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Biomass production represents a fundamental biological process of both ecological and agricultural significance. The genetic basis of biomass production is unknown but asssumed to be complex. We developed a full sib, [F.sub.1] mapping population of autotetraploid Medicago sativa (alfalfa) derived from an intersubspecific cross that was known to produce heterosis for biomass production. We evaluated the population for biomass production over several years at three locations (Ames, IA, Nashua, IA, and Ithaca, NY) and concurrently developed a genetic linkage map using restriction fragment length polymorphism (RFLP) and simple sequence repeat (SSR) molecular markers. Transgressive segregants, many of which exhibited high levels of heterosis, were identified in each environment. Despite the complexities of mapping within autotetraploid populations, single-marker analysis of vailance identified 41 marker alleles, many on linkage groups 5 and 7, associated with biomass production in at least one of the sampling periods. Seven alleles were associated with biomass production in more than one of the sampling periods. Favorable alleles were contributed by both parents, one of which is from the M. sativa subsp. falcata germplasm. Thus, increased biomass production alleles can be gleaned from unadapted germplasm. Further, the positive quantitative trait locus (QTL) alleles from the parents are partially complementary, suggesting these loci may play a role in biomass production heterosis.

ABSTRACT Although phenotypic correlations generally show winter hardiness and late summer and autumn growth (fall dormancy, FD) in alfalfa (Medicago sativa L.) to be strongly associated (r = 0.90), the [...]

Determining the ploidy of germplasm is necessary before initiating breeding or genetic studies. This study was conducted to determine the ploidy of 263 accessions of Medicago sativa subsp, falcata Arcengeli and 20 accessions of M. sativa subsp, sativa (L.) L. & L acquired from the USDA National Plant Germplasm System (NPGS). Ploidy was assessed using both flow cytometry and root tip chromosome counts. Approximately 68% of the subsp, falcata accessions were tetraploid and 32% were diploid. In all cases where ploidy determinations by root tip chromosome counting and flow cytometry differed, reanalysis of root tips from a new set of plants indicated the first counts were incorrect. The distribution of the accessions indicated that few diploids are available through the NPGS from the eastern range of the species distribution (Kazahkstan, Mongolia, China, and eastern Russia). Flower color variants were identified in many subsp. falcata accessions. Three of 20 subsp, sativa accessions were diploid, indicating they should be reclassified as M. sativa subsp, coerulea Schmalh. Flow cytometry allowed faster and more accurate ploidy determination than root tip chromosome counting. Ploidy determination will allow researchers to more accurately identify and request germplasm suited to their project., ALFALFA, Medicago sativa L., breeding programs in the United States have concentrated predominantly on M. sativa subsp, sativa germplasm. M. sativa subsp, falcata, which has good winter-, grazing-, and drought-tolerance [...]

Plant organs, such as seeds, are primary sources of food for both humans and animals. Seed size is one of the major agronomic traits that have been selected in crop plants during their domestication. Legume seeds are a major source of dietary proteins and oils. Here, we report a conserved role for the BIG SEEDS1 (BS1)geneinthe control of seed size and weight in the model legume Medicago truncatula and the grain legume soybean (Glycine max). BS1 encodes a plant-specific transcription regulator and plays a key role in the control of the size of plant organs, including seeds, seed pods, and leaves, through a regulatory module that targets primary cell pro- liferation. Importantly, down-regulation of BS1 orthologs in soybean by an artificial microRNA significantly increased soybean seed size, weight, and amino acid content. Our results provide a strategy for the increase in yield and seed quality in legumes. [ABSTRACT FROM AUTHOR]

Insertional mutagenesis is a cornerstone of functional genomics. High-copy transposable element systems such as Mutator ( Mu) in maize ( Zea mays) afford the advantage of high forward mutation rates but pose a challenge for identifying the particular element responsible for a given mutation. Several large mutant collections have been generated in Mu-active genetic stocks, but current methods limit the ability to rapidly identify the causal Mu insertions. Here we present a method to rapidly assay Mu insertions that are genetically linked to a mutation of interest. The method combines elements of MuTAIL (thermal asymmetrically interlaced) and amplification of insertion mutagenized sites (AIMS) protocols and is applicable to the analysis of single mutants or to high-throughput analyses of mutant collections. Briefly, genomic DNA is digested with a restriction enzyme and adapters are ligated. Polymerase chain reaction is performed with TAIL cycling parameters, using a fluorescently labeled Mu primer, which results in the preferential amplification and labeling of Mu-containing genomic fragments. Products from a segregating line are analyzed on a capillary sequencer. To recover a fragment of interest, PCR products are cloned and sequenced. Sequences with lengths matching the size of a band that co-segregates with the mutant phenotype represent candidate linked insertion sites, which are then confirmed by PCR. We demonstrate the utility of the method by identifying Mu insertion sites linked to seed-lethal mutations with a preliminary success rate of nearly 50%. [ABSTRACT FROM AUTHOR]

In this chapter we describe an Agrobacterium tumefaciens transformation method of soybean that utilizes mature half seeds and regeneration from the cotyledonary node region. This method results in fertile transformed soybean plants and transgenic seed in approximately 9 months. Using mature half seeds as starting material has proven to be a reliable method that does not require additional wounding for infection to occur. We have continued to make improvements in the protocol, resulting in an efficient plant regeneration system.