Wild cassava, Manihot spp.: Biology and potentialities for genetic improvement

Abstract

Wild species of Manihot are progenitors of cassava. They constitute valuable genetic reservoirs presenting genes that show new characters. Screening of these species showed some of them to have a notably high percentage of protein combined with a low percentage of hydrocyanic acid. Study of natural habitats revealed resistance to drought and excessive soil aluminum toxicity as well as adaptation to low temperature. Some of the hybrids obtained showed high root productivity and resistance to stem borers. Apomixis was discovered in the wild and transferred successfully to the cultivate species.*Dedicated to Clibas Vieira, a tireless student of crop improvement on his 70th anniversary.

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

“…Central Brazil (southern Goiás and eastern Minas Gerais) is home to the largest Manihot diversity (38 of the 98 accepted species), whereas Mexico, the second largest center of diversity, harbors 17 Manihot species (Nassar, 1978a(Nassar, , 2000c. The third largest center of diversity is northeast Brazil with 16 species, whereas there are six species in south Mato Grosso and Bolivia that together are the fourth center of Manihot diversity.…”

“…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).…”

“…(Nassar, 1978a(Nassar, , 1985 shallowly stellate (Nassar, 1982). Hybridizes with frequently 5 lobed, sometimes cassava in nature (Nassar, 2000c …”

“…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.…”

First report of Uromyces carthagenensis on Manihot grahamii (Euphorbiaceae) in Uruguay

“…The genus Manihot (Euphorbiaceae) contains around 100 species which are native to the Neotropical region (Rogers and Appan 1973) with Central Brazil having the richest diversity (Nassar 2000). Manihot species are found mostly in dry regions and vary in habitat from small trees to shrubs (Rogers and Appan 1973).…”