Rafael Reyno

Genetic diversity and DNA content of three South American and three Eurasiatic Trifolium species

Six species of Trifolium (T. polymorphum Poir., T. riograndense Burkart, T. argentinense Speg., T. medium L., T. pratense L. and T. repens L.) were analyzed using inter-simple sequence repeats (ISSR) markers. Six selected primers generated 186 polymerase chain reaction (PCR) products exploring 112 loci in 34 genotypes analyzed with molecular sizes ranging from 200 to 1300 bp. These primers were able to discriminate among and within species, with the PCR products being on average 41.6% species-specific and 59.9% polymorphic at the within species level. Nuclear DNA content was determined by flow cytometry and revealed variation among species. The 1Cx genome size values were calculated and were found to range from 0.46 pg (T. pratense) to 0.96 pg (T. polymorphum). Genome size values of South American species were higher than those of Eurasiatic origin. The analyses of the molecular data grouped the six species in agreement with their geographical origin and clearly differentiate T. polymorphum from T. argentinense. The Eurasiatic group showed the highest average of species-specific bands (45.3%) and the South American group exhibited the highest amount of total bands (59.7). The highest level of intra-species polymorphisms was detected in T. argentinense (92.9%), followed by T. medium (89.5%).

QTL Mapping of Aluminum Tolerance in Tetraploid Alfalfa

Aluminum (Al) toxicity in acid soils is one of the factors limiting crop production. Alfalfa (Medicago sativa L.) is one of the most important forage legumes worldwide and is susceptible to Al toxicity. Al tolerance in alfalfa was identified in a diploid Medicago sativa subs. caerulea accession (Sledge et al., 2002) and has been successfully integrated at the tetraploid level in the Al-tolerant genotype Altet-4. The goals of this study are to identify and confirm quantitative trait loci (QTL) for Al-tolerance in tetraploid alfalfa. Two populations of at least 190 individuals each were developed from crosses between Altet-4 (Al-tolerant) and the Al-susceptible genotypes 95-608 derived from CUF-101, and NECS141, a semi-dormant breeding line developed in Iowa. The parental lines and the progeny from the mapping populations were screened using a callus bioassay and a whole plant assay. Genetic linkage maps constructed using EST-SSR markers (Sledge et al., 2005) were developed and used to identify QTL associated with Al tolerance. Comparison of QTL identified using different screening methods will be discussed. The long-term goal of this research is to use molecular markers associated with the Al-tolerance trait to accelerate the development of alfalfa cultivars with improved productivity in acidic and Al-toxic soils.

Seed softening patterns of forage legumes in a temperate/subtropical environment in Uruguay

Few studies have been conducted in annual and perennial forage legumes to investigate the development of hardseededness and the subsequent pattern of seed softening in temperate and subtropical regions of South America. Experiments were conducted during 2007 and 2008 in central Uruguay to follow the pattern of seed softening in 35 annual and perennial forage legumes, including three native species of Uruguay and five commercial cultivars. Newly ripened seeds of each plant material were placed in mesh packets on the soil surface in mid-summer. Samples were recovered monthly for germination tests and the proportion of residual hard seeds determined. The native species Adesmia bicolor (Poir.) DC., Adesmia securigerifoli a Herter, and Ornithopus micranthus (Benth.) Arechav., together with Ornithopus pinnatus (Mill.) Druce cv. INIA Molles behaved similarly. They showed high levels of initial hard seed from 78% in A. bicolor to 99% in A. securigerifolia and O. pinnatus cv. INIA Molles in 2007; displayed pulses of seed softening, particularly in autumn, and retained moderate levels of residual hard seed for the development of a soil seed bank ranging from 15% in A. bicolor to 49% in O. micranthus. These appear to be desirable characteristics for persistence of forage legumes in subtropical grasslands, both for annual and perennial species. Trifolium repens L. and Lotus corniculatus L. produced few hard seeds, only 2% and 13% respectively were hard after 1-mo in the field and were completely soft by July placing extra reliance on their vegetative propagation for persistence. Materials of L. arenarius Brot. showed pronounced late autumn softening, while materials of L. ornithopodioides L. showed extremely high levels of hardseededness (between 96% and 100%) and no softening during the evaluation period, apart from two materials that were completely soft seeded. Mediterranean forage legumes should be properly evaluated in temperate and subtropical regions as their seed softening behavior is likely to be substantially modified in these summer moist environments.