José Francisco Pensiero

Phenotypic, molecular and symbiotic characterization of the rhizobial symbionts of Desmanthus paspalaceus (Lindm.) Burkart that grow in the province of Santa Fe, Argentina.

Desmanthus paspalaceus (Lindm.) Burkart belongs to the D. virgatus complex, subfamily Mimosoidae. The known potential as livestock fodder of several of these legumes prompted us to undertake a phenotypic, molecular, and symbiotic characterization of the D. paspalaceus symbionts in the Santa Fe province, Argentina. The rhizobia collected—containing isolates with different abiotic-stress tolerances—showed a remarkable genetic diversity by PCR fingerprinting, with 11 different amplification profiles present among 20 isolates. In selected isolates 16S-rDNA sequencing detected mesorhizobia (60%) and rhizobia (40%) within the collection, in contrast to the genus of the original inoculant strain CB3126—previously isolated from Leucaena leucocephala—that we typified here through its 16S rDNA as Sinorhizobium terangae. The results revealed the establishment by diverse bacterial genera -rhizobia, sinorhizobia, and mesorhizobia- of full N2-fixing symbiotic associations with D. paspalaceus. This diversity was paralleled by the presence of at least two different nodC allelic variants. The identical nodC alleles of the Mesorhizobia sp. 10.L.4.2 and 10.L.5.3 notably failed to group within any of the currently described rhizo-/brady-/azorhizobial nodC clades. Interestingly, the nodC from S. terangae CB3126 clustered close to homologs from common bean nodulating rhizobia, but not with the nodC from S. terangae WSM1721 that nodulates Acacia. No previous data were available on nod-gene phylogeny for Desmanthus symbionts. A field assay indicated that inoculation of D. paspalaceus with the local Rhizobium sp. 10L.11.4 produced higher aerial-plant dry weights compared to S. teranga CB3126–inoculated plants. Neither the mesorhizobia 10.L.4.2 or 10.L.5.3 nor the rhizobium 10L.11.4 induced root nodules in L. leucocephala or P. vulgaris. The results show that some of the local isolates have remarkable tolerances to several abiotic stresses including acidity, salt, and temperature; while exhibiting prominent N2 fixation; thus indicating suitability as candidates for inoculation of D. paspalaceus.

Evaluation and improvement of the ecogeographical representativeness of a collection of the genus Trichloris in Argentina

In Argentina, species of the genus Trichloris represent an important native forage resource adapted to drought and salinity. The capture and identification of adaptive traits associated with such conditions require long-term collection and characterization efforts. Ecogeographical land characterization (ELC) maps constitute an easy and useful tool to evaluate ecogeographical representativeness in established collections, allowing for the design of new collecting strategies. In the present study, an ELC map was generated from ecogeographical variables closely associated with the adaptation of the target species. For each ELC map category, the accessions preserved at the Trichloris genebank of the Facultad de Ciencias Agrarias-Universidad Nacional del Litoral were compared with external presence data. After the identification of the ecogeographical gap, a collecting expedition was designed. Collecting indices showed a significant improvement in the ecogeographical representativeness of the collection to the extent that accessions had a high probability of containing abiotic adaptation genes. The results emphasize the usefulness of ELC maps and the importance of planning collections through ecogeographical approaches.

Embryological studies on Trichloris (Poaceae, Chloridoideae)

Geraldina Alicia RICHARD*, María Carolina CERINO, Beatriz Gloria GALATI, Eliana De Luján EXNER, José Francisco PENSIERO Department of Plant Biology, Faculty of Agricultural Sciences, National University of the Littoral (Universidad Nacional del Litoral, in Spanish), Esperanza, Argentina National Council of Scientific and Technical Research, Buenos Aires, Argentina Department of Natural Resources and Environment, Faculty of Agriculture, National University of Buenos Aires (Universidad Nacional de Buenos Aires, in Spanish), Buenos Aires, Argentina

Genetic and environmental variation of seed weight in Trichloris species (Chloridoideae, Poaceae) and its association with seedling stress tolerance

ABSTRACT Background: Seed weight is a key fitness-related trait associated with plant adaptation and is commonly targeted in plant breeding. Aims: We evaluated seed weight variation within and between Trichloris crinita and Trichloris pluriflora across their geographical ranges in Argentina. Methods: Genetic variation in seed weight was evaluated through a common garden experiment. To examine the possible role of such variation in local adaptation, we compared the seed weight of plants of populations raised in the common garden with seed weight variation and ecogeographical variables across their original habitats. We also evaluated experimentally the effects of seed weight variation upon osmotic stress tolerance at germination. Results: Variation in seed weight existed in both species. Such variation had a genetic basis in T. crinita related to several ecogeographical variables. Larger seeds of T. crinita were associated with more stressful environments and produced larger seedlings under both osmotic stress and non-stress conditions. Conclusions: Our results suggest that seed weight variation in T. crinita is likely adaptive, with large seed having an advantage during early developmental stages, particularly under stressful conditions. Such knowledge should prove helpful in selecting the most suitable populations for restoration and plant breeding.

Functional dioecy in Gleditsia amorphoides (Fabaceae)

The genus Gleditsia (Fabaceae) comprises woody shrubs and trees that grow in temperate and subtropical regions around the world. This genus is characterised by sexual polymorphism and functionally unisexual flowers. Gleditsia amorphoides is the southernmost species of the genus, and is widely used as a source of timber and derived products for industrial applications (galactomannans are extracted from its seeds and saponins are derived from its fruits). The species is endemic to the Chaquenean Forest of South America. It is described as morphologically androdioecious, with male and perfect flowers appearing on different plants. In the current study, we characterised floral morphology, experimentally tested the breeding system and analysed flower visitors. Results indicated that G. amorphoides staminate flowers produce viable pollen grains and that perfect flowers have a functional gynoecium and empty anthers, where pollen abortion occurs early in floral development. The species relies on outcrossing, which depends mainly on pollen carried by insect pollinators, to produce seeds and fruits. We conclude that G. amorphoides is functionally dioecious, with staminate and pistillate floral morphs.

Nitrogen-fixing rhizobial strains isolated from Desmodium incanum DC in Argentina: Phylogeny, biodiversity and symbiotic ability

Desmodium spp. are leguminous plants belonging to the tribe Desmodieae of the subfamily Papilionoideae. They are widely distributed in temperated and subtropical regions and are used as forage plants, for biological control, and in traditional folk medicine. The genus includes pioneer species that resist the xerothermic environment and grow in arid, barren sites. Desmodium species that form nitrogen-fixing symbiosis with rhizobia play an important role in sustainable agriculture. In Argentina, 23 native species of this genus have been found, including Desmodium incanum. In this study, a total of 64 D. incanum-nodulating rhizobia were obtained from root nodules of four Argentinean plant populations. Rhizobia showed different abiotic-stress tolerances and a remarkable genetic diversity using PCR fingerprinting, with more than 30 different amplification profiles. None of the isolates were found at more than one site, thus indicating a high level of rhizobial diversity associated with D. incanum in Argentinean soils. In selected isolates, 16S rDNA sequencing and whole-cell extract MALDI TOF analysis revealed the presence of isolates related to Bradyrhizobium elkanii, Bradyrhizobium japonicum, Bradyrhizobium yuanmingense, Bradyrhizobium liaoningense, Bradyrhizobium denitrificans and Rhizobium tropici species. In addition, the nodC gene studied in the selected isolates showed different allelic variants. Isolates were phenotypically characterized by assaying their growth under different abiotic stresses. Some of the local isolates were remarkably tolerant to high temperatures, extreme pH and salinity, which are all stressors commonly found in Argentinean soils. One of the isolates showed high tolerance to temperature and extreme pH, and produced higher aerial plant dry weights compared to other inoculated treatments. These results indicated that local isolates could be efficiently used for D. incanum inoculation.

Seed dormancy and germination in different populations of the Argentinan endemic halophyte grass, Sporobolus phleoides (Poaceae: Chloridoideae)

Sporobolus phleoides Hack. is an endemic grass of Argentina that is considered an important genetic resource for saline environments. Knowledge of its germination behaviour is an indispensable requirement for the future potential use of this species. Thus, the effects of different factors on germination were evaluated in six representative populations collected from plants cultivated in a uniform environment. In addition, we investigated how the different parts of the seed contributed to dormancy and intraspecific variability. S. phleoides has non-deep physiological dormancy that appeared to be related to its testa. Thereby, dormancy was completely removed with puncturing treatments. High levels of germination were also obtained in seeds stratified at 8°C over 100 days in a solution of nitrates. After-ripening treatment did not have a significant effect in breaking dormancy. Similar germination behaviour and dormancy levels were observed in the different populations, especially when they were subjected to cold stratification. Although further work is needed, cold stratification appears to be the major factor in determining the time of seedling establishment in natural environments for this species.