Development of co-dominant SCAR markers linked to resistant gene against the Fusarium oxysporum f. sp. radicis-lycopersici

Major Soilborne Pathogens of Field Processing Tomatoes and Management Strategies

Globally, tomato is the second most cultivated vegetable crop next to potato, preferentially grown in temperate climates. Processing tomatoes are generally produced in field conditions, in which soilborne pathogens have serious impacts on tomato yield and quality by causing diseases of the tomato root system. Major processing tomato-producing countries have documented soilborne diseases caused by a variety of pathogens including bacteria, fungi, nematodes, and oomycetes, which are of economic importance and may threaten food security. Recent field surveys in the Australian processing tomato industry showed that plant growth and yield were significantly affected by soilborne pathogens, especially Fusarium oxysporum and Pythium species. Globally, different management methods have been used to control diseases such as the use of resistant tomato cultivars, the application of fungicides, and biological control. Among these methods, biocontrol has received increasing attention due to its high efficiency, target-specificity, sustainability and public acceptance. The application of biocontrol is a mix of different strategies, such as applying antagonistic microorganisms to the field, and using the beneficial metabolites synthesized by these microorganisms. This review provides a broad review of the major soilborne fungal/oomycete pathogens of the field processing tomato industry affecting major global producers, the traditional and biological management practices for the control of the pathogens, and the various strategies of the biological control for tomato soilborne diseases. The advantages and disadvantages of the management strategies are discussed, and highlighted is the importance of biological control in managing the diseases in field processing tomatoes under the pressure of global climate change.

Phylogenetic relationship among Indian population of Fusarium oxysporum f. sp. lentis infecting lentil and development of specific SCAR markers for detection

The present study was taken up to understand the phylogenetic relationship using ITS and TEF markers among 22 isolates of Fusarium oxysporum f. sp. lentis (Fol) causing lentil wilt belonging to eight races isolated from different geographic locations of India and to develop specific markers for its detection. The nucleotide sequences of ITS region varied from 490 to 560 bp whereas, 670-725 bp for TEF 1α. The phylogeny analysis revealed that the isolates were more than 98% similar based on the neighbour joining analysis and were grouped into two major clusters in both ITS and TEF. The first major cluster of ITS had twenty isolates whereas for TEF, there were 15 isolates. Two sets of SCAR markers MS1 (162 bp) and MS2 (125 bp) were designed and synthesised. These markers were used against race representative Fol isolates for amplification. While, MS 1 marker was able to detect the genomic DNA up to 0.1 ng, MS 2 could detect the Fol genomic DNA up to 0.05 ng. The specificity of these two markers to detect Fol and their inability to amplify most common lentil pathogens (Rhizoctonia solani, R. bataticola, Sclerotium rolfsii, Sclerotinia sclerotiarum, and Aschochyta rabiei) makes them a reliable tool for detection. The phylogenetic analysis is helpful in the understanding of variability in Fol populations and the SCAR markers help in rapid and reliable detection of an important pathogen of lentil.

Identifying molecular markers suitable for Frl selection in tomato breeding

Modern plant breeding heavily relies on the use of molecular markers. In recent years, next generation sequencing (NGS) emerged as a powerful technology to discover DNA sequence polymorphisms and generate molecular markers very rapidly and cost effectively, accelerating the plant breeding programmes. A single dominant locus, Frl, in tomato provides resistance to the fungal pathogen Fusarium oxysporum f. sp. radicis-lycopersici (FORL), causative agent of Fusarium crown and root rot. In this study, we describe the generation of molecular markers associated with the Frl locus. An F₂ mapping population between an FORL resistant and a susceptible cultivar was generated. NGS technology was then used to sequence the genomes of a susceptible and a resistant parent as well the genomes of bulked resistant and susceptible F₂ lines. We zoomed into the Frl locus and mapped the locus to a 900 kb interval on chromosome 9. Polymorphic single-nucleotide polymorphisms (SNPs) within the interval were identified and markers co-segregating with the resistant phenotype were generated. Some of these markers were tested successfully with commercial tomato varieties indicating that they can be used for marker-assisted selection in large-scale breeding programmes.

Development of a high-resolution melting marker for selecting Fusarium crown and root rot resistance in tomato

Fusarium crown and root rot is a severe fungal disease of tomato caused by Fusarium oxysporum f. sp. radicis-lycopersici (FORL). In this study, the genomic location of the FORL-resistance locus was determined using a set of molecular markers on chromosome 9 and an F2 population derived from FORL-resistant inbred ‘AV107-4’ (Solanum lycopersicum) × susceptible ‘L3708’ (Solanum pimpinellifolium). Bioassay performed using Korean FORL strain KACC 40031 showed single dominant inheritance of FORL resistance in the F2 population. In all, 13 polymerase chain reaction-based markers encompassing approximately 3.6–72.0 Mb of chromosome 9 were developed based on the Tomato-EXPEN 2000 map and SolCAP Tomato single nucleotide polymorphism array analysis. These markers were genotyped on 345 F2 plants, and the FORL-resistance locus was found to be present on a pericentromeric region of suppressed chromosomal recombination in chromosome 9. The location of the FORL-resistance locus was further confirmed by testing these markers against diverse commercial tomato and stock cultivars resistant to FORL. A restriction fragment length polymorphism marker, PNU-D4, located at approximately 6.1 Mb of chromosome 9 showed the highest match with the resistance locus and was used for conducting high-resolution melting analysis for marker-assisted selection of FORL resistance.