4Bolsista CNPq. *Autor correspondente
O gênero Adesmia DC. possui várias espécies de leguminosas nativas do Sul do Brasil, algumas dessas apresentando um grande potencial forrageiro. Dentre os vários fatores a serem avaliados nessas espécies, está a tolerância ao alumínio, uma vez que grande parte dos solos dessa região são ácidos, possuindo altos teores desse elemento. Neste trabalho, uma população de A. latifolia e uma população de A. tristis foram submetidas a cinco doses de alumínio (0; 0,15; 0,45; 0,75 e 1,5mg l), em solução nutritiva contendo apenas cálcio (25mg l) e foram avaliadas quanto à massa e ao comprimento de raízes. Ao final de 13 dias de cultivo, foi observado que ambas as espécies sofreram inibição na emissão de raízes secundárias, sendo que A. tristis evidenciou sintomas de toxidez do alumínio, demonstrando engrossamento e tortuosidade da raiz principal em relação a A. latifolia. Houve efeito significativo para o fator espécie, para o comprimento e massa de raiz, e interação significativa de espécie-alumínio para a taxa de crescimento relativo da raiz (TCR), indicando resposta diferencial das duas espécies às doses de alumínio. A. latifolia não apresentou decréscimo significativo na TCR, sugerindo tolerância para as doses testadas, enquanto A. tristis foi sensível, diminuindo o alongamento radicular.
Trifolium polymorphum Poir. is an amphicarpic forage legume from southern Brazil, Uruguay, Argentina, Paraguay and Chile. Information on the genetic diversity of natural populations in natural grasslands in southern Brazil is limited. In order to increase the knowledge about this species, an analysis of the genetic diversity was carried out in 10 natural populations of T. polymorphum with the use of 20 microsatellite markers. The expected heterozygosity in T. polymorphum populations ranged from 0.40 to 0.43, with a mean of 0.42. A total of 193 alleles were detected with a mean of 9.3 alleles per locus and polymorphic information content (PIC) for these markers of 0.62 to 0.89 with a mean of 0.84.The grouping based on the Jaccard's coefficient of similarity classified populations, regardless of their regions of origin, into two groups with a mean similarity coefficient of 0.32, reflecting the high genetic variability of the populations, especially those located in the Campanha phytogeographic region. This information on diversity can be used to plan future germplasm collection strategies for conservation purposes and also for the breeding of the species.
Paspalum notatum Flüggé (bahiagrass) is the most important forage grass in the native grasslands of southern Brazil; the native germplasm is tetraploid and apomictic. Breeding to produce cultivars has been possible due to chromosome doubling of sexual diploid accessions, allowing hybridizations with apomictic genotypes, generating progenies with variability for agronomic traits and segregating for reproduction mode. The aim of this study was to determine the reproduction mode of selected hybrids derived from intraspecific crosses through cytoembryological analysis and to evaluate the level of apospory expressivity. Eighty one tetraploid hybrids corresponding to 21 families of sexual and apomictic parents were generated and 28 most productive plants based on their superior agronomic performance in the field were evaluated. Sixteen hybrids were reproduced sexually and 12 of them were highly apomictic or facultative apomictic. Sexual hybrids may be used for further crosses in the breeding program while highly apomictic plants produce uniform progeny and become candidates of new cultivars to promote pasture diversification.
BRSURS Entrevero" is a white clover cultivar, indicated for intercropping with winter grasses and for oversowing natural and subtropical pastures in areas with high fertility and humidity. It has high quality and forms a mat of stolons that covers completely the soil, with a prostrate habit with the growth buds close to the surface, resulting in a high grazing aptitude.
An interesting aspect of the biology of Trifolium polymorphum, an endemic species of the natural pastures of Rio Grande do Sul State in Brazil, is that it is amphicarpic. Amphicarpy is a fascinating reproductive strategy in which aerial and subterranean seeds are produced by the same plant. We evaluated the number, size and weight of aerial and subterranean seeds of two populations (Bagé and Santana do Livramento) of T. polymorphum which have grown from the regrowth of storage roots and in the absence of herbivory. Aerial flowers produced more seeds than subterranean flowers, about 14 times in the Santana do Livramento population and nine times in the Bagé population. However subterranean seeds were heavier than aerial seeds. We suggest that in the natural pastures of Rio Grande do Sul, where intense grazing and trampling can periodically destroy the aerial part of the plants, the occasional formation of subterranean seeds in T. polymorphum provides an alternative safety system in terms of population persistence. Although amphicarpic, T. polymorphum invests early in asexual reproduction through the production of storage roots, which favors the persistence in unfavorable habitats for sexual reproduction, and thus plants may persist vegetatively year after year without the need of regeneration by seeds.
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