Investigations into Physiological, Biochemical, and Histological Modifications in a Vine Decline Associated with Biotic and Abiotic Factors

Tunisian table grape production has significantly increased since two decades due to vineyards regional expansion and yield improvement. But, since several years, decline symptoms on Vitis vinifera have been recorded in some areas. A study case of a vineyard in Naassen area (near to Tunis) was chosen to investigate the disease origin and the physiological, biochemical, and histological modifications associated with vine decline. The investigation revealed characteristic symptoms on leaves, old and young shoots similar to decline symptoms of Grapevine Trunk Diseases. Based on cultural characteristics, laboratory investigations revealed the presence of Phaeomoniella chlamydospora and Phaeoacremonium spp., Diplodia seriata and Botryosphaeria dothidea, from root and shoot samples, respectively. These fungi are known as the main pathogens responsible for the Esca, Black dead arm and Excoriose. Molecular analysis confirmed the identification of Diplodia seriata. Beside morphological alterations on leaves and shoots, symptomatic vines presented significant reductions of 30 and 20% in trunk diameter and bud break rate, respectively, and delayed spring growth compared to healthy ones. Furthermore, roots and stems from declined vines contained 3 times more starch than those from asymptomatic ones. Decline survey revealed a heterogeneous dispersion of symptoms in the vineyard in accordance with water supply. The vines along the edge of vineyards are usually less watered and show more decline symptoms. Decline dynamics in time and space scales have to be considered in order to develop effective management strategies

Adaptation et structuration spatiale des populations méditerranéennes de rouille jaune du blé (Puccinia striiformis f.sp. tritici)

En France, la population de rouille jaune du blé P. striiformis f.sp. tritici (PST) est structurée en deux sous-populations : une population Nord qui provoque des épidémies tous les 3-4 ans, évolue rapidement et présente des pathotypes dotés de nombreuses virulences, et une population Sud plus sporadique et dominée par un pathotype simple (6E16-Av9). Malgré la sensibilité des variétés de blé du Sud de la France aux races du Nord et le potentiel migratoire de PST, cette structuration de la population se maintient. Pour expliquer cette structuration, nous avons testé si (i) les pathotypes du Nord subissent une diminution d agressivité du fait du nombre élevé de virulences qu ils portent, (ii) le pathotype 6E16-Av9 présente une adaptation aux conditions méditerranéennes. Parallèlement, nous nous sommes intéressés à décrire le lien entre cette population du Sud de la France et le reste de la zone méditerranéenne. Les tests de compétition de pathotypes ne différant que par une virulence ont révélé l existence d une moindre fitness chez les pathotypes porteurs d une avirulence inutile. Néanmoins, pour trois cas sur huit, une plus forte agressivité des virulents est observée, nuançant ainsi l importance de l effet d un coût des virulences sur la structuration observée. Des expériences de compétition au champ ont parallèlement confirmé la meilleure adaptation du pathotype 6E16-Av9 à hautes températures (thèse M. Mboup, 2008). L étude génétique de PST autour du Bassin Méditerranéen (AFLP et SSR) confirme l appartenance de la population du Sud à une population Ouest Méditerranéenne et illustre l importance des migrations de spores du Maghreb vers le Sud de l Europe. L identification au Maghreb du gène de résistance Yr8 dans les principales variétés de blé cultivées explique l importance de la virulence correspondante v8 dans les populations méditerranéennes, et l avirulence des pathotypes du Nord (Av8) sur variétés du Sud. L étude d un échantillonnage de PST sur le reste du Bassin Méditerranéen révèle la proximité génétique de la population de l Ouest avec celle du Moyen Orient, dont elle est probablement issue par migration. Ces analyses montrent aussi une diversité supérieure des populations de PST encore plus à l Est, au Pakistan, où la diversité des conditions environnementales biotiques et abiotiques contribuent à l existence et la différentiation de populations contrastées de PST. Les relations phylogénétiques entre les différentes populations échantillonnées et le gradient de diversité Ouest-Est observé apportent des indications sur l origine et la diversification des populations de rouille jaune sur le contient eurasien.The wheat yellow rust is structured in two sub-populations in France : a North population responsible for recurrent epidemics (every 3-4 years) due to pathotypes with complex virulence patterns, and a South population, sporadic and dominated by one simple pathotype (6E16-Av9). Despite the high susceptibility of southern France cultivars to the Northern pathotypes and the presence of spore exchanges between the two areas, this spatial structure is steady over time. In order to explain this structure, we tested if (i) the Northern pathotypes present a fitness penalty due to the unnecessary virulence genes carried; (ii) the southern population has a fitness advantage under Mediterranean conditions. In addition we studied the genetic relationship of the South France PST population with populations from the Mediterranean area. Competition tests between pathotypes differing by one virulence revealed a higher fitness of avirulent isolates. However, for three pairs over eight, an higher aggressiveness was observed for virulent isolates, limiting the impact of the virulence cost in the observed PST structure. Field competitions confirmed the best fitness of 6E16-Av9 pathotype at high temperatures (Mboup PHD, 2008). The genetic study of PST in Mediterranean area (AFLP and SSR) confirmed the belonging of South isolates to a Mediterranean population and highlined the importance of spore migration from North Africa to southern Europe. The identification of the resistance gene Yr8 in the prevalent wheat cultivars in North Africa explains the high frequency of the corresponding virulence v8 in the Mediterranean area, as well as the incapacity of northern pathotypes (Av9) to develop in that area. A complementary sampling revealed the genetic proximity of Mediterranean population with Middle East population, from which it probably originated. An even greatest genetic diversity is depicted, in Pakistan, where probably biotic and abiotic environmental diversities contribute to the existence and the differentiation of contrasted populations. Phylogenetic relations between the populations studied bring some indications on the origin and diversification of PST in the Eurasian continent.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Wheat yellow rust dynamics in Tunisia since 2013 and resistance genes in durum wheat

Wheat yellow rust epidemics, caused by Puccinia striiformis f. sp. tritici (PST) have increased worldwide with the emergence in Western Europe and North Africa of an aggressive strain and tolerant to high temperature (PstS2) since 2004 and exotic strains (Triticale 2006, 2015, Warrior and Kranich) recently. Even though resistant varieties bring to agriculture effective solutions to reduce the use of pesticides, races of the pathogen quickly overcome introduced resistance genes. In this study we determined the virulence combinations using the European and world differential sets and the simple sequence repeat diversity of 94 PST isolates collected in Tunisia since 2013 from the major wheat growing areas. In addition, 39 local Tunisian durum wheat accessions and 109 recombinant inbred lines RILs (F9) were evaluated at the seedling stage against old and new races of PST in order to identify resistant genotypes and markers associated with resistance genes. The results underlined the rapid change in wheat yellow rust population where 3 predominant races, Warrior1 (W1), Warrior- (W-) and Triticale 2006 were detected since 2013. In addition, 10% of the durum wheat accessions were resistant to W1, W- and PstS2. The evaluation of the RILs issued from a cross between Tunisian durum wheat Khiar and Agili39 revealed one major resistance gene against W1 and two minor genes against PstS2. The use of these genes in breeding can improve durability of the genetic control against PS

QTL Mapping combined with comparative analyses identified candidate genes for reduced shattering in setaria italica

Setaria (L.) P. Beauv is a genus of grasses that belongs to the Poaceae (grass) family, subfamily Panicoideae. Two members of the Setaria genus, Setaria italica (foxtail millet) and S. viridis (green foxtail), have been studied extensively over the past few years as model species for C4-photosynthesis and to facilitate genome studies in complex Panicoid bioenergy grasses. We exploited the available genetic and genomic resources for S. italica and its wild progenitor, S. viridis, to study the genetic basis of seed shattering. Reduced shattering is a key trait that underwent positive selection during domestication. Phenotyping of F-2:3 and recombinant inbred line (RIL) populations generated from a cross between S. italica accession B100 and S. viridis accession A10 identified the presence of additive main effect quantitative trait loci (QTL) on chromosomes V and IX. As expected, enhanced seed shattering was contributed by the wild S. viridis. Comparative analyses pinpointed Sh1 and qSH1, two shattering genes previously identified in sorghum and rice, as potentially underlying the QTL on Setaria chromosomes IX and V, respectively. The Sh1 allele in S. italica was shown to carry a PIF/Harbinger MITE in exon 2, which gave rise to an alternatively spliced transcript that lacked exon 2. This MITE was universally present in S. italica accessions around the world and absent from the S. viridis germplasm tested, strongly suggesting a single origin of foxtail millet domestication. The qSH1 gene carried two MITEs in the 5'UTR. Presence of one or both MITEs was strongly associated with cultivated germplasm. If the MITE insertion(s) in qSH1 played a role in reducing shattering in S. italica accessions, selection for the variants likely occurred after the domestication of foxtail millet

Genetic diversity and population structure of Zymoseptoria tritici on bread wheat in Tunisia using SSR markers

Septoria tritici blotch (STB) caused by Zymoseptoria tritici is the primary biotic stress for durum wheat production in Tunisia. The present study was aimed to decipher the genetic diversity and population structure of Z. tritici bread wheat isolates; in the northern regions of Tunisia this pathogen infected exclusively bread wheat. A total of 162 single-spore isolates were sampled during the 2015–2016 growing season from nine naturally infected bread wheat fields at four locations in the three main wheat-growing regions in Tunisia, previously reported as hot spots for Septoria disease (Cap Bon, Bizerte, and Beja). Collected isolates were fingerprinted using twelve polymorphic microsatellite markers to assess the genetic diversity and population structure of Z. tritici. All the microsatellite loci were polymorphic and a high genetic diversity was observed within the whole population. The highest Nei’s index value (0.42), Shannon Index (0.84) and private allele numbers (36) were found at the El Haouaria location (Cap Bon region). Furthermore, a moderate genetic differentiation within and among the surveyed locations (73% and 27%) was confirmed by analysis of molecular variance (AMOVA). On the other hand, the STRUCTURE program was shown to be less sensitive in revealing genetic structure especially at low levels of diversity. Thus, information on the genetic structure of the pathogen population collected from bread wheat is useful for designing and implementing durable and effective management strategies