Evidence of apomixis in cassava (Manihot esculenta Crantz)

Abstract

Apomixis maintains heterosis and avoids transmission of systemic pathogens which accompany vegetative propagation of cassava. An embryonic study of cleared ovules of two cassava clones in toto showed them to be of aposporic nature. Cytogenetic analysis of the two clones revealed an aneuploid structure (2n + 1) in apomictic individuals, whereas it was 2n in the sexually reproduced plants.

Wild Manihot species: botanical aspects, geographic distribution and economic value

“…Cross-pollination leads to the formation of extremely heterozygous gene pools. Being allopolyploid species, partially apomictic, and having weak barriers in addition to its allogamous nature, has led to the rapid speciation of this group and formation of the large number of species (Nassar et al, 1998b;Nassar, 1999Nassar, , 2000cNassar, , 2001aNassar, ,b, 2002a. Table 1 lists the most important species from an economic viewpoint, along with their names and classification according to the monograph by Rogers and Appan (1973).…”

“…These wild species proved to be potential sources for other traits such as high protein content (Jennings, 1959;Nassar and Costa, 1978) compared to low protein in cassava (Nassar and Dorea, 1982;Nassar and Marques, 2006). Restoring seed-fertility (Jennings, 1962;Nassar, 2004a), apomixis (Nassar et al, 1998a(Nassar et al, ,c, 2000Nassar, 2000b;Nassar and Collevatti, 2005), resistance to mealy bug, and tolerance to drought-prone environments (Nassar, 2000c) were useful characters gained from wild species. This review updates previous reports by Nassar (1999Nassar ( , 2000cNassar ( , 2002f, 2004b on wild Manihot species and focuses on different topics reviewed by us recently.…”

Review Apomixis in cassava: advances and challenges

“…In this case, additional chromosomes in the aneuploid F 2 plant (2n = 38) have allowed for homozygosity and dosages necessary for the action of these genes. The connection between apomixis and aneuploidy was confirmed in more recent research (Nassar, 2002(Nassar, , 2003bNassar et al, 2000Nassar et al, , 2009). …”

Breeding Vegetatively Propagated Crops

“…Polyploidy and apoximis could participate in the evolution of cassava within the genus Manihot. Polyploidy enhances genetic variation, whereas the apomictic mechanism, which appears to be favored by natural selection, offers an escape from lethality and provides a means for perpetuating the genotype (Nassar, 2001b). Sexual polyploidization occurs in cassava because of 2n gametes, and some polyploid cassava genotypes show high plant vigor during growth and root yield (Hahn et al, 1990).…”