Utility of indirect and direct selection traits for improving Striga resistance in two sorghum recombinant inbred populations

Abstract

Breeding of sorghum (Sorghum bicolor L. Moench) for resistance to the parasitic weed Striga hermonthica (Del.) Benth. has been hampered by the difficulty of evaluating host resistance in the field and lack of reliable screening techniques. Therefore, we investigated the value of various indirect and direct measures of Striga resistance as selection traits. Two sorghum recombinant inbred populations of 226 F 3:5 lines each were developed from the crosses (1) IS 9830  E 36-1 and (2) N 13  E 36-1. Strigaresistant line IS 9830 is characterized by low stimulation of Striga seed germination, whereas Striga-susceptible line E 36-1 produces germination stimulants in abundance. Line N 13 possesses ''mechanical'' resistance and probably also an antibiosis mechanism. Resistance was assessed in 1997 and 1998 using in vitro agar-gel assays with Striga seeds from Kenya, Mali, and Niger, pot trials in the respective three countries, and field experiments in Kenya and Mali. The agar-gel assay proved to be a useful, precise and fast indirect selection method to screen for sorghum entries with the low-stimulant character. However, correlation analysis showed that this resistance mechanism was ineffective in some environments, especially in Kenya, pointing to the necessity of field evaluation. Because of low heritability estimates and moderate to low correlations to Striga resistance under field conditions, pot screening appeared to be of limited use in breeding programs. The field trials confirmed the effectiveness of several direct measures of Striga resistance in sorghum: emerged Striga counts, Striga severity index, and area under the Striga number or severity progress curves. A two-row plot field layout with an empty row between plots, coupled with artificial infestation of test rows, lattice design and six replications offered an improved screening procedure that achieved high heritability. Significant genotype  environment interactions in the field experiments stress the importance of multi-locational trials to achieve stable Striga resistance.

Prospects for an integrated control of Loranthaceae species parasitizing <em>Vitellaria paradoxa</em> C. F. Gaertn in Burkina Faso

“…The same observation was made on the resistance mechanism of some cereal cultivars in Striga controlling (Kuiper et al, 1998). The existence of differences in cultivar susceptibility against Striga hermonthica has been highlighted among sorghum cultivars (Omanya et al, 2004;Rodenburg et al, 2006) and maize (Zea mays L.) cultivars (Kim et al, 1998). Our results confirmed that of Hariri (1990) and Dibong et al (2009) from their experiments on artificial infestations with other species of Loranthaceae.…”

Characterization of host tolerance to Striga hermonthica

“…Many different selection measures have been developed for resistance. All of these measures are based on the number of aboveground Striga plants and vary from a single count at a specific moment in time (Adetimirin et al, 2000a;Omanya et al, 2004) or the maximum number of aboveground Striga plants (Wilson et al, 2000(Wilson et al, , 2004Rodenburg et al, 2005) to the area under the Striga number progress curve (ASNPC) (Adetimirin et al, 2000a;Haussmann et al, 2000;Wilson et al, 2000Wilson et al, , 2004Omanya et al, 2004;Rodenburg et al, 2005). Complete resistance, also referred to as immunity against Striga, has not yet been found.…”

Striga

“…Where a potential host plant defense is expressed, it can be narrowed to a specific stage in the parasite life cycle. This has been made possible through the development and extensive exploitation of advanced laboratory-based bioassays, which have provided weed researchers with fine phenotyping tools Ejeta, 2007;Omanya et al 2004). Based on the knowledge gained, it has been suggested that the overall expression of resistance to the parasites can be broken down into two major parts, pre-attachment and post-attachment, in the establishment of the parasitic association.…”

“…Research effort invested to characterize the mechanisms behind and inheritance of resistance to Striga has been followed by the development of molecular markers. Recently, mapping of chromosomal regions affecting qualitative or quantitative traits has received growing attention in millets Ejeta and Butler, 1993;Haussmann et al, 2001a;Omanya et al, 2004;Rich et al, 2004;Mohamed et al, 2003;Kountche, 2013;Moumouni et al, 2015). In sorghum, several populations segregating for genes associated with low germination stimulant production (lgs), low haustorial initiation, mechanical barriers, hypersensitive response, and incompatible response mechanisms of Striga resistance have been developed using the source materials (Ejeta et al, 2000;Haussmann et al, 2000;Grenier et al, 2001Grenier et al, , 2007Rodenburg et al, 2006;Omanya et al, 2004;Mutengwa et al, 2005).…”

“…Relatively few cultivars with good level of Striga resistance have been identified in millet crops, mainly sorghum and pearl millet Kountche et al, 2013). Improved breeding approaches that promise good prospects for developing cultivars with resistance to Striga have been suggested to take advantage of the ever-growing knowledge of the complex nature of the host-parasite interactions Haussmann et al, 2000;Omanya et al 2004). Adoption of these strategies has resulted in the development of appropriate breeding populations, and deployment of deliberate selection for resistance to Striga.…”