and 100% regimes (r = 0.63, r = 0.59, respectively; P < 0.01). However, the association was significantly negative between HKR and G% in 50% and 100% regimes (r = −0.47, r = −0.63, respectively; P < 0.01). The G% in the 100% regime was also significantly and positively correlated with SCP (r = 0.49; P < 0.05). Compared with the 50% and 100% regimes, G% in the rainfed treatment was not correlated with any seed-related traits. The HKR, KGR, and SCP can be considered to be the most selective criteria since they show a significant correlation with the 50% and 100% water regimes. In conclusion, 50% water supply is the most adapted regime for most of the sunflower genotypes examined in our study.