Pithiness and Growth of Radish Tubers as Affected by Irradiance and Plant Density

Pithiness in radish tubers (Raphanus sativus L.) is a syndromewhere xylem parenchyma cells die and are filled with air. Featuresassociated with rapid tuber growth such as large cells, greatdistances between strands of vascular tissue and rupture ofxylem vessels have been suggested to induce pithiness. The objectiveof this study was to analyse the extent to which pithiness inradish was related to tuber growth. Growth rates were variedby altering irradiance and plant density. In addition, the relationshipbetween pithiness and tuber growth (length, diameter, freshmass) was investigated in batches of plants grown under identicalconditions. The growth rates of shoot and tuber strongly increased withincreasing inter-plant distance and irradiance. Our resultssuggest a ‘true’ effect of assimilate supply ondry matter partitioning, as not only the ratio between shootand root dry mass, but also the slope of this relationship decreasedwith increasing irradiance and inter-plant distance. Withina treatment the ratio between tuber growth and shoot growthremained constant with plant age. Increase in length of thetuber did not appear to be an important factor in inducing pithiness.Within a batch of plants, a positive correlation between tuberdiameter and pithiness was observed only for tubers smallerthan 14 mm. An increase in both irradiance and inter-plant distanceincreased tuber size (diameter, mass) and pithiness, but theeffects on pithiness could not be ascribed only to differenttuber sizes. Pithiness strongly increased with plant age andit was concluded that pithiness occurred, to a great extent,according to genetic programming. The data showed that for treatmentswhich affect tuber growth, conclusions about their effects onpithiness depend on whether comparisons were made at the sametuber size or the same time, explaining apparent contradictionsin the literature. Raphanus sativus L.; radish; pithiness; genetic programming; cell death; light; plant density; growth rate; dry matter partitioning; shoot; tuber     

Reconstruction of fig wasp mating structure: how many mothers share a fig?

Abstract.  1. Fig wasps (Hymenoptera: Agaonidae) represent an important model system for studies of sex ratio evolution, mainly because they may adjust their sex ratios in response to the numbers of ovipositing females (foundresses) that enter a fig and their clutch size.
2. Until recently, it was assumed that all foundresses fail to re-emerge from the figs that they have entered to oviposit, but there is increasing evidence that such re-emergence may be routine. The common practice of counting the number of dead foundresses present in a fig in order to deduce the number of foundresses is therefore questionable in species where failure to re-emerge has not been confirmed.
3. In this study, the alternative approach of microsatellite markers was used to reconstruct the within-fig breeding structure of a pollinating fig wasp by genetic analysis of the offspring. Broods of Liporrhopalum tentacularis , a species where foundresses regularly re-emerge from figs, were collected from figs of Ficus montana in their natural habitat in Indonesia as well as from an experimental glasshouse population in Leeds (U.K.).
4. The estimated foundress densities in the glasshouse population were similar to those in the field and ranged from one to six foundresses per brood.
5. Nearly 40% of all broods were produced by a single foundress, indicating that mating in these broods occurs exclusively between full siblings. High levels of inbreeding are therefore common in this species.     

Development and characterization of nine new microsatellite markers in Taraxacum (Asteraceae)

This study aims at developing and characterizing new microsatellite primer pairs in Taraxacum officinale auct. to produce polymorphic markers for genetical and evolutionary studies on apomixis in this sexual‐apomictic complex. A total of 24 diploid plants were tested for allelic polymorphism and heterozygosity. Out of nine loci three deviated significantly from the Hardy–Weinberg equilibrium expectations, probably due to the presence of null‐alleles. Successful cross‐species amplification was obtained for all markers in 29 Taraxacum microspecies from five sections.