Alfredo Augusto Cunha Alves

Effect of elevated CO2 concentration and nitrate: ammonium ratios on gas exchange and growth of cassava (Manihot esculenta Crantz)

AimsThis study evaluated how different nitrogen forms affect growth and photosynthetic responses of cassava to CO2 concentration.MethodsCassava was grown in 14-L pots in a greenhouse at 390 or 750xa0ppm of CO2. Three nitrogen treatments were applied: (a) 12u2009mM NO3−, (b) 6u2009mM NO3−u2009+u20096u2009mM NH4+, and (c) 12u2009mM NH4+.ResultsThirty-six days after treatments began, plants grown under elevated CO2 and fertilized only with NO3− (750_NO3−) had photosynthetic rates similar to plants grown under 390_NO3−, indicating significant photosynthetic acclimation to CO2. In contrast, photosynthetic rates at elevated CO2 increased as NH4+ increased in the nutrient solution, such that photosynthetic acclimation was reduced for plants fertilized with only NH4+. However, this positive effect of NH4+ on photosynthesis was not observed in more advanced growth stages, and the toxic effects of NH4+ severely reduced total dry mass for these plants measured at the end of the experiment.ConclusionsOur results indicate that cassava will respond with increased biomass accumulation in response to raising atmospheric CO2 levels, and that N form can have an important impact on the photosynthetic response. However, the positive effect of NH4+ fertilization on cassava photosynthetic CO2 response eventually led to a toxicity problem that reduced biomass production. The challenge is to determine how to manage NH4+ fertilization so that the photosynthetic benefit observed in the initial phase may persist throughout the crop cycle.

Viability, production and morphology of pollen grains for different species in the genus Manihot (Euphorbiaceae)

The objective of this work was to characterize the viability, production and morphology of pollen for different species in the genus Manihot. Floral buds from Manihot accessions were collected from two germplasm banks at Embrapa Cassava & Fruits. The viability of the pollen was assessed via colorimetric, in vitro and in vivo assays. The diameter of the pollen grains was determined by measuring the transversal length of the grain. The experimental design was entirely randomized. Studies on pollen ultrastructure were performed via scanning electron microscopy. Pollen viability was high in the colorimetric tests and intermediate in vivo tests; there was no germination in the in vitro tests. The average production for all accessions was 1,253 pollen grains per floral bud. The size of the pollen grains varied from 132 to 163 µm in the wild accessions, and 129 to 146 µm in the cultivated accessions. The pollen grains for all accessions were very large, apolar, spherical as well as inaperturate, with an exine ornamented with pila organized in a Croton pattern. The wild accessions, in general, produced more and larger pollen grains compared with the cultivated accessions.

Droplet-vitrification and morphohistological studies of cryopreserved shoot tips of cultivated and wild pineapple genotypes

AbstractGermplasm conservation of pineapple [Ananas comosus (L.) Mer.] is crucial to preserve the genus’ genetic diversity, to secure material for genetic improvement and to support innovative and new research. Long-term conservation is accomplished through cryopreservation, that is done by storing cells or tissues at ultra-low temperature in liquid nitrogen (−196xa0°C). Droplet-vitrification, a combination of droplet freezing and solution-based vitrification, was used to establish a protocol for cryopreservation of pineapple genetic resources. This protocol was tested on cultivated and wild pineapple genotypes to establish a long-term germplasm security duplicate as well as to investigate cryo-injuries in the tissues by means of histological techniques. Excised shoot tips (0.5–1xa0mm with one primordial leaf) of different pineapple genotypes were precultured for 48xa0h on solid MS medium containing 0.3xa0M of sucrose. Three PVS2 exposure times (30, 45 and 60xa0min) were tested. The results showed high post cryopreservation survival for all genotypes evaluated. The best PVS2 exposure time varied according to genotype, although 45xa0min gave the best survival for the majority of genotypes. The technique was highly efficient in cryopreserving meristem shoot tips of different pineapple genotypes, and was also less laborious than techniques previously reported. This is a first report on application of the droplet-vitrification technique to diverse genotypes of cultivated and wild pineapples and the first report on histological changes occurring in cryopreserved Ananas tissue.n

Development of interspecific hybrids of cassava and paternity analysis with molecular markers

The present paper demonstrates the development of interspecific hybrids between Manihot esculenta Crantz ssp . esculenta ( Mee ) and M. esculenta Crantz ssp . flabellifolia ( Mef ) and paternity analysis using microsatellite markers [simple sequence repeat (SSR)]. Three Mef accessions (FLA005, FLA025V and FLA029V) were used for crosses with varieties of Mee : Saracura, Aipim Bravo, COL 1725, Aipim Rosa, Abobora, Parana and PER334. The paternity of the interspecific hybrids was investigated using 24 SSRs. The observed heterozygosity ( Ho ), polymorphic information content ( PIC ), probability of identity ( PI ) and paternity exclusion ( PE ) were evaluated. The rate of breeding success varied from 17 to 92%, and an average of two pollinations were required for each generated hybrid plant. The Ho value ranged from 0·11 to 0·92, and the PIC value ranged from 0·12 to 0·59. The uneven distribution of allele frequencies was accompanied by a high PI average (0·56). However, the combined PE for 21 loci was 0·99, which allows for the determination of the paternity of the hybrids with good discriminatory power. Of the 74 hybrids evaluated, 0·82 had their paternity confirmed using microsatellite markers. Discriminant analysis of principal components (DAPC) indicated the presence of eight clusters, of which, one was composed of only Mef varieties and the supposed hybrid Fla52Sar-H7, which was a product of apomixis. The parent Mee and hybrids were allocated in the other seven clusters. The data obtained demonstrate that SSR markers can be routinely used in breeding programmes to verify the paternity of interspecific crosses of cassava.

PRODUÇÃO E TAMANHO DE PÓLEN DE VARIEDADES DOMÉSTICAS E ESPÉCIES SILVESTRES DE MANDIOCA

Estudos de producao e morfologia de polen em variedades domesticadas e silvestres demandioca sao importantes para subsidiar o melhoramento genetico da cultura. O objetivo do trabalhofoi comparar a producao e o tamanho de graos de polen entre diferentes especies do genero Manihot.Especies silvestres, M. violacea, M. dichotoma, M. peruviana e M. flabellifolia, e tres variedades daespecie cultivada, M. esculenta, foram utilizadas para essa avaliacao. Tres flores de cada genotipoforam coletadas de botoes florais no estadio de balao (pre-antese). A contagem do polen foi realizadaem microscopio na ocular de 10X e o diâmetro do polen foi determinado pelo comprimentotransversal do grao utilizando uma ocular micrometrica. A analise de variância foi efetuada por meiodo programa SAS e a comparacao das medias feita com o teste de Tukey a 5% de probabilidade. Omaior numero de polen observado entre os genotipos silvestres foi na especie dichotoma, comproducao media de 3638 graos de polen/flor enquanto que a menor producao foi observada nogenotipo de flabellifolia, com producao media de 579 graos. Nas variedades de mandioca o numerode graos de polen medio por flor variou de 613 a 932. A variavel tamanho de polen variou de 130,2μm em uma variedade domesticada a 160,6 μm em um genotipo silvestre. O resultado obtido pelaanalise de variância da producao e tamanho de polen permitiu concluir que estatisticamente existepelo menos um contraste entre as medias dos tratamentos avaliados em nivel de 5% deprobabilidade (p<0,05).