Isolation and molecular analysis of R-gene in resistant Zingiber officinale (ginger) varieties against Fusarium oxysporum f.sp. zingiberi

Benzalkonium Chloride and Benzethonium Chloride Effectively Reduce Spore Germination of Ginger Soft Rot Pathogens: Fusarium solani and Fusarium oxysporum

Ginger soft rot is a serious soil-borne disease caused by Fusarium solani and Fusarium oxysporum, resulting in reduced crop yields. The application of common chemical fungicides is considered to be an effective method of sterilization, and therefore, they pose a serious threat to the environment and human health due to their high toxicity. Benzalkonium chloride (BAC) and benzethonium chloride (BEC) are two popular quaternary ammonium salts with a wide range of fungicidal effects. In this study, we investigated the fungicidal effects of BAC and BEC on soft rot disease of ginger as alternatives to common chemical fungicides. Two soft rot pathogens of ginger were successfully isolated from diseased ginger by using the spread plate method and sequenced as F. solani and F. oxysporum using the high-throughput fungal sequencing method. We investigated the fungicidal effects of BAC and BEC on F. solani and F. oxysporum, and we explored the antifungal mechanisms. Almost complete inactivation of spores of F. solani and F. oxysporum was observed at 100 mg/L fungicide concentration. Only a small amount of spore regrowth was observed after the inactivation treatment of spores of F. solani and F. oxysporum in soil, which proved that BAC and BEC have the potential to be used as an alternative to common chemical fungicides for soil disinfection of diseased ginger.

Plant defense response against Fusarium oxysporum and strategies to develop tolerant genotypes in banana

Soil-borne fungal pathogen, Fusarium oxysporum causes major economic losses by inducing necrosis and wilting symptoms in many crop plants. Management of fusarium wilt is achieved mainly by the use of chemical fungicides which affect the soil health and their efficiency is often limited by pathogenic variability. Hence understanding the nature of interaction between pathogen and host may help to select and improve better cultivars. Current research evidences highlight the role of oxidative burst and antioxidant enzymes indicating that ROS act as an important signaling molecule in banana defense response against Fusarium oxysporum f.sp. cubense. The role of jasmonic acid signaling in plant defense against necrotrophic pathogens is well recognized. But recent studies show that the role of salicylic acid is complex and ambiguous against necrotrophic pathogens like Fusarium oxysporum, leading to many intriguing questions about its relationship between other signaling compounds. In case of banana, a major challenge is to identify specific receptors for effector proteins like SIX proteins and also the components of various signal transduction pathways. Significant progress has been made to uncover the role of defense genes but is limited to only model plants such as Arabidopsis and tomato. Keeping this in view, we review the host response, pathogen diversity, current understanding of biochemical and molecular changes that occur during host and pathogen interaction. Developing resistant cultivars through mutation, breeding, transgenic and cisgenic approaches have been discussed. This would help us to understand host defenses against Fusarium oxysporum and to formulate strategies to develop tolerant cultivars.

Isolation and characterization of nucleotide-binding site resistance gene homologues in common bean (Phaseolus vulgaris)

Common bean production is constrained by many fungal, viral, and bacterial pathogens. Thus, the identification of resistance (R) genes is an important focal point of common bean research. The main goal of our study was to identify resistance gene homologues (RGH) in the crop, using degenerate primers designed from conserved sequences in the nucleotide-binding site (NBS) domains of R-genes from the model legume Medicago truncatula. Total DNA of the Andean common bean genotype G19833 was used for amplification of over 500 primer combinations. Sequencing of amplicons showed that 403 cloned fragments had uninterrupted open reading frames and were considered representative of functional RGH genes. The sequences were grouped at two levels of nucleotide identity (90 and 80%) and representative sequences of each group were used for phylogenetic analyses. The RGH sequence diversity of common bean was divided into TIR and non-TIR families, each with different clusters. The TIR sequences grouped into 14 clades while non-TIR sequences grouped into seven clades. Pairwise comparisons showed purifying selection, although some sequences may have been the result of diversifying selection. Knowledge about RGH genes in common bean can allow the design of molecular markers for pyramiding of resistance genes against various pathogens.

Identification and evaluation of two diagnostic markers linked to Fusarium wilt resistance (race 4) in banana (Musa spp.)

Fusarium wilt caused by the fungus Fusarium oxysporum f. sp. cubense race 4 (FOC4) results in vascular tissue damage and ultimately death of banana (Musa spp.) plants. Somaclonal variants of in vitro micropropagated banana can hamper success in propagation of genotypes resistant to FOC4. Early identification of FOC4 resistance in micropropagated banana plantlets is difficult, however. In this study, we identified sequence-characterized amplified region (SCAR) markers of banana associated with resistance to FOC4. Using pooled DNA from resistant or susceptible genotypes and 500 arbitrary 10-mer oligonucleotide primers, 24 random amplified polymorphic DNA (RAPD) products were identified. Two of these RAPD markers were successfully converted to SCAR markers, called ScaU1001 (GenBank accession number HQ613949) and ScaS0901 (GenBank accession number HQ613950). ScaS0901 and ScaU1001 could be amplified in FOC4-resistant banana genotypes ("Williams 8818-1" and Goldfinger), but not in five tested banana cultivars susceptible to FOC4. The two SCAR markers were then used to identify a somaclonal variant of the genotype "Williams 8818-1", which lost resistance to FOC4. Hence, the identified SCAR markers can be applied for a rapid quality control of FOC4-resistant banana plantlets immediately after the in vitro micropropagation stage. Furthermore, ScaU1001 and ScaS0901 will facilitate marker-assisted selection of new banana cultivars resistant to FOC4.

R proteins as fundamentals of plant innate immunity

Plants are attacked by a wide spectrum of pathogens, being the targets of viruses, bacteria, fungi, protozoa, nematodes and insects. Over the course of their evolution, plants have developed numerous defense mechanisms including the chemical and physical barriers that are constitutive elements of plant cell responses locally and/or systemically. However, the modern approach in plant sciences focuses on the evolution and role of plant protein receptors corresponding to specific pathogen effectors. The recognition of an invader's molecules could be in most cases a prerequisite sine qua non for plant survival. Although the predicted three-dimensional structure of plant resistance proteins (R) is based on research on their animal homologs, advanced technologies in molecular biology and bioinformatics tools enable the investigation or prediction of interaction mechanisms for specific receptors with pathogen effectors. Most of the identified R proteins belong to the NBS-LRR family. The presence of other domains (including the TIR domain) apart from NBS and LRR is fundamental for the classification of R proteins into subclasses. Recently discovered additional domains (e.g. WRKY) of R proteins allowed the examination of their localization in plant cells and the role they play in signal transduction during the plant resistance response to biotic stress factors. This review focuses on the current state of knowledge about the NBS-LRR family of plant R proteins: their structure, function and evolution, and the role they play in plant innate immunity.

Identification and molecular mapping of a Fusarium wilt resistant gene in upland cotton

Fusarium wilt (FW) is one of the most economically damaging cotton diseases worldwide, causing yellowing, wilting, defoliation, vascular tissue damage and ultimately death. Identification of molecular markers linked to FW genes is vital to incorporate resistance into elite cotton cultivars. An intraspecific F(2) in Gossypium hirsutum L. was developed by crossing with a highly resistant cultivar Zhongmiansuo 35 (ZMS35) and a susceptible cultivar Junmian 1 to screen simple sequence repeats (SSRs) closely linked to the FW resistance gene. FW was identified in F(2:3) families by evaluating seedling leaf symptoms and vascular tissue damage at plant maturity under natural field infection conditions over 2 years. The results showed that FW resistance segregated in a 3:1 ratio as a simple monogenic trait in F(2:3) families. Molecular mapping identified a FW resistance gene closely linked with the SSR marker JESPR304(-280) in chromosome D3(c17). We proposed to name this gene FW ( R ). A composite interval mapping method detected four QTLs for FW resistance in Chr.A7(c7), D1(c15), D9(c23) and D3, respectively. Among them, one major QTL (LOD > 20) was tagged near marker JESPR304 within an interval of 0.06-0.2 cM, and explained over 52.5-60.9% of the total phenotypic variance. The data confirmed the existence of a major gene in Chr.D3. This is the first report of molecular mapping of a major gene contributing FW resistance in cotton. The present research therefore provides an opportunity to understand the genetic control of resistance to FW and conduct molecular marker-assisted selection breeding to develop FW resistant cultivars.