Random generation and selection of one- and two-dimensional designs for experiments on blocks of natural size

Many incomplete block design strategies have been devised to improve the efficiency of experiments. However, the constraints imposed by these designs can be unrealistic because natural blocks may not be all the same size or there may be no conventional designs for required treatment, replication, block and plot combinations. In addition, because of similar constraints, two-dimensional block designs—the so called row-column designs— are used less frequently than the occurrence of conditions where their use would result in greater experimental efficiency. This article explores the properties of an easy to use random generation and selection strategy for obtaining block and row-column designs. Although the strategy does not necessarily obtain the best possible designs when judged by any one of the many criteria, this apparent disad vantage is outweighed by the generality and ease of use. It is concluded that present-day model fitting methods remove the constraints which have been traditionally imposed on designs and the benefits of using block designs can be extended by the use of informal design methods.     

High-throughput phenotyping of lateral expansion and regrowth of spaced <Emphasis Type="Italic">Lolium perenne</Emphasis> plants using on-field image analysis

Background

Genetic studies and breeding of agricultural crops frequently involve phenotypic characterization of large collections of genotypes grown in field conditions. These evaluations are typically based on visual observations and manual (destructive) measurements. Robust image capture and analysis procedures that allow phenotyping large collections of genotypes in time series during developmental phases represent a clear advantage as they allow non-destructive monitoring of plant growth and performance. A L. perenne germplasm panel including wild accessions, breeding material and commercial varieties has been used to develop a low-cost, high-throughput phenotyping tool for determining plant growth based on images of individual plants during two consecutive growing seasons. Further we have determined the correlation between image analysis-based estimates of the plant’s base area and the capacity to regrow after cutting, with manual counts of tiller number and measurements of leaf growth 2 weeks after cutting, respectively. When working with field-grown plants, image acquisition and image segmentation are particularly challenging as outdoor light conditions vary throughout the day and the season, and variable soil colours hamper the delineation of the object of interest in the image. Therefore we have used several segmentation methods including colour-, texture- and edge-based approaches, and factors derived after a fast Fourier transformation. The performance of the procedure developed has been analysed in terms of effectiveness across different environmental conditions and time points in the season.

Results

The procedure developed was able to analyse correctly 77.2 % of the 24,048 top view images processed. High correlations were found between plant’s base area (image analysis-based) and tiller number (manual measurement) and between regrowth after cutting (image analysis-based) and leaf growth 2 weeks after cutting (manual measurement), with r values up to 0.792 and 0.824, respectively. Nevertheless, these relations depend on the origin of the plant material (forage breeding lines, current forage varieties, current turf varieties, and wild accessions) and the period in the season.

Conclusions

The image-derived parameters presented here deliver reliable, objective data, complementary to the breeders’ scores, and are useful for genetic studies. Furthermore, large variation was shown among genotypes for the parameters investigated.

     

Inducer line generated double haploid seeds for combined waxy and opaque 2 grain quality in subtropical maize (<Emphasis Type="Italic">Zea mays.</Emphasis> L.)

The implementation of modern inducer lines in maize breeding can substantially decrease the time required to create elite inbred lines. In industrialized countries, this method has already largely replaced conventional backcross methods. However, the application of in vivo gynogenesis for inducing doubled haploids is still limited to European and US maize germplasms and has still to be adapted for exotic plant material. The reliability of three modern European inducer lines from the University of Hohenheim (Germany) was investigated for the production of haploid progenies from subtropical specialty maize. Three Chinese hybrids heterozygous for waxy maize and opaque 2 were used as maternal donor material, as maize double recessive for waxy and opaque 2 may improve the nutrition of ethnic minorities in Southeast Asia. However, many false positives were detected by flow cytometry among putative haploid seeds based on anthocyanin pigmentation because the color expression was inhibited in almost 50% of the induced seeds from this maternal plant material. Based on flow cytometry, the haploid induction rates were high with 10.2–12.3%, and the chromosome doubling rates were around 50%; therefore the principal potential of producing DH was confirmed for subtropical maize. However inducer lines for the precise and fast recognition of truly induced haploid seeds still need to be developed.