Rita Bordignon

Identification of reciprocal hybrids in citrus by the broadness of the leaf petiole wing

Broadness of leaf petiole wing (WB) was investigated as a morphological marker for screening hybrids of the very narrow-winged species Citrus limonia and C. sunki with broad-winged species C. aurantium and C. sinensis. Controlled polinizations produced over 500 reciprocal hybrids with potential in the ongoing rootstock breeding program identified by the Pgi-1 and Prxa-1 isozyme loci. Measurement ratios WB/leaf length, WB/leaf broadness and WB/petiole length identified 86 to 91% of the reciprocal hybrids produced. However, visual classification of WB was an equally efficient but much easier and faster method. It can be very useful in breeding programs when large number of plants have to be screened or when isozyme, RFLP or RAPD laboratories are not available.

Isoenzimas na identificação precoce de híbridos e clones nucelares no melhoramento de citros

Um dos problemas relacionados ao melhoramento de citros e a poliembrionia e a consequente dificuldade, apos cruzamentos controlados, de distinguir clones nucelares dos hibridos. Estudou-se um metodo para eletroforese de isoenzimas em gel de amido para doze sistemas isoenzimicos, desenvolvendo-se procedimento apropriado para a resolucao simultânea dos sistemas fosfatase acida, peroxidase anodica e catodica, glutamato oxaloacetico transaminase, fosfoglucoisomerase, fosfoglucomutase e enzima malica. Caracterizaram-se por esses sistemas 31 clones de citros com possivel interesse para o programa de melhoramento do IAC. Estao envolvidos 7 locos e 25 alelos, permitindo uma identificacao precoce de hibridos antes do plantio no campo para avaliacoes agronomicas. Implicacoes desses estudos basicos no melhoramento e na determinacao da taxa de seedlings nucelares de porta-enxertos comerciais sao discutidas.

Variabilidade genética do rendimento intrínseco de grãos em germoplasma de Coffea

O rendimento intrinseco do cafe, relacao percentual entre a massa de dois graos normais tipo chato e do respectivo fruto que os contem, foi estudado em seis grupos de germoplasma de Coffea, com o objetivo de se conhecer a variabilidade genetica para essa caracteristica. Investigou-se o rendimento intrinseco de Coffea arabica em um grupo de cinco cultivares de porte baixo, em outro contendo 22 cultivares e selecoes e, ainda, em outro grupo com 79 cultivares, variedades e formas botânicas, mutantes e acessos da Etiopia. Em C. canephora, foram analisados tres acessos da variedade kouilou e 10 acessos da variedade robusta. Investigaram-se ainda, outras oito especies do genero Coffea. Observou-se consideravel variabilidade genetica tanto entre representantes de C. arabica quanto de C. canephora, assim como entre as diferentes especies do genero Coffea. A amplitude de variacao nos valores de rendimento intrinseco referente ao ultimo grupo foi bem maior que a de qualquer outro grupo estudado. A magnitude das variacoes observadas e as implicacoes economicas do rendimento intrinseco indicam que essa caracteristica pode ser utilizada como um criterio adicional de selecao no melhoramento de C. arabica e C. canephora.

A tristeza dos citros e suas implicações no melhoramento genético de porta-enxertos

Brazil is the world leading citrus producer and historically, tristeza is the most serious disease in economic importance. Tristeza is caused by a single strand RNA closterovirus, Citrus Tristeza Virus (CTV), is disseminated in almost all citrus regions of the world. It is transmitted by grafting and by several species of aphids mainly Toxoptera citricida. There are several virus strains, causing variable symptoms in the majority of species and related genera of Citrus. Cross-protection by mild virus strains is an efficient technique for protecting very sensitive scions in Brazil and elsewhere. Methods for detecting and characterizing virus strains are classically based on the reaction symptoms of specific varieties and clones. However, development of serological and molecular methods have allowed progress in the characterization and in monitoring the spread of the disease. Plants may be infected with more than one strain that can undergo genetic recombination, show differential transmissibility by the vector aphids, have composition of the strain complex altered by drastic pruning, temperature, and also segregate among budwoods, or by sub-culture in different clones. Smaller defective RNAs are often associated with normal CTV particles, some correlated with symptoms of seedling yellows. Efficient control is achieved by favorable combinations of scions and rootstocks. They react in predictable interactions dependent on both, the capability to multiply the viruses and to tolerate their presence in phloem tissues. These peculiarities have important implications on practical cultivation and on the genetic improvement of scions and rootstocks. This review discuss also the reaction of grafted and non-grafted plants, and highlights problems, basic concepts and relevant implications for citrus rootstock improvement.

Segregações gaméticas de locos isoenzímicos em porta-enxertos de citros e suas contribuições alélicas na formação de híbridos

The rootstock clones Rangpur lime(Citrus limonia), Sunki mandarin (C. sunki), Sour orange (C. aurantium) and Trifoliate orange(Poncirus trifoliata) were studied by discontinuous horizontal starch gel electrophoresis as to genotypes and segregations of the isozyme loci Pgi-1, Pgm-1, Got-1, Got-2, Prxa-1, Aps-1 and Me-1 as well as their relative allelic contributions to more than 400 hybrids between them. The loci Aps-1 and Me-1, although useful for identifying hybrids are homozygous in the genitors and consequently were disregarded in the studies of segregation and allelic contribution. In Trifoliate orange, the duplicate Got-2 locus previously described as having the genotype MT.SS is actually SS.MT being S an allele of F in Sunki (FF.MM) and of F and M in Sour orange (FM.MM). M and T of the duplication are alleles of M of the homozygous locus of Sour orange and Sunki as determined by the banding pattern observed in the hybrids and by the formation of the correspondent intralocus heterodimers. Among 27 segregations for the five loci investigated, statistically significant distorted segregations, occurred in six (22%) of them. Considering the absence of selection provided by ideal conditions of germination, handling of young hybrid embryos in Petri dishes and determination of genotypes at the first or second leaf pair, the results probably reflect distortion in the relative proportion of alleles in the gametes of the genitors, differential transmission of the alleles or distinct viability of their bearers in the hybrid zygotes. Due to the codominance of the alleles it was possible, from the genotypes of the hybrids, to deduce the relative contribution of each allele of the heterozygous loci of the genitors. Genotypic distortions did not come from the Trifoliate orange, occurred in one locus of Sour orange and Sunki mandarin and was traced back to Rangpur lime in the three tested loci. Such marked distortions are congruent with a possible interspecific hybrid origin of Rangpur lime and also illustrate the difficulty of genetic studies in citrus involving genotype proportions in zygotic progenies.

Influências ambientais no rendimento intrínseco do café

It was studied the influence of several environmental factors on the intrinsic outturn (RI) of coffee, ratio between the weight of two flat beans and the respective fruit containing them. The RI decreased up to 18% in fruits from unripe (green) to overripe (raising) stage. In seven localities evaluated fruit RIs varied up to 12%. In two different sites of the same locality variation on RI up to 6% was observed. It was observed a difference of 2% among four experimental plots in the same site. Plants of the same cultivar grown in a single experimental plot displayed RI with differences up to 3,7%. In the same locality variations up to 330 meters in altitude were positively correlated with variations up to 4,4% in the RI. Regarding to the influence of the fruit position within the plant it was observed that RI decreased, up to 4,4% if the fruits are located farther from the orthotropic branch, 1,5% in the East side and 0,5% at the middle and upper parts of the plants. The results pointed out that there are considerable environmental influences on the intrinsic outturn of coffee. For breeding purposes, selection for higher RIs must be based on standard sampling as to ripening stage, position in the plant, and be representative of at least 10 plants of uniform progenies evaluated in the same experimental plot.

Evidência isoenzímica sobre a origem interespecífica do café Piatã

Years ago it was found in a field of Coffea arabica (2n = 44) a coffee tree different from any other known so far. Initially it was thought to be an autotetraploid either of C. liberica (2n = 22) or of C. dewevrei (2n = 22). Morphological and cytological studies of this tree and its progeny, designated by the prefix C387 of the Department of Genetics, IAC and named Piata, indicated that it was probably a natural hybrid originated from the fusion of a normal gamete (n = 22) of C. arabica and an unreduced gamete (2n = 22) of C. dewevrei. In the present study the isoenzyme banding patterns for the enzymes PGI, PGM and ADH of the seeds endosperm of Piata confirmed its interspecific origin. The alleles of combination of C. dewevrei and C. arabica for the aforementioned isoenzymes is peculiar and distinct for these species, and such alleles segregate in the seeds of the Piata. Isoenzymatic studies on seeds showed also that Piata coffee is self-compatible, and not self-incompatible as it was believed. Indeed, autogamy is quite frequent in the Piata coffee. Similar analyses may be useful for the identification of other natural hybrids among Coffea species. This could be of great value for genetic and evolution studies, and breeding of coffee, where the knowledge of the origin, genotype constitution and reproductive biology of the plants is important.

Yield, maturation, and beverage quality of arabica coffee progenies under selection in Rondonia state, Brazil

In this paper, we studied coffee bean yield, maturation, and other characteristics of special progenies of Arabica coffee (Coffea arabica L.) grown under high temperatures in a low altitude region in the state of Rondonia, Brazil. We evaluated 29 progenies developed by the Instituto Agronomico de Campinas ? IAC, namely, 24 F2BC2 progenies of Obata (C. arabica with introgressions of C. canephora) x (C. eugenioides 4n x C. arabica), three F3 progenies of Catuai x Glaucia, and two H419 lines. Seven cultivars were used as controls. A randomized block design was used with three replications, spacing of 3.0 × 1.0 m, and ten plants per plot. All the crop seasons showed a significant difference for the hulled coffee yield trait. In combined analysis, significant difference was detected among progenies, among controls, and in the progeny vs control contrast. In the average of the four harvests, hulled coffee yield was 29.30 bags ha-1. The F2 progeny Obata x (Catuai x EUG DP x MN) C.1594 stood out from the others with a mean yield of 47.37 bags ha-1. The cultivars received beverage scores from 40 to 62, ?rioysh? to ?hard? beverage classification, while the progenies had scores from 40 to 80, ?rio? to ?barely soft? beverage classification. In regard to the maturation cycle, eleven progenies were late (April), eleven intermediate (March), and seven early (February). For continuity of advancement of generations, 104 plants were selected, derived from 22 progenies with the best productive performance, late maturation cycle, and good beverage quality.