In vitro multiplication of cassava varieties / Multiplicação in vitro de variedades de mandioca / Multiplicación in vitro de variedades de mandioca

The implantation of a model of sustainable development for agriculture can happen with the contribution of the mandiocultura. But for this, culture needs to be strengthened. In vitro propagation is an instrument for this purpose. Micropropagation can provide growers with large quantities of vigorous and healthy cassava seedlings in a short time. The objective of this study was to evaluate the in vitro establishment of four varieties of cassava cultivated in the municipality of Colorado do Oeste, State of Rondônia, popularly known as Arara, Caturra, Cacau Vermelha and Roxinha. For that, an experiment was carried out in the Laboratory of In Vitro Cultivation at the Pole of Technological Innovation of the University of Cruz Alta (UNICRUZ), with a completely randomized design in a 4 x 2 factorial scheme, with 6 replications. The treatments consisted of explants grown in Murashige and Skoog (MS) medium without the presence of growth regulator and MS medium supplemented with of 6-benzylaminopurine (BAP). The results indicate that the mean contamination percentage of the explants was 47.19%, differing among the varieties. The best growth response in culture media, in the multiple comparison of means (Scott-Knott's test, 5%), was obtained with MS medium without BAP addition, with significant difference between varieties. Under the conditions of this experiment, it was evidenced that micropropagation is a viable tool for obtaining varieties of interest, with desired phytosanitary qualities, with varietal and large-scale authenticity.(AU)

A implantação de um modelo de desenvolvimento sustentável para a agricultura pode acontecer com a contribuição da mandiocultura. Mas para isso, a cultura precisa ser fortalecida. A propagação in vitro é um instrumento para este fim. A micropropagação pode proporcionar aos produtores grande quantidade de mudas de mandioca vigorosas e sadias em um curto espaço de tempo. O objetivo deste trabalho foi avaliar o estabelecimento in vitro de quatro variedades de mandioca cultivadas no município de Colorado do Oeste, Rondônia, popularmente conhecidas como Arara, Caturra, Cacau Vermelha e Roxinha. Para isso, foi realizado um experimento no Laboratório de Cultivo In Vitro no Polo de Inovação Tecnológica da Universidade de Cruz Alta (UNICRUZ), com delineamento inteiramente casualizado em esquema fatorial 4 x 2, com 6 repetições. Os tratamentos consistiram em explantes cultivados em meio Murashige e Skoog (MS) sem a presença de regulador de crescimento e meio MS suplementado com 6-benzilaminopurina (BAP). Os resultados indicam que a porcentagem média de contaminação dos explantes foi de 47,19%, diferindo entre as variedades. A melhor resposta de crescimento em meios de cultura, na comparação múltipla de médias (teste de Scott-Knott, 5%), foi obtida com meio MS sem adição de BAP, com diferença significativa entre as variedades. Nas condições deste experimento, ficou evidenciado que a micropropagação é uma ferramenta viável para obtenção de variedades de interesse, com qualidades fitossanitárias desejadas, com autenticidade varietal e em larga escala.(AU)

La implantación de un modelo de desarrollo sostenible para la agricultura puede suceder con el aporte de la mandiocultura. Pero, para eso, la cultura necesita ser fortalecida. La propagación in vitro es un instrumento para ese fin. La micropropagación puede proporcionar a los cultivadores grandes cantidades de plántulas de mandioca vigorosas y saludables en poco tiempo. El objetivo de esta investigación ha sido evaluar el establecimiento in vitro de cuatro variedades de mandiocas cultivadas en el municipio de Colorado del Oeste, Rondônia, popularmente conocidas como Arara, Caturra, Cacau Vermelha y Roxinha. Para eso, se realizó un experimento en el Laboratorio de cultivo in vitro en el Polo de Innovación Tecnológica de la Universidad de Cruz Alta (UNICRUZ), con delineamiento completamente casualizado en esquema factorial 4 x 2, con 6 repeticiones. Los tratamientos consistieron en explantes cultivados en medio Murashige y Skoog (MS) sin la presencia de regulador de crecimiento y medio MS suplementado con 6-bencilaminopurina (BAP). Los resultados indican que el porcentaje de contaminación promedio de los explantes fue de 47.19%, diferenciándose entre las variedades. La mejor respuesta de crecimiento en medios de cultivo, en la comparación múltiple de medias (prueba de Scott-Knott, 5%), se obtuvo con medio MS sin adición de BAP, con una diferencia significativa entre las variedades. Bajo las condiciones de este experimento, se evidenció que la micropropagación es una herramienta viable para obtener variedades de interés, con cualidades fitosanitarias deseadas, con autenticidad varietal y de gran escala.(AU)

Evaluation of cassava plants generated by somatic embryogenesis at different stages of development using molecular markers

Background: Cassava (Manihot esculenta Crantz) is a crop that is high in carbohydrates in the roots and in protein in the leaves, important for both human consumption and animal feed, and also has a significant industrial use for its starches. In this study we evaluated the genetic variability with molecular markers in different stages in micropropagated plants from somatic embryos of Venezuelan native clone 56. Results: Three markers were used: ISTR, AFLP and SSR, finding that ISTR showed the highest polymorphism among individuals tested. With AFLP a high similarity between the evaluated individuals was observed and with SSR total monomorphism was seen. Using cluster analysis it was found that individuals from an embryo labeled as fasciated at the beginning of the somatic embryogenesis process were grouped as independent of the other plants when analyzed at the acclimatization stage. The differences found with the different markers used are discussed. In field trials, micropropagated plants had a yield between 4 and 5 times the average yield of cassava in Venezuela. Conclusion: Despite variability in terms of DNA markers, somatic embryogenesis is suitable for mass propagation of highly performing cassava clones.

Molecular analysis of apomixis in cassava

Cassava is the main staple for more than 800 million people in the tropics. It is propagated vegetatively by stem cuttings, which maintains superior genotypes but favors disease accumulation and spread. In this report, we present the results of the screening of the progeny and the second generation of the clone UnB 307 for apomixes using microsatellites. A total of 29 plants were screened, representing the maternal plant, its first and second generations that were left to open pollination. About 20% of the offspring were rated as genetically identical plants. This result confirms the facultative apomictic nature of cassava, with high environmental effect.

Breeding cassava for apomixis

Apomixis genes have been successfully transferred to cassava (Manihot esculenta) by hybridizing it with the wild species, M. glaziovii. The interspecific hybrid of cassava and M. glaziovii was exposed to open pollination during three subsequent generations. Seven sibs and the maternal progenitor of the fourth generation were genotyped using five microsatellite loci previously developed for cassava. All sibs were identical with each other and with their maternal progenitor. Sibs from M. glaziovii proved to be identical when examined by the same microsatellite loci. This evidence leads to the conclusion that apomixis does occur in wild-cassava relatives and apparently has played an important role in Manihot speciation. This is the first report of nearly 100% apomixis.

Apomixis and cassava

Apomixis means seed formation without fertilization. In cassava (Manihot esculenta) it is an alternative to reproduction by cuttings, which normally transmits pathogens and leads to an accumulation of viral and bacterial diseases. Apomixis also assures preservation of heterosis and avoids genetic segregation. It occurs in wild relatives of cassava and has been transferred successfully from Manihot glaziovii and M. neusana. It is facultative, and occurs at a low frequency, ranging from 1-2, and apparently is genetically different from apomixis in other crops. With selection, the frequency can reach 13. Apomixis in cassava is frequently associated with aneuploidy but it does occur in some diploid types. It is due to the formation of aposporic sacs, which can easily be detected by clearing tissue preparations. Apomixis appears to have played an important role in speciation during the evolution of Manihot, since it leads to the maintenance and perpetuation of sterile interspecific hybridization. The use of apomixis in cassava breeding could lead to a boom in line improvement and commercial production. In addition to preserving superior genotypes, avoiding contamination of new plants, it would enable international programs to export their germplasm to destination countries. This would allow the use of superior genotypes even if apomixis occurs at a low frequency. A scheme to maximize benefits is to use diploid apomictic clones as maternal parents, which can be crossed with pollinators of polyploid interspecific hybrids, followed by selection among the progeny of new apomictic types that combine the heteroses of both interspecific hybridization and polyploidy. In addition, they acquire favored genes that have been transferred from the wild to the commercial crop