Maria Jane Cruz de Melo Sereno

TOLERÂNCIA AO ALUMÍNIO EM PLÂNTULAS DE MILHO

A selecao para tolerância ao aluminio e complicada pela desuniformidade natural dos solos e pela dificuldade de avaliar danos na raiz. Assim sendo, e importante desenvolver metodos eficientes de caracterizacao da tolerância ao aluminio em condicoes controladas de ambiente. O presente trabalho teve por objetivo adequar o metodo de solucao minima para a avaliacao da tolerância ao aluminio em genotipos de milho. O trabalho consistiu de dois experimentos. O primeiro foi feito para ajustar o metodo de avaliacao atraves do emprego de solucao minima, e o segundo, para avaliar um conjunto de 22 genotipos de milho fornecidos pela Empresa Agroeste Sementes Ltda. A avaliacao dos genotipos foi realizada com uma solucao que continha diferentes concentracoes de aluminio e calcio. As medias para todas as variaveis analisadas mostraram a diferenca entre os hibridos e entre as concentracoes de aluminio empregadas. As concentracoes de 6mg-1 de aluminio e 40mg-1 de calcio foram consideradas mais eficientes para a discriminacao da tolerância ao aluminio, sendo posteriormente empregadas para o trabalho com as linhagens. No segundo experimento, os resultados possibilitaram identificar linhagens com tolerância ao aluminio.

Capacidade combinatória de genótipos de milho para tolerância ao encharcamento do solo

In southern Brazil, corn could be an alternative for cultivation in flooded areas. However, the development of genotypes tolerant to flooding is fundamental to make this option economically feasible. The objective of this paper was to determine the general and specific combining ability and reciprocal effect for flooding tolerance in corn genotypes. The analysis was based on a diallel cross among four inbreds: two flooding tolerant (CT954280 and CT954330) and two sensitive inbreds (CT966200 and CT966208). The experiment was conducted in 2000 and 2001 under greenhouse conditions at Embrapa Clima Temperado, Pelotas, RS. Root dry matter, plant dry matter, plant high, root length, and leaf chlorophyll content were measured. Genetic variability among the inbreds was detected. Both additive and non-additive effects were important in the determination of the inheritance of flooding tolerance in corn. The correct choice of the female parent is fundamental for tolerant hybrids production, since maternal effects were relevant. Among the analyzed genotypes, the inbred CT954330 presented the highest GCA and may be indicated as a preferential progenitor in crossings that aim to increase flooding tolerance.

Genetic variability in maize and teosinte populations estimated by microsatellites markers

Wild species are important sources of genetic variability and may be exploited by breeding programs. Crosses between teosinte and maize occur freely and teosinte serves as genetic source of agronomic traits for introduction in maize. The objective of this study was to estimate genetic variability among and within maize and teosinte populations (Zea mays mexicana). Two sweet maize populations (BR400 and BR402), two common maize populations (Suwan and Pampa) and one teosinte population were analyzed using microsatellites markers. Results indicated that 64,5% of the variation was detected within the populations, suggesting the possibility of obtaining genetic progress by selection within each population. The analysis with 25 microsatellites loci enabled the identification of 92 alleles with a mean of 3.7 alleles per locus. The average Polymorphism Information Content (PIC) was 0.52. The percentage of polymorphic loci varied from 64% in the BR400 and Pampa populations to 80% in the teosinte population. The estimated genetic distance confirmed the genomic similarity of maize and teosinte.

Herança da estatura de planta e do comprimento da panícula principal no cruzamento entre Avena Sativa L. e Avena Sterilis L.

The wild species Avena sterilis L. has been widely used for crossing with cultivated oat. The high affinity between them enables an increase in genetic variability and transference of important agronomic genes. However, undesirable characters such as great plant height and length of the panicle can be transferred to progenies. These characters were analysed to evaluate the genetic variability and inheritance in crossing between Avena sativa L. and Avena sterilis L. Estimates of phenotypical and genetical variances were high while the environmental variance was low, providing a high broad sense heritability. The additive gene effect was the most important for explaining the genetic variation for both characters.

Conservação e germinação in vitro de pólen de milho (Zea mays subsp. mays)

The storage of pollen can be considered an important tool for maize breeding programs, allowing to preserve, under artificial conditions, the viability of male gametes and extend the possibilities of crossings regardless of flowering time of parental varieties. This study aimed to evaluate the culture media for in vitro germination of corn pollen and analyze storage conditions. To examine viability, six different culture media containing sucrose, boric acid, calcium chloride and agar were evaluated. For pollen preservation, two temperatures (4 oC and -20 oC) and two agents of pollen dehydration (silica gel and hydrated calcium chloride) were evaluated. The high values of pollen viability up to 30 days of storage indicate that dehydration in silica gel and storage at 4 oC preserve the viability of corn pollen. The culture medium that provided the highest germination rate in vitro was the composition of 0.7% agar, 17% sucrose, 0.01% boric acid and 0.03% calcium chloride hydrate.

Avaliação de embriogênese somática em cultivares de aveia (Avena saliva L.)

Nine oat genotypes were cultivated in vitro to evaluate callus initiaton and subsequent somatic embryogenesis. The immature embryo were submited to different protocola (MURASHIGE & SKOOG (1962) medium with differents hormones dosages). The protocols tested caused differences in somatic embryogenesis, and the best of them was selected to continue the research. After a month in subculture medium the cali were evaluated concerning embryoid porcentage, and showed differences according to genotype in experiment 2, UFRGS 7 and UFRGS 8 presented superior means. The covariance analysis revealed that in some genotypes this parameter is important.

Avaliação de genótipos de trigo hexaplóide quanto a tolerância a toxicidade do alumínio

Aiming to test and improve lhe method of evaluation of hexaploid wheat (Triticum aestivum L.) to aluminum toxic levels in nutritive solution. Five genotypes with known reaction to toxic aluminum (Al+++) were tested in nutritivo soluction in three different Al+++ concentrations (4, 6 e l0ppm), in two experiments. The results allowed the equipament ajustment, the choice of best evaluation method to select tolerant wheat genotypes to toxic Al+++ concentrations.

Indução à macho-esterilidade e formação de sementes em genótipos de trigo

The genetic variability is importam for lhe development of new genotypes in breeding programs. This variability is obtained through genetic recombination in plants originated from crosses involving contrating genotypes. However, artificial cresses in wheat is a difficult task because of its selfpolinization. The induction of male-sterility may be na altemative for the production of hybrid seeds. The present work had the following objectives: evaluate the efficiency of the gametocide 2-chloroethilphosphonic (Ethrel) in the induction of maleterility in wheat, estimate the frequency of crosspoilination in wheat genotypes cultivated in the field, and verify the effect of Ethrel in the production o f wheat hybrid seeds in the field. The product was appiied in five wheat varieties in three different doses in the pre-booting development stage, and the variety BR 43 was used as tester to verify the frequency of crossing. The evaluated traits were: percentage of viable pollen, number of grains produced in protected ears, percentage of artificial and natural cross-poilination. The results indicated that the product Ethrel was efficient in the induction of male-sterility in ali tested genotypes; however, the ovules were aiso affected, evidenced by the reduction in the number of seeds produced in piots treated with the gametocide. The doses of 10l/ha and 20l/ha caused accentuated pollen sterility; on the other hand, na increment in the production of hybrid seeds was not observed. As a consequence, it is necessary to adjust the technique of appiication of Ethrel for the production of hybrid seeds in wheat.