Warm-Season (C4) Turfgrass Genotypes Resistant to Spittlebugs (Hemiptera: Cercopidae).

Screening for resistance to insect pests is one of the early stages of grass breeding programs. Pasture spittlebugs are sap-sucking insects that potentially cause severe damage to turfgrasses, including the loss of functional quality and perenniallity. The Brazilian flora has a large number of grass species with wide morphological variability and adaptability to different soil and climate conditions that can potentially be used as lawns. However, no study has screened turfgrass genotypes for resistance to spittlebug attack. In this study, we evaluated the intra- and interspecific variability of 35 turfgrass genotypes in the genera Paspalum, Axonopus, and Zoysia for resistance to the pasture spittlebugs, Deois flavopicta (Stal) and Notozulia entreriana (Berg) (Hemiptera: Cercopidae), as measured by damage scores, densities of nymphs and adults, and level of antibiosis resistance. Genotypes were grouped into three groups using cluster analysis and principal component analysis: GroupI had genotypes associated with low damage scores and high density of adult spittlebugs; GroupII had genotypes with intermediate damage scores and low density of nymphs and adults; and GroupIII was formed by genotypes with high damage scores and high nymph density. Intra- and interspecific genotypic variability was related to antibiosis resistance and morphological variation among genotypes with some indicating nonpreference resistance and others indicating tolerance resistance. Our results indicate that besides antibiosis resistance studies, it is essential to evaluate the morphological variability of grass genotypes when screening for resistance to insects. Further studies are needed to elucidate the intraspecific variability of Paspalum notatum Flüggé genotypes for resistance to spittlebug attack.

Frequências de cortes em nove leguminosas forrageiras tropicais herbáceas cultivadas ao sol e sob plantação florestal / Cutting frequencies of nine herbaceous tropical forage legumes cultivated under full sun light and under a forest plantation

O objetivo deste trabalho foi estudar a produção e o valor nutritivo de nove espécies de leguminosas forrageiras herbáceas tropicais, cultivadas sob dois níveis de irradiação luminosa e seis frequências de corte na estação chuvosa, em Anhembi (SP), Brasil. Parcelas puras foram estabelecidas ao sol e sob plantação de Eucalyptus grandis, com 8 anos de idade, com 1.000 árvores/ha, que interceptou mais de 80% da radiação luminosa incidente. Avaliou-se a taxa de acúmulo de matéria seca, a proteína bruta e a digestibilidade in vitro da matéria seca em amostras de plantas colhidas em intervalos de 30, 60, 90 e 180 dias, com cortes adicionais aos 120 e 150 dias. Sob pleno sol, as leguminosas testadas toleraram cortes mais frequentes (intervalos de 30 - 90 dias), exceto o Lablab. Na sombra, o grau de tolerância variou conforme a espécie; em termos de produção de MS e de persistência, a Centrosema e a Puerária se destacaram dentre as demais leguminosas comparadas, quando os cortes foram realizados em intervalos de 60 dias, enquanto o Arachis e o Estilosantes foram os mais produtivos quando os cortes ocorreram em intervalos de 120 dias, mantendo o valor nutricional. O Alysicarpus e a Aeschynomene não persistiram sob o nível de sombreamento que prevaleceu nesse experimento.

The aim of this study was to evaluate the production and nutritive value of nine tropical legumes under two light intensities and six cutting regimens in the wet season, in Anhembi (SP) - Brazil. Pure stands were established in full light and under an eight-year-old eucalyptus plantation with 1.000 plants per hectare. The trees intercepted over80% of the incident radiation. Dry matter herbage accumulation, dry matter in vitro digestibility and crude protein under the cutting intervals 30, 60, 90 and 180 days, with additional cuttings at 120 and 150 days were evaluated. With the exception of Lablab, all other tested legume species tolerated higher cutting frequency under when grown under full sun light then under shade. The degree of shade-tolerance varied according to the species; Centrosema and Pueraria produced well at cutting intervals of 60 days, showing higher dry matter production and persistence while Arachis and Stylosanthes showed better results under longer cutting intervals, keeping the nutritional value, and can be indicated for differential grazing. Alysicarpus and Aeschynomene did not persist under the prevailing conditions.

Complete asynapsis resulting in 2n pollen formation in Paspalum jesuiticum Parodi (Poaceae).

Cytological investigation revealed complete asynapsis during microsporogenesis in 2 wild accessions of Paspalum jesuiticum collected in distinct Brazilian regions. Both accessions were hexaploid (2n = 6x = 60) and 60 univalents could be counted at diakinesis. In this phase, the majority of meiocytes exhibited univalents with both chromatids. After alignment at the metaphase plate, the chromatids segregated to the poles. Only 1 meiotic division (equational) occurred, and after cytokinesis, a dyad with 2n microspores was formed. The genetic constitution of the 2n gametes was equivalent to that of first division restitution (FDR). Since recombination did not occur, 100% transmission of parental heterozygosity could be expected from the FDR 2n gametes. The meiotic behavior of both accessions suggested that they resulted from a recent natural hybridization event. The potential use of the 2n gametes in Paspalum breeding programs has been discussed.

Microsporogenesis in Paspalum conspersum Schrad. (Virgata group) with different ploidy levels.

Knowledge about the cytology and reproductive behavior of a species is indispensable for hybridization programs. This is especially true for species belonging to the genus Paspalum, among which apomixis and a wide range of ploidy levels are frequently found. Paspalum conspersum Schrad. is a robust and warm-season perennial bunchgrass native to South America. Previous studies have indicated that both tetraploid and hexaploid races exist in this species; however, only information related to tetraploids has been applied to another taxon. In this study, a cytological investigation in two Brazilian accessions collected in different regions revealed tetraploidy in the accession BRA-012823 (2n = 4x = 40), with chromosome pairing in bivalents and normal meiosis and tetrad formation, and pentaploidy (2n = 5x = 50) in the accession BRA-022748, which presented total asynapsis. In this latter accession, 50 univalents could be scored at diakinesis. After alignment at the metaphase plate, sister chromatids segregated to the poles. Only one meiotic division (equational) occurred, and after cytokinesis, 100% of the dyads that formed had 2n microspores. The meiotic behavior during microsporogenesis, which showed 10 delayed univalents to reach the metaphase plate, suggests that this accession is a recent natural hybrid constituted by a parental genome with 40 chromosomes and another with 10 chromosomes. The potential usage of these accessions in Paspalum breeding has been discussed.

Microsatellite loci for Paspalum atratum (Poaceae) and cross-amplification in other species.

PREMISE OF THE STUDY: Paspalum atratum is a perennial, cespitose, tropical grass native to Central and South America. This species belongs to a polyploid complex (Plicatula group) little known at the genetic level. The characterized microsatellite markers provide new informative tools for further studies of the hybridization, mating systems, and structure of the population. • METHODS AND RESULTS: Using the microsatellite-enriched library method, we isolated and characterized 19 microsatellite markers from P. atratum. Eleven of them were polymorphic, showing a variable degree of variation, while eight were monomorphic in the samples analyzed. Additionally, the transferability of these microsatellite markers was tested in other species. • CONCLUSIONS: These results suggest that the characterized markers have enough discriminatory potential to be used in genetic characterizations of Paspalum taxa, which are based on an understanding of their mating systems and genetic structure, as well as in understanding the evolutionary processes involved in the evolution of groups of Paspalum.