Apomixis

Cytogenetic and anatomic behavior of cytochimeras and total polyploids in cassava

D. Y. Hashimoto-Freitas and Nassar, N. M. A., “Cytogenetic and anatomic behavior of cytochimeras and total polyploids in cassava”, vol. 12, pp. 4879-4894, 2013.

Cassava periclinal cytochimeras, cultivars, and interspecific hybrid and polyploid types were studied in relation to embryonic, cytogenetic, and anatomical behavior. Their apical shoots, pollen grains, male and female buds, roots, stomata, and flowering period were analyzed. Chimeras exhibited increased size of L1 and L2 cells. Polyploidy led to enlargement of stomata in chimeras whereas L2 gave tetraploid chromosome configurations, tetrad irregularity, decrease of pollen viability, and increase in frequency of polyembryo sacs.

Sexual reproduction development in apomictic Eulaliopsis binata (Poaceae)

L. Liu, Li, J. J., Ouyang, Y. D., and Yao, J. L., “Sexual reproduction development in apomictic Eulaliopsis binata (Poaceae)”, vol. 10, pp. 2326-2339, 2011.

Apomixis is a particular mode of reproduction that allows progeny formation without meiosis and fertilization. Eulaliopsis binata, a tetraploid apomictic species, is widely used for making paper, rope and mats. There is great potential for fixation of heterosis in E. binata due to autonomous endosperm formation in this species. Although most of its embryo sac originates from nucellus cells, termed apospory, we observed sexual reproduction initiation in 86.8 to 96.8% of the ovules, evidenced by callose deposition on the walls of cells undergoing megasporogenesis.

Cytogenetic and molecular analysis of an apomictic cassava hybrid and its progeny

N. M. A. Nassar, Gomes, P. T. C., Chaib, A. M., Bomfim, N. N., Batista, R. C. D., and Collevatti, R. G., “Cytogenetic and molecular analysis of an apomictic cassava hybrid and its progeny”, vol. 8, pp. 1323-1330, 2009.

An interspecific hybrid between cassava and Manihot glaziovii acquired an apomixis gene from the parent M. glaziovii. This hybrid was exposed to open pollination during three subsequent generations. Seven sibs and the maternal progenitor of the fourth generation were genotyped using six microsatellite loci previously developed for cassava. All sibs were identical with each other and with their maternal progenitor. Sibs of selfed M. glaziovii proved to be identical when examined with these microsatellite loci.

Breeding cassava for apomixis

N. M. A. Nassar and Collevatti, R. G., “Breeding cassava for apomixis”, vol. 4, pp. 710-715, 2005.

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.

Molecular analysis of apomixis in cassava

N. M. A. Nassar, Kalkmann, D. C., and Collevatti, R., “Molecular analysis of apomixis in cassava”, vol. 5, pp. 487-492, 2006.

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.

The synthesis of a new cassava-derived species, Manihot vieiri Nassar*

N. M. A. Nassar, “The synthesis of a new cassava-derived species, Manihot vieiri Nassar*”, vol. 5, pp. 536-541, 2006.

A new species was synthesized artificially by chromosome doubling in a hybrid. The ensuing polyploid type exhibits an apomictic nature and maintains its morphological characteristics in the progeny. It showed a frequency of multiembryonic sacs of 29% in the ovules examined, whereas sacs were absent in the diploid type.

*In honor of deceased Professor Vieira who dedicated a part of his life to cassava breeding

Cassava genetic resources and their utilization for breeding of the crop

N. M. A. Nassar, “Cassava genetic resources and their utilization for breeding of the crop”, vol. 6. pp. 1151-1168, 2007.

Wild cassava relatives are perennials and vary in growth pattern from nearly acaulescent subshrubs to small trees. They have been used as a source of useful characters such as high protein content, apomixis, resistance to mealybug and mosaic disease, and tolerance to drought. Indigenous clones are a potential source of β-carotene and lycopene. Apomixis genes have been transferred to the crop successfully through interspecific hybridization, and apomictic clones arising from these hybrids are now being grown at the Universidade de Brasília.

Apomixis and cassava

N. M. A. Nassar, “Apomixis and cassava”, vol. 1, pp. 147-152, 2002.

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.

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