Insights on gene expression response of a characterized resistant genotype of Solanum commersonii Dun. against Ralstonia solanacearum

Solanum commersonii is a wild species related to the cultivated potato. Some S. commersonii genotypes have been proven to be resistant to the pathogenic bacteria Ralstonia solanacearum, which causes damage in potato and other economically important crops. Here an expression analysis of the response of a resistant S. commersonii genotype against R. solanacearum was performed using microarrays. The aims of this work were to elucidate the molecular processes involved in the interaction, establish the timing of the response, and contribute to identify genes related to the resistance. The response to the treatment was already initiated at 6 h post-inoculation (hpi) and was established at 24 hpi; during this period, a high number of genes was differentially expressed and several candidate genes for the resistance of S. commersonii to R. solanacearum were identified. At an early stage, the photosynthetic process was highly repressed and several genes encoding proteins related to reactive oxygen species (ROS) production were differentially expressed. The induction of ERF and ACC-oxidase genes related to the ethylene pathway and PR1 related to the salicylic acid pathway suggested the induction of both pathways, and back up the previously reported hemibiotrophic nature of the pathogen. Five genes related to plant defence and observed to be differentially expressed at the first two time points were validated by real time PCR. This work gives a glimpse to the molecular processes involved in S. commersonii resistance and identifies the species as a valuable genetic source for potato breeding against bacterial wilt.     

Detection of PVY extreme resistance genes in potato germplasm from the uruguayan breeding program

Breeding goals in potato programs encompass several important commercial traits such as market aspects (skin color, eye depth, shape), category use (fresh or processed), yield, crop duration, and pest and disease resistance. In light of medium- and long-term changes in trait requirements, breeders rely on a range of wild and commercial germplasm in their efforts to reach the multiple objectives that determine the success of a new variety. Readily selectable markers for the recognition of multiple introgressed traits in breeding populations would therefore be practical high-value tools. In subtropical countries, warm climate and the continuous cropping of potato promote high vector pressure and the spread of viruses, rendering seed certification schemes difficult.Potato virus Y (PVY) constitutes a constant problem in several developing countries and it was recently reported as a challenge for seed production in the U.S.A. and Spain, resulting in rejection of seed lots in certification programs. Here we report the simultaneous use of two molecular markers to identify genes for extreme resistance to PVY in the Uruguayan potatobreeding program germplasm. Simplicity and compatibility of the marker system (allele specificity) were emphasized in implementing a reliable and efficient procedure. Forty-four percent of the genotypes tested were shown to carry extreme resistance to PVY, in the majority of cases fromSolanum tuberosum ssp.andigena (Ry_adg). Furthermore, a single marker originating fromSolanum stoloniferum (M45) could be used to recognize both Ry_sto and Ry_adg. The molecular phenotype data corresponding to M45-Ry genotypes was in accordance with virus field exposure observations of resistance.     

Ecology-based analysis of a recent association between Spartium junceum and 16SrV phytoplasma

An outbreak of Spartium witches’ broom (SpaWB) in Sicily prompted us to identify and characterize associated phytoplasmas. Over 80 samples of Spanish broom (Spartium junceum) and around 270 individuals of the potential vector Livilla spectabilis were collected and analysed. Single and mixed infections of 16SrV and ‘Candidatus Phytoplasma spartii’ were detected in Spanish broom samples and for the first time in L. spectabilis. The 16SrV isolates were further characterized by multilocus sequence typing (MLST) to determine their phylogenetic relationship with flavescence dorée phytoplasma (FDp) and to evaluate the risk of host-jumping to grapevine. Phylogenetic analysis of most of the analysed genes using the MLST approach grouped S. junceum 16SrV-C isolates with FDp isolates infecting grapevine and Scaphoideus titanus. Notably, phylogenetic analysis of the vmpA gene clustered the S. junceum isolates with FDp genotypes transmitted by S. titanus. This study extends the knowledge of SpaWB epidemiology, focusing on the possible risk of a 16SrV host jump from Spanish broom to grapevine. Spanish broom was identified as a reservoir and potential inoculum source of phytoplasmas that cause severe disease in cultivated crops. Furthermore, the L. spectabilis psyllid may be involved in the epidemiology of this 16SrV-C phytoplasma, although in the absence of in vivo transmission trials. The study further confirms the strong ability of phytoplasmas to adapt to new hosts and vectors, thus leading to potential phytosanitary emergencies.     

柑橘类病毒的分子鉴定与分型

 【目的】检测湖南地区柑橘所携带的柑橘类病毒类型,并鉴定柑橘类病毒的亚型。【方法】以田间柑橘枝条韧皮部为试材,提取总RNA,反转录成cDNA,再用不同类型类病毒的特异引物进行PCR扩增,鉴定出各个样品所携带的柑橘类病毒类型;通过测序分析各类型的序列,并与国内外报道的序列进行同源性分析,确定所测样品的亚型。【结果】建立了CEVd、CVdII、CVdⅢ等柑橘类病毒的RT-PCR检测方法。在5个供试样品中检测出3种类型的柑橘类病毒,即柑橘裂皮病类病毒（citrus exocortis viroid,CEVd）、柑橘类病毒Ⅱ型（citrus viriodⅡ,CVdⅡ,又名hop stunt viroid,HSVd）和柑橘类病毒Ⅲ型（citrus viriodⅢ,CVdⅢ）,其中CVdⅡ和CVdⅢ为国内首次发现。亚型分析表明CVdⅡ可能为新的亚型;CVdⅢ为b亚型,可能具有矮化功能。【结论】在中国鉴定出3种类型的柑橘类病毒,CEVd与国内已报道的序列完全一致,其中CVdⅡ和CVdⅢ为首次在中国发现;检测到的CVdⅡ可能为新的亚型。     

Genetic progress of oats in Italy

The genetic gain of oats in Italy over the past 40 years was evaluated using 14 cultivars belonging to three different groups: (i) five cultivars derived from local populations at the beginning of the oat breeding in Italy; (ii) four foreign cultivars, introduced in Italy in the 1980s; (iii) five modern cultivars, selected through specific breeding programmes. The genotypes were tested for 2 years in three locations characterised by different climatic conditions and agricultural practices; furthermore in one location in Southern Italy, irrigated and rainfed plots were compared. Genetic gain was estimated equal to 3.6 g m⁻² y⁻¹ based on eight environments. The performance of the most recent cultivars was high under both irrigated and rainfed conditions, showing a good adaptation of these genotypes to both fertile and drought prone environments. Finally, yield increase in oats was found to be negatively correlated with plant height and positively correlated with test weight and seed weight.     

Use of chlorophyll fluorescence to evaluate the cold acclimation and freezing tolerance of winter and spring oats

The efficiency of the excitation capture by open Photosystem II (PSII) reaction centres was measured by the F_v/F_m ratios in a collection of winter and spring oats in order to assess the effects of hardening and freezing on the functionality of PSII and also the suitability of a chlorophyll fluorescence‐based method to screen oat cultivars for frost tolerance. A significant reversible decrease in F_v/F_m was found in all genotypes during acclimation to low, non‐freezing temperatures. F_v/F_m analysis appears to be an attractive test for the evaluation of frost tolerance in oats, being rapid, non‐invasive and capable of monitoring a trait related to a crucial stage in the acquisition of frost tolerance. It is more sensitive and precise than other standard methods and highly correlated with field‐evaluated frost damage. The measurements made during recovery 1 or 2 days after stress when the visual symptoms are not yet expressed, were especially advantageous because of the large variability in genotype response. The r‐values (close to 0.8) were reduced due to the non‐standard behaviour of the winter cultivar ‘Aintree’. The cold acclimation response of this genotype has been analysed in detail and the limits of artificial freezing tests are discussed.     

Determinants of barley grain yield in a wide range of Mediterranean environments

Barley grain yield in rainfed Mediterranean regions can be largely influenced by terminal drought events. In this study the ecophysiological performance of the ‘Nure’ (winter) × ‘Tremois’ (spring) barley mapping population (118 Doubled Haploids, DHs) was evaluated in a multi-environment trial of eighteen site–year combinations across the Mediterranean Basin during two consecutive harvest years (2004 and 2005). Mean grain yield of sites ranged from 0.07 to 5.43 t ha⁻¹, clearly dependent upon both the total water input (rainfall plus irrigation) and the water stress index (WSI) accumulated during the growing season. All DHs were characterized for possessing molecular marker alleles tagging four genes that regulate barley cycle, i.e. Vrn-H1, Vrn-H2, Ppd-H2 and Eam6. Grain yield differences were initially interpreted in terms of mean differences between genotypes (G), environments (E), and for each combination of genotype and environment (GE) through a “full interaction” ANOVA model. Variance components estimates clearly showed the greater importance of GE over G, although both were much lower than E. Alternative linear and bilinear models of increasing complexity were used to describe GE. A linear model fitting allelic variation at the four genes explained genotype main effect and genotype × environment interaction much better than growth habit itself. Adaptation was primarily driven by the allelic constitution at three out of the four segregating major genes, i.e. Vrn-H1, Ppd-H2 and Eam6. In fact, the three genes together explained 47.2% of G and 26.3% of GE sum of squares. Grain yield performance was more determined by the number of grains per unit area than by the grain weight (phenotypic correlation across all genotypic values: r = 0.948 and 0.559, respectively). The inter-relationships among a series of characters defining grain yield and its components were also explored as a function of the length of the different barley developmental phases, i.e. vegetative, reproductive, and grain filling stages. In most environments, the best performing (adapted) genotypes were those with faster development until early occurrence of anthesis. This confirmed the crucial role of the period defining the number of grains per unit area in grain yield determination under Mediterranean environments.