Resistência à mancha preta e qualidade agronômica de plantas rc1f2 de cruzamentos do híbrido anfidiplóide (Arachis ipaensis x A. duranensis) com o amendoim cultivado (A. hypogaea) / Resistance to late leafspot and agronomic quality of bc1f2 plants from crosses between the amphyploids hibrid (arachis ipaensis x a. duranensis) and the cultivated peanut (a. hypogaea)

A resistência à mancha preta (Cercosporidium personatum) e a condição agronômica de plantas de amendoim foram avaliadas em populações RC1F2 obtidas de cruzamentos do anfidiplóide (Arachis ipaensis x Arachis duranensis) com o genitor recorrente, cultivar Runner IAC 886. O experimento foi conduzido em condições de campo, em Pindorama, SP., sob condições naturais de ocorrência da doença. A doença foi avaliada em cada planta, em duas épocas, usando uma escala de notas visuais de 1 a 9, considerando o número de lesões nas folhas e a desfolha causada pela doença. Foi realizada após a colheita, em 90 plantas tomadas ao acaso, a avaliação da produção de vagens e grãos/planta, o rendimento de grãos após descascamento, massa média de grãos, número de vagens/planta, número e porcentagem de vagens com dois grãos. Os resultados mostraram ampla variabilidade para resistência à doença. Dependendo do genitor hypogaea utilizado nos cruzamentos iniciais com o anfidiplóide, 4,2 a 7,7% de plantas portadoras de resistência próxima a do parental silvestre resistente (A. ipaensis) foram resgatadas em F2. Observaram-se diferenças significativas entre plantas RC1F2 em função da planta F1 da qual descendem, tanto para resistência à doença como para caracteres agronômicos, tendo em vista a condição segregante das plantas F4 utilizadas nos cruzamentos com o genitor recorrente, cultivar Runner IAC 886. As correlações negativas observadas entre resistência à doença e caracteres agronômicos como produção de vagens e grãos/planta e massa média de grãos sugerem a necessidade de novo ciclo de retrocruzamentos para quebrar eventuais ligações indesejáveis e gerar indivíduos resistentes mais próximos do padrão comercial.

Resistance to late leafspot (Cercosporidium personatum) and agronomic condition of peanut plants were assessed in segregating RC1F2 populations obtained from crosses between the amphidiploid (A. ipaensis x A. duranensis) and the recurrent parent, cultivar Runner IAC 886. The experiment was carried out at Pindorama, SP, under natural field conditions of the disease. Disease was evaluated at two dates during the growing cycle, in 1,500 plants, using a scale of visual notes ranging from 1 to 9, and taking into consideration the number of lesions in leaves and the degree of defoliation caused by the disease. The data obtained were used to estimate the AUDPC (Area Under the Disease Progress Curve). Agronomic evaluations were performed after harvesting, in 90 randomly taken plants. The following agronomic characters were evaluated: pod and kernel production per plant, shelling percentage, number of pods per plant, number and percentage of two-seed pods. The results showed wide variability for resistance to the disease. Depending on the hypogaea parent used in the initial crosses with the amphidiploids, 4,2 to 7,7% of plants with disease resistance close to the wild resistant parent (A. ipaensis) could be rescued in the F2 generation. Significant differences were observed between RC1F2 plants descendent from the same F1 plant, in either disease resistance or in agronomic traits, due to the segregant condition of the F4 plants used in the crosses to the recurrent parent, cultivar Runner IAC 886. Some of the RC1F1:2 plant families exhibited agronomic condition close to the cultivar IAC Caiapó, especially in production of pods and kernels, shelling percentage and average kernel weight. However, the large majority of the segregants in this generation still showed high percentages of one-seed pods. This condition, and the negative correlations observed between resistance to the disease and agronomic traits such as pod and kernel production per plant and average kernel weight suggest that a new backcrossing cycle is needed to break eventual undesirable linkages and generate resistant individuals closer to the commercial standards.

The synthesis of a new cassava-derived species, Manihot vieiri Nassar

A new species was synthesized artificially by chromosome doubling in a hybrid. The ensuing polyploid type exhibits an apomictic nature and maintains its morphological characteristics in the progeny. It showed a frequency of multiembryonic sacs of 29% in the ovules examined, whereas sacs were absent in the diploid type.