Comportamento meiótico de híbridos interespecíficos entre tetraplóides artificiais de Brachiaria ruziziensis e tetraplóides apomíticos de B. brizantha (Poaceae)

O comportamento meiótico de quatro híbridos interespecíficos promissores de Brachiaria foi avaliado por metodologia citogenética convencional. Os genitores femininos eram dois acessos sexuais tetraploidizados artificialmente de B. ruziziensis (R41 e R44, 2n = 4χ = 36), os quais foram cruzados com um genσtipo tetraplσide natural apomítico agronomicamente superior de B. brizantha (B140 - BRA003395). Três deles (HBGC313, HBGC 315 e HBGC324) eram sexuais e um (HBGC325) apomítico. A análise de algumas células em diacinese revelou a presença de configurações cromossômicas multivalentes, sugerindo que recombinação genética e introgressão de alguns genes poderão estar presentes. Os quatro híbridos apresentaram freqüências e tipos variados de anormalidades meióticas. Anormalidades relacionadas à segregação irregular de cromossomos devido à poliploidia foram comuns entre os híbridos e caracterizadas pela presença de cromossomos em ascensão para os pólos e cromossomos retardatários, ambos levando à formação de micronúcleos em telófases e tétrades e, como conseqüência, gametas desbalanceados. Uma anormalidade genótipo-específica, relacionada à orientação do fuso (uma possível mutação fuso divergente) foi observada pela primeira vez em dois dos híbridos, HBGC313 e HBGC325. O híbrido sexual HBGC324 apresentou menor freqüência de anormalidades meióticas, podendo ser usado como genitor feminino em futuros cruzamentos no programa de melhoramento. A frequência e os tipos de anormalidades observadas podem afetar a fertilidade e a produção de sementes. Com base nos resultados, o híbrido HBGC324 é recomendado para o programa de melhoramento. Híbridos devem produzir grande quantidade de sementes viáveis, além de matéria seca com alto valor nutritivo para serem amplamente utilizados na produção de pastagens. Devido à pseudogamia, os híbridos apomíticos superiores necessitam de grãos de pólen viáveis para fertilizar o núcleo secundário do saco embrionário assegurando o desenvolvimento vigoroso do endosperma e a produção de sementes.The meiotic behavior of four interspecific promising hybrids was evaluated by conventional cytological methods. The female genitors were two artificially tetraploidized sexual accessions of B. ruziziensis (R41 and R44, 2n = 4χ = 36), which were crossed to an agronomically superior natural tetraploid apomictic genotype of B. brizantha (B140 - BRA003395). Three of them (HBGC313, HBGC 315, and HBGC324) were sexual and one (HBGC325) apomictic. Analyses of some cells in diakinesis revealed multivalent chromosome configurations, suggesting that genetic recombination and introgression of some genes could be present. The four hybrids had different types of meiotic abnormalities at various frequencies. Abnormalities related to irregular chromosome segregation due to polyploidy were common among these hybrids, and characterized by precocious chromosome migration to the poles, laggard chromosomes, both generating micronuclei in telophases and tetrads and, as a consequence, unbalanced gametes. One abnormality genotype-specific, related to spindle orientation (a putative divergent spindle mutation), was recorded for the first time in two of the hybrids, HBGC313 and HBGC325. The sexual hybrid HBGC324 had the lower rate of abnormalities, and it could be used as a female genitor in future crosses in the breeding program. The abnormalities present in these hybrids may impact fertility and affect seed production. Based on the results, HBGC324 is the single hybrid recommended to the breeding program. Hybrids must produce a good amount of viable seeds, besides good overall dry matter production and nutritive value, in order to be widely utilized and adopted in production systems. Due to pseudogamy, the desirable superior apomictic hybrids need viable pollen grains to fertilize the secondary nucleus of the embryo sac and thus ensure normal and vigorous endosperm development and plenty of seed set

Meiotic behavior of interspecific hybrids between artificially tetraploidized sexual Brachiaria ruziziensis and tetraploid apomictic B. brizantha (Poaceae)

The meiotic behavior of four interspecific promising hybrids was evaluated by conventional cytological methods. The female genitors were two artificially tetraploidized sexual accessions of B. ruziziensis (R41 and R44, 2n = 4χ = 36), which were crossed to an agronomically superior natural tetraploid apomictic genotype of B. brizantha (B140 - BRA003395). Three of them (HBGC313, HBGC 315, and HBGC324) were sexual and one (HBGC325) apomictic. Analyses of some cells in diakinesis revealed multivalent chromosome configurations, suggesting that genetic recombination and introgression of some genes could be present. The four hybrids had different types of meiotic abnormalities at various frequencies. Abnormalities related to irregular chromosome segregation due to polyploidy were common among these hybrids, and characterized by precocious chromosome migration to the poles, laggard chromosomes, both generating micronuclei in telophases and tetrads and, as a consequence, unbalanced gametes. One abnormality genotype-specific, related to spindle orientation (a putative divergent spindle mutation), was recorded for the first time in two of the hybrids, HBGC313 and HBGC325. The sexual hybrid HBGC324 had the lower rate of abnormalities, and it could be used as a female genitor in future crosses in the breeding program. The abnormalities present in these hybrids may impact fertility and affect seed production. Based on the results, HBGC324 is the single hybrid recommended to the breeding program. Hybrids must produce a good amount of viable seeds, besides good overall dry matter production and nutritive value, in order to be widely utilized and adopted in production systems. Due to pseudogamy, the desirable superior apomictic hybrids need viable pollen grains to fertilize the secondary nucleus of the embryo sac and thus ensure normal and vigorous endosperm development and plenty of seed set

Interação entre abelha Trigona hyalinata (Lepeletier, 1836) (Hymenoptera: Apidae) e Aethalion reticulatum Linnaeus, 1767 (Hemiptera: Aethalionidae) em Clitoria fairchildiana Howard (Papilionoideae)

The Aethalion reticulatum (Linnaeus, 1767) is an insect that feeds of the sap of several vegetal species and can live in symbiosis with ants from the genera Camponotus (Hymenoptera: Formicidae, Formicinae), attacking leaves and branches of many cultivated and native plants such as acacia-negra, cotton, aroeira, coffee, eucalyptus, citrus, etc. Some apparently commensal relationships can occur between leafhoppers and stingless bees, especially Trigona. In the present study we have observed the interaction between the irapuá bee Trigona hyalinata (Lepeletier, 1836) and the leafhopper of the stalk A. reticulatum in Clitoria fairchildiana Howard (sombreiro). The interaction between T. hyalinata and A. reticulatum was registered through digital photographs. The stimulation of the leafhopper for the release of the honeydew initiated when bees landed on the nymph�s and adult�s colony of A. reticulatum and stimulated the individuals by walking over them, mainly from the anterior region (head) to the posterior one (abdomen) of the leafhopper�s body. After that the bees touched their antennas at the distal part of the abdomen stimulating the production of the honeydew and readily sucked the substance. This interaction is mutually beneficial without necessarily implying obligate dependence or interdependence, and can promote a protection against leafhopper natural enemies. Nevertheless, the occurrence of a high leafhopper infestation associated to the intense activity of bees requesting honeydew may leave to depletion of the plant�s nutrients, affecting the development and/or of C. fairchildiana.A cigarrinha do pedúnculo Aethalion reticulatum (Linnaeus, 1767) é um inseto que se alimenta da seiva de várias espécies vegetais e pode viver em simbiose com formigas do gênero Camponotus (Hymenoptera: Formicidae, Formicinae), atacando folhas e ramos de inúmeras plantas cultivadas e nativas, tais como acácia-negra, algodoeiro, aroeira, cafeeiro, eucalipto, citros, etc. Algumas relações aparentemente comensais podem ocorrer entre cigarrinhas e abelhas sem ferrão, principalmente Trigona. No presente estudo, observamos a interação entre a abelha irapuá, Trigona hyalinata (Lepeletier, 1836) e a cigarrinha do pedúnculo, A. reticulatum em Clitoria fairchildiana Howard (sombreiro). A interação entre T. hyalinata e A. reticulatum foi registrada por meio de fotografias digitais. A estimulação da cigarrinha para a liberação de exsudato iniciava-se quando as abelhas pousavam sobre as colônias de ninfas e adultos de A. reticulatum e estimulavam os indivíduos andando por cima deles, principalmente da região anterior (cabeça) para a posterior (abdome) do corpo da cigarrinha. Posteriormente, as abelhas tocavam as antenas na parte distal do abdome estimulando a secreção de exsudato e prontamente sugavam essa substância. Esta interação é mutuamente benéfica, sem implicar necessariamente dependência ou interdependência obrigatória, e pode promover uma proteção contra os inimigos naturais da cigarrinha. Todavia, a ocorrência de uma alta infestação de cigarrinhas, associada à intensa atividade de abelhas solicitando honeydew pode levar a depleção de nutrientes da planta, afetando o desenvolvimento e/ou reprodução de C. fairchildiana