A novel form of resistance in rice to the angiosperm parasite Striga hermonthica

Abstract

Summary• The root hemiparasitic weed Striga hermonthica is a serious constraint to grain production of economically important cereals in sub-Saharan Africa. Breeding for parasite resistance in cereals is widely recognized as the most sustainable form of long-term control; however, advances have been limited owing to a lack of cereal germplasm demonstrating postattachment resistance to Striga .• Here, we identify a cultivar of rice (Nipponbare) that exhibits strong postattachment resistance to S. hermonthica ; the parasite penetrates the host root cortex but does not form parasite-host xylem-xylem connections.• In order to identify the genomic regions contributing to this resistance, a mapping population of backcross inbred lines between the resistant (Nipponbare) and susceptible (Kasalath) parents were evaluated for resistance to S. hermonthica .• Composite interval mapping located seven putative quantitative trait loci (QTL) explaining 31% of the overall phenotypic variance; a second, independent, screen confirmed four of these QTL. Relative to the parental lines, allelic substitutions at these QTL altered the phenotype by at least 0.5 of a phenotypic standard deviation. Thus, they should be regarded as major genes and are likely to be useful in breeding programmes to enhance host resistance.

Striga

“…Some potential resistant host plants have been reported to lack the capacity to stimulate haustorial initiation of Striga germinated seeds or to produce compounds that inhibits the formation of the haustorium, an important organ towards parasite connection to host root (Gurney et al, 2003;Rich et al, 2004;Robert, 2011). Several authors demonstrated also the establishment of mechanical barriers to protect the host root from parasite penetration and access to the host plant vascular system (Maiti et al, 1984;Gurney et al, 2006;Amusan et al, 2008;Yoshida and Shirasu, 2009). Another protecting mechanism is the recognition of the invasion as a threat and the rapid mobilization of defense response such as the hypersensitive response (HR).…”

“…Over the past decades, research efforts have led to the discovery of new sources of resistance to Striga in several host crops including millets and other cereals (Lane et al, 1997;Gurney et al, 2003;Karaya et al, 2012;Wilson et al, 2000Wilson et al, , 2004Gurney et al, 2006;Amusan et al, 2008;Cissoko et al, 2011). In sorghum, several cultivars and breeding lines have been reported to be resistant and/or tolerant to Striga Rodenburg et al 2006;Ejeta, 2007).…”

“…The search for resistance or tolerance often begins by the recognition of plants around which fewer or less vigorous Striga plants are observed or the crop yield is less affected relative to other plants growing around them in fields deliberately infested with parasitic weed seeds. This was followed by the development of several screening, including both field and laboratory, methods that allow the assessment of plant germplasm towards characterization for their reaction to Striga Gurney et al 2006;Mohamed et al, 2010;Amusan et al, 2011). The power and advantage of the laboratory-based approach is that it pushes the limit of what would traditionally (identified under field conditions) be considered good source for resistance to Striga.…”

“…The latter is complex, intimately associated with that of the host and to the climate, particularly during post-ripening (Hearne, 2009). Striga plants have a high reproductive capacity: a single plant can produce 100000 to 200000 very tiny (0.15 ~ 0.30 mm in diameter) seeds, which are easily dispersible (Parker and Riches, 1993;Gurney et al, 2006;Hearne, 2009). Striga seeds require a period of pre-treatment, conditioning in a moist warm environment (30°C in germination bioassays) for 2 to 16 days before they acquire potential to germinate (Longan and Stewart, 1991;Parker and Riches, 1993).…”

“…Striga infest millets, such as sorghum, pearl millet, finger millet, foxtail millet, little millet, proso millet, fonio, teff and barnyard millet (Chemisquy et al, 2010;Olivier, 1995;Parker, 2012;Atera et al, 2012), which represent the staple food and fodder crops of millions of poor rural families in the tropical and semi-arid regions of their cultivation, therefore are of utmost significance to subsistence farmers. Millets thus play a critical role in ensuring food security in these regions Senthilvel et al, 2008 (Gurney et al, 2003(Gurney et al, , 2006Elzein and Kroschel, 2004;Vasey et al, 2005;Amusan et al, 2008). Indeed, Striga are the major and persistent biotic threat to production of these crops mostly grown on the hottest and driest marginal regions of sub-Saharan Africa, Middle East and large part of Asia (Gurney et al, 2002;Gressel et al, 2004;Ejeta, 2007;Rispail et al, 2007;Scholes and Press, 2008;Parker, 2012).…”