parasite and its hosts. Empirical breeding for striga resistance in field crops has relied on selection of host plants Availability of appropriate laboratory procedures that reveal the that allow emergence of few parasitic plants and show specific interactions between the parasitic striga (Striga spp.) and host genotypes in the early stages of infection facilitates characterization little or no loss in productivity of the crop. Sorghum of the specific mechanisms of resistance. Our objective was to use an in genotypes with good levels of striga resistance have been vitro extended agar gel assay (EAGA) to characterize hypersensitive identified using this approach. However, the specific response (HR) to parasitic invasion of sorghum [Sorghum bicolor mechanisms of many of these resistance sources have (L.) Moench] genotypes. The HR was characterized by expression of not been determined. Nevertheless, there appears to be necrotic lesions at the haustorial attachment sites which discouraged a general parallel between host-pathogen interactions further penetration of the parasite into host roots. We examined the in plant diseases and defense responses triggered during HR reaction of seven cultivated, five wild, and 95 BC 3 F 4 genotypes striga invasion. The major limitation to making a precise derived from a wild resistant (P47121) and two susceptible male sterile determination of these observations during the developbased populations ( CK60 and KP9). The susceptible genotypes ment of the parasite appears to be the lack of approshowed no necrosis. In contrast, resistant cultivars Framida and Dobbs, and a wild accession, P47121, showed necrosis in Ͼ67% of

Striga hermonthica (Del.) Benth. is the major biotic constraint to sorghum production. Its control is difficult and can only be achieved through integrated management strategies that depend mainly on host plant resistance and enhanced soil fertility. However, breeding for resistance is hampered by the complexity of host parasite interactions and lack of reliable screening methods. The invention of molecular markers has enhanced the effectiveness of breeding for resistance. Five genomic regions (QTLs) with linked markers associated with Striga resistance were mapped in sorghum variety N13 by [10]. In this study, to increase the efficiency of marker-assisted selection (MAS), 27 EST-SSR markers in close association with Striga resistance QTLs were also identified and mapped. Populations of backcross (BC 3 S 4 ) derived from N13 (Striga resistant) X three farmer preferred sorghum cultivars: Tabat, Wad Ahmed and AG-8 (Striga susceptible) were generated. Thirty-one lines (BC 3 S 4 ) with confirmed Striga field resistance were genotyped with foreground and background selection makers. Twenty resistant lines, with two or more major QTLs were selected for regional evaluation. Of these 10 lines were selected and advanced for multi-location testing, together with Wad Ahmed, Tabat, AG-8, N13, SRN39 and IS9830 as checks. Standard variety trials were conducted in Striga sick plots over three seasons (2009)(2010)(2011) in Sudan, Gezira Research Station, Damazine, Sinnar, and Gedarif. Results revealed that four lines (T1BC 3 S 4 , AG6BC 3 S 4 , AG2BC 3 S 4 and W2BC 3 S 4 ) were Striga resistant and agronomically superior with yields ranging from 180% to 298% higher relative to their recurrent parents. This Striga resistance coupled with superior attributes of the recurrent parent (including very high yield potentials, high grain quality and drought tolerance) will provide adaptation and stability across a wide range of environments. These are the first products of DNA markerassisted selection (MAS) in sorghum released for cultivation by farmers in sub-Saharan Africa.

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Witchweed (Strigas spp.) is one of the most important cereals production constraints globally and is projected to worsen with anticipated climate change. It is especially a devastating parasitic weed in Sub-Saharan Africa and parts of Asia. Integrated management strategies that depend mainly on host plant resistance provide the most effective control mechanism for Striga. We used molecular marker-assisted backcrossing to introgress Striga resistance from a resistant genotype, N13, into agronomically important genetic backgrounds (Tabat and Wad Ahmed). Backcross populations BC3S3 were generated and genotyped using Simple Sequence Repeat (SSR) and Diversity Arrays Technology (DArT) markers. A total of 17 promising backcross progenies were selected and screened in Striga infested field alongside their parents. The Area Under Striga Progress Curve (AUSPC) showed significant decrease in Striga count (920-7.5) resulting in a 97-189% increase in yield under Striga pressure. Our results demonstrate the practical application of marker assisted selection (MAS) to generate farmer-preferrd Striga resistant lines in Sudan.

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Conditioned seeds of Striga asiatica (L.) Kuntze release ethylene, which elicits germination. We investigated the activity of 1‐aminocyclopropane‐1‐carboxylate (ACC) oxidase and respiration during conditioning. Seeds incubated in vivo with ACC, the substrate for ACC oxidase, produced negligible ethylene at the beginning of conditioning or if they were dormant (i.e. would not germinate after conditioning and treatment with stimulant). Non‐dormant seeds produced 3000 ηL of ethylene/600 seeds/24 h after 12 days of conditioning. In vitro ACC oxidase activity at day 0 of conditioning produced 500 ηL of ethylene/μg protein/h and 8000 ηL of ethylene/μg protein/h after 12 days of conditioning. Incubation of seeds in strigol before protein extraction did not enhance enzyme activity. Seeds released 4000 μL/L CO2 in the first 24 h of conditioning, with the rate increasing to 15 000 μL/L/24 h on day 4 and then remaining roughly unchanged. Maximum in vitro activity of ACC oxidase required ACC, catalase, O2, Fe2+, ascorbate and CO2. In vivo activity of ACC oxidase required ACC and/or germination stimulant(s), suggesting that stimulants may be involved in providing substrates for the ACC oxidase. No difference was observed in the separation of extracted proteins, which suggests that ACC oxidase is activated during conditioning, perhaps as a result of changes in co‐factor concentration. Application of these findings to Striga control is discussed.

Among the biotic stresses affecting dryland cereals, especially sorghum, Striga hermonthica is the most damaging obligate parasite, and is an important bottleneck to yield increases by smallholder farm ers, yet it has been neglected by research in recent years. Integrated Striga management packages have been designed, but these will continue to require new cultural and chemical treatments, resistant vari eties, and integrated approaches to manage both Striga and soil fertility. This review attempts to assess recent advances in bioassay development that are specific to resistance mechanisms, genomics such as New Generation Sequencing tools, RNA interference (RNAi) technologies in advancing knowledge of resistance and susceptibility to Striga including diversity in striga populations, and molecular marker technology in accelerating the development o f Sm ga-resistant cultivars of sorghum. Recent advances in developing effective bioassays involving several modifications of rhizotrons and sand-packed titer plate assay will help dissect resistance mechanisms into component traits and increased understanding of the specific resistance mechanisms, which will directly help in efficient introgression and selection of several striga resistance mechanisms in breeding population. The current studies for identification of parasite genes specifically involved in haustorigenesis through transcriptomic and/or prote'omic stud ies and more recently RNAseq studies will help understand susceptibility or resistance genes in striga. Release o f improved version of cultivars resistant to striga developed by marker-assisted backcrossing of several striga resistance QTLs in Sudan had shown the power of integrating genomics and molecular breeding tools/techniques into routine breeding for tackling the complex constraint such as striga. A p plication and utilization of advance techniques in genomics and molecular breeding appropriately can further enhance the efficiency o f integrated striga management practices, and thus crop productivity.