Development of a New DNA Marker for Fusarium Yellows Resistance in Brassica rapa Vegetables

In vegetables of Brassica rapa L., Fusarium oxysporum f. sp. rapae (For) or F. oxysporum f. sp. conglutinans (Foc) cause Fusarium yellows. A resistance gene against Foc (FocBr1) has been identified, and deletion of this gene results in susceptibility (focbr1-1). In contrast, a resistance gene against For has not been identified. Inoculation tests showed that lines resistant to Foc were also resistant to For, and lines susceptible to Foc were susceptible to For. However, prediction of disease resistance by a dominant DNA marker on FocBr1 (Bra012688m) was not associated with disease resistance of For in some komatsuna lines using an inoculation test. QTL-seq using four F2 populations derived from For susceptible and resistant lines showed one causative locus on chromosome A03, which covers FocBr1. Comparison of the amino acid sequence of FocBr1 between susceptible and resistant alleles (FocBr1 and FocBo1) showed that six amino acid differences were specific to susceptible lines. The presence and absence of FocBr1 is consistent with For resistance in F2 populations. These results indicate that FocBr1 is essential for For resistance, and changed amino acid sequences result in susceptibility to For. This susceptible allele is termed focbr1-2, and a new DNA marker (focbr1-2m) for detection of the focbr1-2 allele was developed.

Pseudmonas cannabina pv. alisalensis TrpA Is Required for Virulence in Multiple Host Plants

Pseudomonas cannabina pv. alisalensis (Pcal) causes bacterial leaf spot and blight of Brassicaceae and Poaceae. We previously identified several potential Pcal virulence factors with transposon mutagenesis. Among these a trpA mutant disrupted the tryptophan synthase alpha chain, and had an effect on disease symptom development and bacterial multiplication. To assess the importance of TrpA in Pcal virulence, we characterized the trpA mutant based on inoculation test and Pcal gene expression profiles. The trpA mutant showed reduced virulence when dip- and syringe-inoculated on cabbage and oat. Moreover, epiphytic bacterial populations of the trpA mutant were also reduced compared to the wild-type (WT). These results suggest that TrpA contributes to bacterial multiplication on the leaf surface and in the apoplast, and disease development. Additionally, several Brassicaceae (including Japanese radish, broccoli, and Chinese cabbage) also exhibited reduced symptom development when inoculated with the trpA mutant. Moreover, trpA disruption led to downregulation of bacterial virulence genes, including type three effectors (T3Es) and the phytotoxin coronatine (COR), and to upregulation of tryptophan biosynthesis genes. These results indicate that a trade-off between virulence factor production and Pcal multiplication with tryptophan might be regulated in the infection processes.

Transposon mutagenesis reveals Pseudomonas cannabina pv. alisalensis optimizes its virulence factors for pathogenicity on different hosts

Pseudomonas cannabina pv. alisalensis (Pcal), which causes bacterial blight disease of Brassicaceae, is an economically important pathogen worldwide. To identify Pcal genes involved in pathogenesis, we conducted a screen for 1,040 individual Pcal KB211 Tn5 mutants with reduced virulence on cabbage plants using a dip-inoculation method. We isolated 53 reduced virulence mutants and identified several potential virulence factors involved in Pcal virulence mechanisms such as the type III secretion system, membrane transporters, transcription factors, and amino acid metabolism. Importantly, Pcal is pathogenic on a range of monocotyledonous and dicotyledonous plants. Therefore, we also carried out the inoculation test on oat plants, which are cultivated after cabbage cultivation as green manure crops. Interestingly among the 53 mutants, 31 mutants also exhibited reduced virulence on oat seedlings, indicating that Pcal optimizes its virulence factors for pathogenicity on different host plants. Our results highlight the importance of revealing the virulence factors for each plant host-bacterial interaction, and will provide new insights into Pcal virulence mechanisms.

Variability in Chickpea Rot-causing Soil-borne Necrotrophs, Sclerotiumrolfsii and Macrophominaphaseolina

The present work was designed to identify the cultural and pathogenic variability of the two chickpea rot-causing necrotrophicsoil-borne pathogens i.e. Sclerotiumrolfsii and Macrophominaphaseolinacause significant damage to chickpea cultivation.The potentiality of the isolates for infection was recognized with artificial inoculation test using susceptible genotypes. Disease index values of S. rolfsii and M. phaseolina were 24.9–68.8% and 20.0–64.0%, respectively. Among twelve isolates of S. rolfsii, BAUSr4 and Ag2 produced the highest infection on genotype L550 (cd: 10.79). Likewise, isolate DarkMP4J followed by DarkMP1J and Jute1, among twenty–one isolates of M. phaseolina, rendered maximum infection on genotype K850 (cd: 5.15). No relationship was established among the cultural characters and pathogenicity of the isolates. Isolates differed in aggressiveness across different locations and hosts.

Varian efikasi penularan tungro oleh koloni-koloni wereng hijau Nephotettix virescens distant

Green leafhopper-resistant variety is one of rice tungro virus disease control measure. Green leafhopper (GLH), Nephotettix virescens is the most efficient vector of tungro. Among 7 sources of resistant gene to GLH 4 genes have been employed to breed resistant variety. Efficiency variant of GLH as indicated by their efficiency to transfer tungro virus was identified by inoculation test. GLH colonies were collected from tungro endemic areas in Java, Bali, West Nusa and South Sulawesi. Efficiency variant of GLH colony was characterized by their ability to transfer tungro virus to GLH-resistant variety with various source of resistant genes. Sources of tungro inoculum were obtained in Bogor. The results of the test showed that there was a variation in the ability of GLH colonies to tranfer tungro to various GLH-resistant variety, thus indicate there was a variant in GLH colony. The ability of GLH colonies to transfer virus ranked from high to low, were West Nusa Tenggara, Bali, East Java , South Sulawesi, D.I. Yogyakarta, West Java and Central Java. On the other hand GLH-resistant variety ranked from resistant to susceptible were varieties with resistant genes group glh4, Glh6, Glh1 and Glh5. Five variants colonies of GLH were successfully identified which named as colony 0050, 0000, 1050, 1650 and 1654. Biotype 0000 has the lowest ability to transfer virus but biotype 1654 efficiently transfer virus to all of GLH-resistant variety groups.