Abstract
Cassava brown streak disease (CBSD) is currently the major disease affecting cassava production in Eastern and Southern Africa. Breeding for resistance has been hampered by a lack of sources of resistance and the complexity of CBSD. This study was initiated to assess the possibility of exploiting inbreeding, as a strategy for generating new sources of resistance to CBSD. This was based on the premise that inbreeding increases the additive variance upon which selection for desirable phenotypes can be made. Eight cassava progenitors (S0): Namikonga, 182/006661, Kigoma Red, Tz/130, Tz/140, 130040, 0040 and 100142 were selfed for one generation to produce the first inbred generation (S1). The S1 progenies generated were evaluated for two seasons (seedling and clonal evaluation trial) in a high CBSD pressure area. Promising clones were re-evaluated to confirm their CBSD reaction status. Results obtained showed that within each family, a few S1 inbreds (1-15) had higher levels of resistance compared to the S0 progenitors with the highest number observed in Tz/130. It is possible therefore to get transgressive progenies through inbreeding. Key words: Cassava brown streak disease, inbreeding, cassava partial inbreds, new sources of resistance, inbreeding depression, resistance breeding.
Highlights
Cassava (Manihot esculenta Crantz.) is one of the most important root crops grown widely in tropical countries notably in sub-Saharan Africa, South America and Asia
The disease is caused by two virus species, cassava brown streak virus (CBSV) and Uganda cassava brown streak virus (UCBSV), both are Ipomoviruses of family Potyviridae characterized by an elongate flexuous filament 650 to 690 nm long (Monger et al, 2001; Mbanzibwa et al, 2011)
Due to high heterozygosity of cassava as a crop, it had been hypothesized that a low rate of germination would be obtained due to inbreeding depression
Summary
Cassava (Manihot esculenta Crantz.) is one of the most important root crops grown widely in tropical countries notably in sub-Saharan Africa, South America and Asia. Cassava brown streak disease (CBSD) is the major disease affecting cassava production in Eastern and Southern Africa (Pennisi, 2010). CBSD and a lack of natural resistance has posed a great challenge to breeding efforts tailored towards increasing cassava productivity in CBSD affected areas. These viruses are distributed in Tanzania (Ndunguru et al, 2015), Kenya (Munga, 2008), Uganda (Alicai et al, 2007), Democratic Republic of Congo (Mulimbi et al, 2012), Rwanda (Tomlinson et al, 2013), Burundi (Bigirimana et al, 2011), Malawi (Mbewe et al, 2015) and Mozambique (Zacarias and Labuschagne, 2010). Undocumented reports of CBSD outbreaks in Zambia have been made
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