A random amplified polymorphic DNA (RAPD) molecular marker for the Tm-2 a gene in tomato

Summary A RAPD marker, linked to the Tm-2 ^agene engendering TMV resistance in tomatoes, was identified. The validity of the RAPD marker was corroborated by screening several tomato varieties, and correctly identifying those which carried Tm-2 ^a, as well as by F₂ segregation analysis. All tested resistant varieties descending from a common Lycopersicon peruvianum/esculentum ancestor, LA1791, exhibited this marker.     

The potential of ripening mutants for extending the storage life of the tomato fruit

Summary The effect of the fruit ripening mutants rin, gr, nor and Nr on storage life and pigmentation was investigated in homozygous material, in heterozygous F₁ combinations between the mutants with the colour mutant hp and with the normal cv. Kewalo. Crosses with nor showed a 3-to 5-fold increase in storage life in comparison with the normal cv. or with hp. Maximum pigmentation of the fruits of crosses with nor was pale-red with vineripened fruit and pink with fruit harvested at the breaker stage and ripened on the shelf. The ripening inhibitory effect of rin in the different F₁ combinations was less pronounced than that of nor, and the colour of the fruits was improved. Fruits of the F₁ cross between rin and nor showed greatly improved storage life and developed pink or pale red colour. Most heterozygotes with hp showed improved pigmentation. Problems anticipated in utilizing ripening mutants in breeding for improved keeping quality are discussed.     

Colloidal jamming at interfaces: a route to fluid-bicontinuous gels

Colloidal particles or nanoparticles, with equal affinity for two fluids, are known to adsorb irreversibly to the fluid-fluid interface. We present large-scale computer simulations of the demixing of a binary solvent containing such particles. The newly formed interface sequesters the colloidal particles; as the interface coarsens, the particles are forced into close contact by interfacial tension. Coarsening is markedly curtailed, and the jammed colloidal layer seemingly enters a glassy state, creating a multiply connected, solidlike film in three dimensions. The resulting gel contains percolating domains of both fluids, with possible uses as, for example, a microreaction medium.     

Australian Uromyces viciae-fabae: Host and nonhost interaction among cultivated grain legumes

Uromyces viciae-fabae, rust of faba bean, parasitizes other legume crops such as lentils (Lens culinaris) and field peas (Pisum sativum) in some environments. In this study we examined the host range of two Australian isolates of U. viciae-fabae collected and purified from a faba bean crop and classified as U. viciae-fabae ex V. faba. Field pea (P. sativum), chickpea (Cicer arientinum), lupin (Lupinus spp.), lentil (L. culinaris), and mung bean (Vigna radiata) genotypes were tested with these isolates, as well as resistant and susceptible genotypes of the faba bean host. Race specificity for these two pathogen isolates was observed on Vicia faba, with two faba bean genotypes showing partial resistance. Both U. viciae-fabae isolates also colonized field pea seedlings and successfully produced uredinia under glasshouse conditions, despite this fungus not being known as a pathogen of Australian field pea crops. No sporulation of either isolate of U. viciae-fabae ex V. faba was observed on any of the remaining legume species tested. However, obvious differences in fungal growth were observed, ranging from small infection sites with very rare haustorium formation in mung bean to more extensive growth and the development of potential uredinial structures in chickpea. These observations are discussed in relation to the phylogenetic relationship of these host and nonhost species.     

A SCAR marker linked to the ToMV resistance gene, Tm22, in tomato

A polymerase chain reaction (PCR)-based co-dominant marker was developed which is tightly linked to Tm2². This dominant locus confers resistance to ToMV in tomato. Random-amplified-polymorphic DNA (RAPD) screening was carried out with DNA from ToMV-susceptible and resistant tomato near-isogenic lines. A polymorphic band linked to ToMV resistance was observed. The polymorphic fragment was cloned and the DNA sequences of both ends determined. Specific PCR primers were designed from these sequences. PCR amplification with the specific primers resulted in an amplified band (SCAR) in both susceptible and resistant tomato lines. The amplified band from the susceptible lines could, however, be discerned from that of the resistant ones after cleavage with the restriction enzyme Hind III. In an F₂ population of 90, the polymorphic markers co-segregated with susceptibility or resistance, as determined by biological assays for ToMV resistance. The reported SCAR marker is linked to ToMV resistance not only in cultivars derived from American lineage, but also from European lineage. This method enables the distinction of homozygous and heterozygous individual plants in segregating populations, and provides a convenient and rapid assay for both selection and quality control during breeding programs and hybrid seed production, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reduced Germination and Seedling Vigor of Weeds with Root Extracts of Maize and Soybean,and the Mechanism Defined as Allelopathic

Journal of Crop Science and Biotechnology - Due to the negative consequences of synthetic herbicides use and their reducing effectiveness due to development of resistant weeds, promotion of...     

Recurrent breeding method enhances the level of blackspot (Didymella pinodes (Berk. & Blox.) Vestergr.) resistance in field pea (Pisum sativum L.) in southern Australia

Blackspot, caused by Didymella pinodes (Berk. & Blox.)Vestergr., is one of the most important diseases of field pea, causing significant reduction in seed yield and quality in southern Australia and in other parts of the world. Development of resistant germplasm has been slow because of the low level of resistance found in the available germplasm, poor reliability of screening methods and the polygenic nature of inheritance. Crosses were made between agronomically suitable lines and resistant germplasm from different sources. Their progeny were advanced through the single seed descent method and single plants were selected at F₄/F₅. The F₄/F₅ derived lines were screened against blackspot in the field under disease pressure and evaluated for grain yield at multilocations over 2 years. Despite the low level of resistance in the parental germplasm, the level of resistance has increased significantly in the new germplasm. Many of the resistant lines were late and low yielding, but lines with higher resistance and early flowering and high yield potential were also identified indicating that the disease resistance, adaptation and yield potential can be combined. However, the resistance identified in this study is only partial and suitable agronomic practices may need to be supplemented to minimise the yield loss and enhance the benefits of this partial resistance.     

Genetic relationships among populations of Gibberella zeae from barley, wheat, potato, and sugar beet in the upper Midwest of the United States

Gibberella zeae, a causal agent of Fusarium head blight (FHB) in wheat and barley, is one of the most economically harmful pathogens of cereals in the United States. In recent years, the known host range of G. zeae has also expanded to noncereal crops. However, there is a lack of information on the population genetic structure of G. zeae associated with noncereal crops and across wheat cultivars. To test the hypothesis that G. zeae populations sampled from barley, wheat, potato, and sugar beet in the Upper Midwest of the United States are not mixtures of species or G. zeae clades, we analyzed sequence data of G. zeae, and confirmed that all populations studied were present in the same clade of G. zeae. Ten variable number tandem repeat (VNTR) markers were used to determine the genetic structure of G. zeae from the four crop populations. To examine the effect of wheat cultivars on the pathogen populations, 227 strains were sampled from 10 subpopulations according to wheat cultivar types. The VNTR markers also were used to analyze the genetic structure of these subpopulations. In all populations, gene (H = 0.453 to 0.612) and genotype diversity (GD = or >0.984) were high. There was little or no indication of linkage disequilibrium (LD) in all G. zeae populations and subpopulations. In addition, high gene flow (Nm) values were observed between cereal and noncereal populations (Nm = 10.69) and between FHB resistant and susceptible wheat cultivar subpopulations (Nm = 16.072), suggesting low population differentiation of G. zeae in this region. Analysis of molecular variance also revealed high genetic variation (>80%) among individuals within populations and subpopulations. However, low genetic variation (<5%) was observed between cereal and noncereal populations and between resistant and susceptible wheat subpopulations. Overall, these results suggest that the populations or subpopulations are likely a single large population of G. zeae affecting crops in the upper Midwest of the United States.     

Seed Number,Specific Gravity and External Appearance of Hollow Tomato Fruits

Experiments were carried out in Israel over several years with outdoor winter tomatoes, cv. Moneymaker. It was concluded that generally no correlation exists between the average number or weight of seeds per fruit and the frequency or grade of hollowness. The separation of regular, globe-shaped from irregularly shaped fruit substantially reduced the percentage of hollowness of the samples. The immersion of tomato fruits in tap or distilled water allowed satisfactory separation between hollow fruits, most of which floated on the surface, and normal fruits which mostly sank to the bottom.