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Sesame (Sesamum indicum L.) is one of the most important oilseed crops. Accurate and efficient means to identify each variety of sesame are needed for improvement of the sesame production market. In this study, three kinds of molecular markers were used for DNA fingerprinting of 151 sesame cultivars released in China since 1960: single nucleotide polymorphisms (SNPs), insertions or deletions (InDels), and simple sequence repeats (SSRs). The 140 polymorphic markers used (47 SNPs, 47 InDels, and 46 SSRs) revealed a narrow range of genetic variation among the 151 Chinese sesame cultivars. Clustering analysis classified them into three main groups, which were consistent with the cultivars' geographical distribution. Three of the 151 cultivars (AH03, AH04, and AH05 from the Anhui Province) were considered synonymous cultivars because of their high genetic similarity coefficients ( > 98%). Overall, 15 SNPs, 14 InDels, and 9 SSRs were sufficient to distinguish all sesame cultivars and the DNA fingerprints generated from these markers allowed establishing two-dimensional graphical barcodes to accurately and rapidly identify sesame cultivars. Thus, we have provided a useful protocol for the identification and authentication of various sesame cultivars and revealed the usefulness of SNPs, InDels, and SSRs in cultivar identification and intellectual property protection; the fingerprinting codes obtained for the 151 sesame cultivars should be useful in sesame breeding and marketing seed. [ABSTRACT FROM AUTHOR]

Sesame Fusarium wilt (SFW), caused by Fusarium oxysporum f. sp. sesami (Fos), is one of the most devastating diseases affecting sesame cultivation. Deciphering the genetic control of SFW resistance is pivotal for effective disease management in sesame. An inheritance study on a cross between the highly resistant variety Yuzhi 11 and the highly susceptible accession Sp1 using a Fos pathogenicity group 1 isolate indicated that resistance was conferred by a single dominant allele. The target locus was located in a 1.24 Mb interval on chromosome 3 using a combination of cross-population association mapping and bulked segregant analysis. Fine genetic mapping further narrowed the interval between 21,350 and 21,401 kb. The locus Sindi_0812400 was identified as the SFW resistance gene and officially designated SiRLK1. This gene encodes a specific malectin/receptor-like protein kinase with three putative tandem kinase domains and is considered a kinase fusion protein. Sequence analysis revealed that a high proportion (49.44%) of variants within the locus was located within the kinase domain III, and several of which were evidently associated with the diversity in SFW response, indicating the critical role of kinase domain III in expression of disease resistance. These findings provide valuable information for further functional analysis of SFW resistance genes and marker-assisted resistance breeding in sesame. [ABSTRACT FROM AUTHOR]

Fusarium wilt is a common fungal disease in sesame caused by Fusarium oxysporum f. sp. sesami (FOS). To determine the toxin production profiles of the FOS isolates with different pathogenicity levels under various culture conditions, we assessed the content variation of fusaric acid (FA) and 9, 10-dehydrofusaric acid (9, 10- DFA) produced by the four representative FOS isolates. Results indicated that the concentration of FA reached to a maximum of 2848.66 μg/mL in Czapek medium, while 9, 10-DFA was mainly produced in Richard and Lowcarbon Richard medium. The concentration of 9, 10-DFA on Richard culture medium varied from 0 μg/mL to 716.89 μg/mL. Of the five culture media used in this study, Czapek culture medium was the most conductive to produce FA. FA production was significantly affected by culture medium, culture time, and their interactions. Results suggest that there is no correlation between toxin production and pathogenicity level of FOS isolates. These findings provide key information for the mechanism analysis of FOS- sesame interaction and pathogen control. [ABSTRACT FROM AUTHOR]

Background: Sesame (Sesamum indicum L.) is one of the most important oil crops; however, a lack of useful molecular markers hinders current genetic research. We performed transcriptome sequencing of samples from different sesame growth and developmental stages, and mining of genic-SSR markers to identify valuable markers for sesame molecular genetics research. Results: In this study, 75 bp and 100 bp paired-end RNA-seq was used to sequence 24 cDNA libraries, and 42,566 uni-transcripts were assembled from more than 260 million filtered reads. The total length of uni-transcript sequences was 47.99 Mb, and 7,324 SSRs (SSRs ≥15 bp) and 4,440 SSRs (SSRs ≥?18 bp) were identified. On average, there was one genic-SSR per 6.55 kb (SSRs ≥15 bp) or 10.81 kb (SSRs ≥18 bp). Among perfect SSRs (≥18 bp), di-nucleotide motifs (48.01%) were the most abundant, followed by tri- (20.96%), hexa- (25.37%), penta- (2.97%), tetra- (2.12%), and mono-nucleotides (0.57%). The top four motif repeats were (AG/CT)n [1,268 (34.51%)], (CA/TG)n [281 (7.65%)], (AT/AT)n [215 (5.85%)], and (GAA/TTC)n [131 (3.57%)]. A total of 2,164 SSR primer pairs were identified in the 4,440 SSR-containing sequences (≥18 bp), and 300 SSR primer pairs were randomly chosen for validation. These SSR markers were amplified and validated in 25 sesame accessions (24 cultivated accessions, one wild species). 276 (92.0%) primer pairs yielded PCR amplification products in 24 cultivars. Thirty two primer pairs (11.59%) exhibited polymorphisms. Moreover, 203 primer pairs (67.67%) yielded PCR amplicons in the wild accession and 167 (60.51%) were polymorphic between species. A UPGMA dendrogram based on genetic similarity coefficients showed that the correlation between genotype and geographical source was low and that the genetic basis of sesame in China is narrow, as previously reported. The 32 polymorphic primer pairs were validated using an F2 mapping population; 18 primer pairs exhibited polymorphisms between the parents, and 14 genic-SSRs could be integrated into 9 main linkage groups. Conclusions: 2,164 genic-SSR markers have been developed in sesame using transcriptome sequencing. 276 of 300 validated primer pairs successfully yielded PCR amplicons in 24 cultivated sesame accessions. These markers increase current SSR marker resources and will greatly benefit genetic diversity, qualitative and quantitative trait mapping and marker-assisted selection studies in sesame. [ABSTRACT FROM AUTHOR]

Fusarium oxysporum f. sp. sesami is an extremely destructive pathogen, causing sesame Fusarium wilt disease worldwide. To clarify the pathogenicity and the genetic characters of F. oxysporum f. sp. sesami, we systematically investigated 69 F. oxysporum isolates collected from major sesame-growing areas in China. Among these isolates, 54 isolates were pathogenic and 15 were nonpathogenic according to pathogenicity testing on sesame seedlings. For the pathogenic isolates, three F. oxysporum f. sp. sesami pathogenicity groups were defined based on the three differential sesame hosts for the first time. A translation elongation factor 1a gene tree was constructed to determine the genetic diversity of the F. oxysporum isolates but could not separate F. oxysporum f. sp. sesami isolates from the nonpathogenic isolates and other F. oxysporum formae speciales. Ten secreted-in-xylem (SIX) genes (one family of effectors) were identified in F. oxysporum f. sp. sesami isolates by a search with the genome data, and were subsequently screened in the 69 F. oxysporum isolates. Compared with the SIX gene profiles in other F. oxysporum formae speciales, the presence and sequence variations of the SIX gene homologs directly correlated with the specific pathogenicity of F. oxysporum f. sp. sesami toward sesame. Furthermore, eight of these F. oxysporum f. sp. sesami SIX genes were significantly expressed in sesame plants as infection of the F. oxysporum f. sp. sesami isolate. These findings have important significance for understanding the pathogenic basis of F. oxysporum f. sp. sesami isolates, and will contribute to improve the diagnostics to effectively control Fusarium wilt disease in sesame. [ABSTRACT FROM AUTHOR]