ABSTRACT The objective of this study was to evaluate 94 Paspalum notatum genotypes over two growing seasons to estimate genetic dissimilarity through agronomic traits and the distance between genotypes. This information is used to create an ideotype from the best averages obtained for the set of characteristics evaluated. Seven apomitic, three sexual, and 81 hybrid genotypes were compared with native genotypes “André da Rocha”, “Bagual”, and cultivar “Pensacola” as controls. There is genetic variability in P. notatum for the studied characteristics, and distinct genotypes with superior characteristics can be used in new combinations between apomictic and sexual plants to obtain hybrids. The characters with the greatest relative contribution to the dissimilarity between the genotypes were tiller density, stem dry mass, and leaf dry mass yield. Thus, these characteristics are suitable criteria to infer genetic distance studies in P. notatum . The selection index based on the ideotype is an auxiliary tool in the breeding process. The ideotype must be based on characteristics of interest according to the objective of the breeding program, as well as on the breeder’s prior knowledge in relation to culture.

RESUMO O gênero Paspalum compõe as pastagens naturais das regiões tropicais e subtropicais da América com várias espécies de reconhecido potencial forrageiro. O objetivo deste estudo foi avaliar a influência de diferentes níveis de fertilização nitrogenada sobre os caracteres agronômicos e na eficiência de utilização de nitrogênio por genótipos superiores de P. notatum Flügge. Foram avaliados quatro níveis de fertilização nitrogenada (0, 60, 180 e 360 kg N ha-1) e nove genótipos, seis provenientes do United States Departament of Agriculture (USDA) (30N, 36N, 48N, 70N, 83N e 95N), coletados na América do Sul, dois genótipos nativos do Rio Grande do Sul, Brasil (André da Rocha e Bagual) e a cv. Pensacola. O delineamento experimental utilizado foi o de blocos casualizados em esquema fatorial 4 x 9, com quatro repetições de campo. A partir da variabilidade de respostas encontradas para os caracteres agronômicos são indicados a prosseguir no programa de melhoramento genético os genótipos 48N, André da Rocha e Bagual por atingirem as máximas eficiências produtivas de acordo com as doses de N testadas.O genótipo 36N que obteve a maior eficiência de utilização de nitrogênio, demonstrando-se biologicamente viável com a menor dose de N, equivalente a 60 kg de N ha-1.

SUMMARY The Paspalum genus forms the natural pastures of the tropical and subtropical regions of America and includes several species of recognized forage potential. The aim of this study was to evaluate the influence of different levels of nitrogen fertilization on the agronomic traits and nitrogen use efficiency in superior genotypes of Paspalum notatum Flügge. Four nitrogen fertilization levels (0, 60, 180 and 360 kg N ha-1) and nine genotypes were evaluated, six from the United States Department of Agriculture (USDA) (30N, 36N, 48N, 70N, 83N and 95N), collected in South America, two native genotypes of Rio Grande do Sul, Brazil (André da Rocha and Bagual) and cv. Pensacola. The experimental design was a randomized complete block in a 4 x 9 factorial, with four field replications. From the variability of the responses found for the agronomic traits, the genotypes 48N, André da Rocha and Bagual are indicated to continue in the breeding program because they reach the maximum productive efficiencies according to the doses of N tested. The genotype 36N obtained the highest efficiency of nitrogen utilization, being biologically viable with the lowest N dose, equivalent of 60 kg of N ha-1.

RESUMO: O objetivo deste estudo foi avaliar a variabilidade de híbridos interespecíficos de Paspalum plicatulum x P. guenoarum por meio do desempenho agronômico e tolerância ao frio, bem como estimar as correlações fenotípicas de diferentes caracteres ligados à produção de forragem. Foram utilizados 20 híbridos, um acesso de P. guenoarum , um de P. plicatulum e a cultivar 'Pensacola' ( P. notatum ). As avaliações foram realizadas em plantas individuais, em delineamento completamente casualizado, com cinco repetições. Os genótipos de Paspalum apresentam variabilidade para massa seca total, massa seca de folhas e relação folha: colmo e na tolerância ao frio. É possível selecionar os híbridos 08Q01 e 08Q44 para novas etapas dentro de um programa de melhoramento de forrageiras. As estimativas de correlações fenotípicas podem auxiliar na seleção de genótipos com caracteres agronômicos superiores.

ABSTRACT: The goal of this study was to assess the variability of Paspalum plicatulum x P. guenoarum interspecific hybrids in terms of agronomic performance and their tolerance to cold conditions, as well as to estimate the correlation of different phenotypic characters associated with forage production. Twenty hybrids plants were used, besides one access P. guenoarum , one of P. plicatulum and the cultivar 'Pensacola' ( P. notatum ). Assessments were performed on individual plants, in a completely randomized design with five repetitions. Paspalum genotypes presented variability in total dry matter, leaf dry mass, leaf: stem ratio, and tolerance to cold. We suggest selection of the hybrids 08Q01 and 08Q44 for new stages within a forage improvement program. Estimates of phenotypic correlation may aid in the selection of genotypes with better agronomic traits.