Molecular tagging and validation of microsatellite markers linked to the low germination stimulant gene (lgs) for Striga resistance in sorghum [Sorghum bicolor (L.) Moench]

Abstract

Striga is a devastating parasitic weed in Africa and parts of Asia. Low Striga germination stimulant activity, a well-known resistance mechanism in sorghum, is controlled by a single recessive gene (lgs). Molecular markers linked to the lgs gene can accelerate development of Striga-resistant cultivars. Using a high density linkage map constructed with 367 markers (DArT and SSRs) and an in vitro assay for germination stimulant activity towards Striga asiatica in 354 recombinant inbred lines derived from SRN39 (low stimulant) × Shanqui Red (high stimulant), we precisely tagged and mapped the lgs gene on SBI-05 between two tightly linked microsatellite markers SB3344 and SB3352 at a distance of 0.5 and 1.5 cM, respectively. The fine-mapped lgs region was delimited to a 5.8 cM interval with the closest three markers SB3344, SB3346 and SB3343 positioned at 0.5, 0.7 and 0.9 cM, respectively. We validated tightly linked markers in a set of 23 diverse sorghum accessions, most of which were known to be Striga resistant, by genotyping and phenotyping for germination stimulant activity towards both S. asiatica and S. hermonthica. The markers co-segregated with Striga germination stimulant activity in 21 of the 23 tested lines. The lgs locus similarly affected germination stimulant activity for both Striga species. The identified markers would be useful in marker-assisted selection for introgressing this trait into susceptible sorghum cultivars. Examination of the sorghum genome sequence and comparative analysis with the rice genome suggests some candidate genes in the fine-mapped region (400 kb) that may affect strigolactone biosynthesis or exudation. This work should form a foundation for map-based cloning of the lgs gene and aid in elucidation of an exact mechanism for resistance based on low Striga germination stimulant activity.

Mutation in sorghum LOW GERMINATION STIMULANT 1 alters strigolactones and causes Striga resistance

“…Informative recombinants from the RIL population used to fine-map the LGS1 locus (20) were further genotyped and their SLs phenotyped by ultraperformance liquid chromatography tandem mass spectrometry (UPLC-MS-MS) with comparison with standards as previously described (32). In addition to these, four low-stimulant lines (555, IS7777, SC103, and Tetron) with reported Striga field resistance and their hybrids with SRN39 were used to establish allelic relationships of lgs1 mutants and verify the identity of LGS1 from among the gene candidates.…”

“…The Striga-resistant sorghum variety SRN39 carrying this mutation was mated with a Chinese landrace Shanqui Red, with high germination stimulant activity, to generate a genetic mapping population of 600 recombinant inbred lines (RILs). In a previous genotypic and phenotypic evaluation of 328 RILs by the agar gel assay we created a genetic map with 428 markers, placing the LGS1 (LOW GERMINATION STIMULANT 1) locus in a region near the tip of chromosome 5 with fine mapping that delimited it to a 30-gene region (20).…”

Ecological relevance of strigolactones in nutrient uptake and other abiotic stresses, and in plant-microbe interactions below-ground

“…Indeed, it was shown that the low SL producing tomato mutants Sl-ORT1 and high pigment-2 (hp-2 dg ) are more resistant to infection by different Orobanche and Phelipanche species than the corresponding wild-types (Dor et al 2011b;López-Ráez et al 2008b). Genetic variation for low SL production has also been described in other important crops such as sorghum, rice and faba bean (Dor et al 2011b;Fernández-Aparicio et al 2014;Jamil et al 2011b;López-Ráez et al 2008b;Satish et al 2012). In sorghum, this genetic variation was used to breed for Striga resistant varieties for use in Africa (Ejeta 2007).…”

Striga

“…Haussmann et al (2004) mapped several QTLs for Striga resistance in sorghum and reported 9 and 11 QTLs explaining respectively 77% and 82% of the phenotypic variation in a recombinant inbred line (RIL) population. The most significant QTL has been identified to correspond to the major gene locus lgs, which was recently fine-mapped on the chromosome 5 (Satish et al, 2012). More interestingly, validation of some of these QTLs has provided an opportunity to employ molecular marker-assisted breeding (MAB) for sorghum improvement for Striga resistance.…”