Roger Kalla

Breeding Forage Plants in the Genome Era

Forage plant breeding has been largely based on phenotypic selection following sexual recombination of natural genetic variation found between and within ecotypes. Advances in plant genetic manipulation over the last 15 years have provided convincing evidence that these powerful technologies can complement and enhance plant breeding programs. Significant progress in the establishment of the methodologies required for the molecular breeding of forage plants has been made. Examples of current products and approaches for the application of these methodologies to forage grass and legume improvement are outlined. Large-scale genomic analysis of many organisms is under way with human, arabidopsis and rice genome sequences almost completed. Forage plant breeding is just now entering the genome era. The plethora of new technologies and tools now available for high-throughput gene discovery and genome-wide gene expression analysis have opened up opportunities for innovative applications in the identification, functional characterisation and use of genes of value in forage production systems and beyond. Examples of these opportunities, such as ‘molecular phenotyping’, ‘symbio-genomics’ and ‘xeno-genomics’ are introduced.

Molecular breeding of transgenic white clover (Trifolium repens L.) with field resistance to Alfalfa mosaic virus through the expression of its coat protein gene

Viral diseases, such as Alfalfa mosaic virus (AMV), cause significant reductions in the productivity and vegetative persistence of white clover plants in the field. Transgenic white clover plants ectopically expressing the viral coat protein gene encoded by the sub-genomic RNA4 of AMV were generated. Lines carrying a single copy of the transgene were analysed at the molecular, biochemical and phenotypic level under glasshouse and field conditions. Field resistance to AMV infection, as well as mitotic and meiotic stability of the transgene, were confirmed by phenotypic evaluation of the transgenic plants at two sites within Australia. The T0 and T1 generations of transgenic plants showed immunity to infection by AMV under glasshouse and field conditions, while the T4 generation in an agronomically elite ‘Grasslands Sustain’ genetic background, showed a very high level of resistance to AMV in the field. An extensive biochemical study of the T4 generation of transgenic plants, aiming to evaluate the level and composition of natural toxicants and key nutritional parameters, showed that the composition of the transgenic plants was within the range of variation seen in non-transgenic populations.

Molecular Breeding of Forage Legumes for Virus Resistance

Viruses such as alfalfa mosaic alfamovirus (AMV), white clover mosaic potex virus (WCMV) and clover yellow vein potyvirus (CYVV), which are members of the three largest groups of plant viruses, have been found to have significant adverse effects on forage legumes. Each of these viruses individually infects a large number of plant species, has a worldwide distribution, and causes significant losses, especially in pasture and grain legumes.

Field Evaluation of Transgenic White Clover with AMV Immunity and Development of Elite Transgenic Germplasm

Viral diseases such as alfalfa mosaic virus (AMV) cause significant reductions in dry matter yield and persistency of white clover (Trifolium repens L.). Transgenic white clover plants expressing the AMV coat protein (AMV-CP) gene and showing immunity to AMV infection were evaluated in multi-site small-scale field releases. Two transformation events showing field immunity to aphid-mediated AMV infection This article outlines the development of transgenic elite white clover germplasm with AMV immunity, involving the world’s first breeding nursery for transgenic white clover.were selected for elite transgenic germplasm development. Following top crosses with elite parental breeding lines, diallel crosses of heterozygous offspring plants and identification of AMV-CP homozygous T2 lines through quantitative PCR-based high-throughput screening, a breeding nursery with 1,300 transgenic white clover plants was established. Agronomically superior transgenic white clover plants were selected as parents for the production of world’s first AMV immune transgenic white clover cultivars.

Transgenesis and Genomics in Molecular Breeding of Temperate Pasture Grasses and Legumes

Significant advances in the establishment of the methodologies required for the molecular breeding of temperate forage grasses (Lolium and Festuca species) and legumes (Trifolium and Medicago species) are reviewed. Examples of current products and approaches for the application of these methodologies to forage grass and legume improvement are outlined. The plethora of new technologies and tools now available for high-throughput gene discovery and genome-wide expression analysis have opened up opportunities for innovative applications in the identification, functional characterisation and use of genes of value in forage production systems and beyond. Selected examples of our current work in pasture plant genomics, xenogenomics, symbiogenomics and microarray-based molecular phenotyping are discussed.