Genetic characterization by fluorescent AFLP of Pseudomonas savastanoi pv. savastanoi strains isolated from different host species

The genetic diversity of 71 Pseudomonas savastanoi pv. savastanoi strains isolated from different host species and from diverse geographical regions was determined by fluorescent amplified fragment length polymorphism (f-AFLP) analysis. The study was carried out using three different selective primer combinations. Strains of P. syringae pv. syringae , P. syringae pv. phaseolicola , P. syringae pv. glycinea , P. syringae pv. tagetis and P. amygdali were also included as outgroups. Based on cluster analysis of f-AFLP data, all P. savastanoi pv. savastanoi strains showed a high degree of similarity, grouping in a cluster and forming a taxon clearly separate from outgroup strains. AFLP analyses failed to support placing strains of P. savastanoi pv. savastanoi , P. syringae pv. phaseolicola and P. syringae pv. glycinea in the same species. Strains of P. savastanoi pv. savastanoi formed subclusters that correlated with the host species. Strains identified within these subclusters were related to the geographical region where the strains were isolated. Strains of P. savastanoi pv. savastanoi from olive were divided into two subclusters. Strains from oleander were differentiated from those from ash and were divided into two additional subclusters, distinct from olive strains. Three strains isolated from jasmine showed a high level of similarity among them but, at a lower Dice similarity coefficient, were linked to a subcluster including olive strains. Finally, two strains isolated from privet were similar to strains from olive and were included in the same subcluster.     

Doubled-haploid versus single-seed descent and S1-family variation for testcross performance in a maize population

Progress made in the in situ gynogenesis technique since 1990 now allows production of a high number of maize (Zea mays L.) doubled-haploid (DH) lines. The aim of the study was to compare DH lines versus selfing lines for testcross performance. DH and single-seed descent (SSD) lines were produced from random S₁ progenies of a broad-base population. For grain yield, kernel moisture, plant height, ear height and leaf length, the three population means were similar. Except for kernel moisture, the genetic variance of DH lines was nearly twice as high as the genetic variance of S₁ families, as expected. On the other hand, genetic variance among SSD lines was only 1.5 times higher than the genetic variance of S₁ families. This lower variance could be due to a selection bias in the method of production of SSD lines. However, for all traits, heritability of SSD or DH lines was higher than heritability of S₁ families. Epistasis effects in DH progenies were not significant. The consequence was a high correlation between S₁ testcross progenies and DH or SSD testcross progenies, meaning that the S₁ testcross value can be used to select the best families from which DH lines will be extracted. As a whole, the observed variation in DH lines appeared to be more in accordance with the observed variation among S₁ families than with the observed variation among SSD lines.     

Morphological characterization of the IVIA persimmon (Diospyros kaki Thunb.) germplasm collection by multivariate analysis

Diospyros kaki Thunb. originated in Eastern Asia, as evidenced of its culture in China as early as several centuries B.C. In the seventh century, persimmon was introduced to Japan and later, in the fourteenth century to Korea. There is no information about persimmon culture in Europe until the seventeenth century, with the spread over the world occurring in the eighteenth century. The genus Diospyros contains more than 400 species, with levels of ploidy ranging from diploid (2n = 2x = 30) up to nonaploid (2n = 9x = 135). The primary economic crop species is Diospyros kaki Thunb., which is mainly hexaploid (2n = 6x = 90) and includes hundreds of cultivars. Although a relatively recent introduction in Europe, the species has adapted well, and the genetic diversity have been expanded with culture and selection for the past 200 years in the Mediterranean basin. These locally adapted cultivars were evaluated with cultivars from Asian origin in a germplasm collection established at IVIA in Valencia, Spain. In this paper 27 cultivars from the IVIA collection were studied by multivariate analysis, and 37 variables were analyzed using a Principal Components Analysis and cluster analysis following the method UPGMA. Studies on correlations and significance among variables identified the most relevant ones, and thus provided information for a future core collection.     

Detection of Actinobacillus pleuropneumoniae Infection in Pigs

It is difficult to control the spread of porcine haemophilus pleuropneumonia caused by Actinobacillus pleuropneumoniae because there is no sensitive and specific way to accurately determine whether or not a pig herd is infected. This paper reports bacteriological and serological techniques used to detect A. pleuropneumoniae infection in pigs from a herd with endemic disease.

The bacteria were isolated from the anterior nasal mucosa of grower pigs, but not from younger or older pigs. Bacteriological culture of several tissues from the respiratory tract showed that nine of ten young finishing pigs were infected, but culture of lung tissue from slaughtered hogs detected infection in only 39 of 288 (13.5%). Both cooler storage temperature and use of selective medium prolonged the time that lung tissue could be stored and the organism still recovered. An enzyme-linked immunosorbent assay detected serotype-specific antibodies in serum of infected pigs.

     

Influence of variety on the within-plant distribution of cassava green spider mite (Acari: Tetranychidae), and leaf anatomical characteristics and chemical components in relation to varietal resistance

The within-plant distribution of the cassava green spider mite, Mononychellus tanajoa Bondar, and the anatomical characteristics and the chemical components relating to varietal resistance of cassava, were studied using 11 cassava genotypes with varying levels of resistance for two dry seasons and one wet season. The results show that M. tanajoa aggregates on the top leaves of cassava at low levels of resistance as compared with a more even within-plant distribution at higher levels of resistance. Thus, for accurate sampling of mite populations, it might be important to consider young and old leaves, not just the young leaves, in fields containing resistant and susceptible cassava genotypes. Correlations between the anatomical characteristics and mite population density and damage scores were not consistent across months, either within or over seasons. This suggests that leaf anatomical characteristics may not be important in the varietal resistance of cassava to M. tanajoa. During the dry season, mite population density was positively correlated with leaf nitrogen, potassium and phosphorus and negatively correlated with leaf calcium and fat. Only calcium was negatively associated with mite damage at the peak of the dry season (January 1993 and 1994). Breeding cassava genotypes with high levels of leaf calcium and fat, and low levels of leaf nitrogen, potassium and phosphorus, may improve the level of resistance to M. tanajoa.     

Tuta absoluta,a South American pest of tomato now in the EPPO region: biology,distribution and damage

Tuta absoluta (Meyrick) is an invasive pest of tomato native to South America, where it is responsible for extensive damage. It rapidly spread into several European countries, becoming a key pest. Knowledge of its main biological traits can be used to develop effective plant protection management strategies. It is a multivoltine species with a homodynamous behaviour, and the length of its life cycle depends on environmental conditions, particularly temperature. The larvae feed and develop inside tomato leaves, stems and fruits throughout the entire growing cycle. The adults have crepuscular habits, and in Mediterranean conditions they can be easily detected throughout the year. Damage is directly related to the reduction of plants' photosynthetic capacity and of production levels in both protected and open‐field tomato crops; indirect damage can be also caused by secondary infections, with pathogens developing on the infested plant and fruit tissues.     

Genetic improvement of the Pacific oyster Crassostrea gigas (Thunberg) in Australia

The Pacific oyster industry in Australia is derived from importations from Japan in the late 1940s and early 1950s to Tasmania and is almost completely hatchery based. This makes it a good target for developing and deploying genetically improved strains. An allozyme survey comparing hatchery stocks with self‐recruiting Tasmanian stocks and with two collections from Japan found abundant variation and no significant evidence of allele loss. The subsequent selection programme (initiated in the summer of 1996/97) had several strands. We wanted to take advantage of the increased power that marker‐assisted selection could bring and, therefore, needed to develop a linkage map and isolate flanking markers around quantitative trait loci (QTLs). Several types of markers (allozymes, microsatellites and AFLPs) were used, and single‐pair crosses were set up; QTLs have been detected. Conventional selection programmes, one based on mass selection and one on family selection, have been established. Triploid Pacific oysters produced via chemical means have been available for several years, but rates of triploidy achieved by such means are usually less than 100%. In 1999, we will assess whether our tetraploid 2‐year‐old broodstock can be crossed with diploids to give 100% triploid offspring.