Horizontal resistance: core to a research breakthrough to combat Striga in Africa

Abstract

The parasitic flowering plants, Striga species, represent the largest biological constraint to cereal and legume crop production in sub-Saharan Africa. Eighty-three percent of Striga worldwide (35 species) occurs in Africa. Among them, Striga hermonthica causes the greatest damage. The IITA's scientists began research on breeding maize for horizontal resistance to Striga in 1982. By 1995 a comprehensive approach to combat Striga on maize had been developed and demonstrated. This included the development of a simple field infestation technique, the discovery of durable resistance genes, genetic studies of resistance genes and the formation of many resistant varieties (hybrids and synthetics) with high grain quality, high grain and stover yields and a combined resistance to major biotic and abiotic stresses. Multilocation testing and subsequent seed multiplication of the resistant varieties was carried out by national programmes in Benin, Burkina Faso, Cameroon, the Ivory Coast, Ethiopia, Ghana, Nigeria, and Togo. Striga-resistant maize varieties show horizontal resistance not only to S. hermonthica, but also to another species, Striga asiatica. Based on the results of a 15year research, an integrated approach using resistant varieties and cereal-legume intercropping or rotation is recommended as a sustainable and permanent solution to combat Striga in Africa. This horizontal resistance package, with a combined resistance to other biotic stresses, could be applicable not only to Striga problems in other crops such as sorghum, millet, rice and cowpea, but also to other parasitic weeds, such as Orobanche species. This paper reviews and discusses why, approximately a century's research work on parasitic weeds, has not led to a major research breakthrough.

Inheritance of Tolerance of Maize Inbreds to Exserohilum turcicum in North Korea

“…in Africa (Nigeria and Zimbabwe) and Asia (Thaialand) (S. K. Kim, unpublished) cannot sustain the durability of resistance. Tolerance, general or partial resistance must be pursued (Kim, 1993a(Kim, , 1993b(Kim, , 1994a(Kim, , 1994b(Kim, , 1996. However, scientists of many developing countries still look for un-durable race-specific single gene controlled of high resistance (Kim, 2000).…”

“…If any one side is over-dominates the other, mutation of a new biotype occurs naturally for their survival. The senior author called the tolerance and durable resistance approach of crop breeding the Genetic IPM (Integrated Pest Management) (Kim, 1996(Kim, , 2000. A crop cultivar that co-survives with pests in nature confers very powerful effects comparing to the high resistance, chemical spray, and other method of control.…”

“…For environmentally friendly green food production, the host tolerance is the key for the crop stability and durability. Others presented this principle as horizontal resistance or race non-specific (Singh et al, 2004), durable resistance (Zadoks, 1993), general resistance (Brewbaker, 1983), generalized resistance (Hooker and Kim, 1973), race-non specific resistance (Nelson, 1973), partial resistance (Carson and Van Dyke, 1994;Pataky, 1994), quantitative resistance and QTL resistance (Kim, 1996(Kim, , 2000Kim et al, 2008).…”

“…However, this accumulation needs extra efforts in breeding. Uses of stable tolerance genes across races can be simpler and more durable (Kim 1996;Kim 2000).…”

Tolerance Expression of Maize Genotypes to Exserohilum turcicum in North and South Korea

“…Numerous examples of the breakdown of a single gene for high resistance have been reported with other biotic stresses including Puccinia sorghi Brewbaker 1976, 1977), P. polysora (Brewbaker et al, 2011;Kim 1993;Kim et al, 1988), B. maydis (Kim et al, 1988), maize streak virus (Kim et al, 1989), and Striga hermonthica (Kim 1994a;Kim 1994b;Kim 1996). The importance of quantitatively inherited genes for tolerance against diseases, parasitic weeds, and insects has been studied by many groups in details (Brewbaker 1974;Brewbaker et al, 1990Brewbaker et al, , 2011Carson and Van Dyke, 1994;Kim 1993Kim , 2002Nelson 1973;Pataky 1994;Robinson 1996;Van der Plank 1968;Zadocks 1993).…”