Identification of Powdery Mildew Pathogen and Ribosomal DNA-ITS Sequence Analysis on Melon

Identification of powdery mildew pathogens on melon（Cucumis melo） is important for melon breeding and diseaseresistant germplasm selection. In this study, a powdery mildew pathogen that infected melon plants in Heilongjiang Province, China, was investigated in terms of host identification, morphological characteristics and phylogenetic relationships. The morphological characteristics of the pathogen were observed at five phases in the life cycle： germinating conidia, primary germ tube, hyphae, conidiophores, and colonization. The conidia were elliptical, colorless, catenulate, and the average length was 29.07 μm and average width was 17.82 μm. One ascus and eight ascospores were produced. DNA was extracted from 0.01 g conidiophores from a strain of powdery mildew pathogen that infected melon. ITS ribosomal DNA region（524 bp） was amplified with the universal ITS1 and ITS4 primers. The nucleotide sequence showed 100% similarity with ITS sequences for three Podosphaera fusca strains obtained from the GenBank database. The identity of the pathogen was confirmed as Sphaerotheca fuliginea. International standard differential hosts were used to identify S. fuliginea strain as 2F race. These results supported the notion that Podosphaera fusca was a synonym of S. fuliginea.

Isolation and Identification of Fusarium Wilt Pathogens from Bitter Gourd in Hainan Province

In order to isolate and identify the pathogens causing Fusarium wilt in bitter gourd in Hainan Province, China, four bitter gourd plants exhibiting symptoms of Fusarium wilt were collected from Tunchang County, Hainan Province. Four pathogen strains （HNTC-01, HNTC-02, HNTC-03 and HNTC-04） were isolated from the four plants, and identified via morphological observation and molecular techniques. The results showed that HNTC--01, HNTC-03 and HNTC-04 were F. oxysporum, while HNTC-02 was F. graminearum. The tests on pathogenicity and host specificity showed that HNTC-01, HNTC-03 and HNTC-04 were F. oxysporum Schl. f. sp. momordicae. Phylogenetic analysis revealed that HNTC-01, HNTC-03, HNTC-04 were clustered together with 14 strains of F. oxysporum, and HNTC-02 was clustered together with six strains of F. graminearum. In addition, rDNA-ITS region can be used to distinguish different Fusarium species, but can not be used to distinguish different biotypes within a Fusarium species. This study could provide a scientific basis for the diagnosis and prevention of wilt in bitter gourd.

Host status of Brachypodium distachyon to the cereal cyst nematode

Cereal cyst nematode（Heterodera avenae, CCN） distributes worldwide and has caused severe damage to cereal crops, and a model host will greatly aid in the study of this nematode. In this research, we assessed the sensitivity of 25 inbred lines of Brachypodium distachyon to H. avenae from Beijing, China. All lines of B. distachyon were infested by secondstage juveniles（J2s） of H. avenae from Daxing District of Beijing population, but only 13 inbred lines reproduced 0.2–3 cysts/plant, showing resistance. The entire root system of the infested B. distachyon appeared smaller and the fibrous roots were shorter and less numerous. We found that a dose of 1 000 J2s of H. avenae was sufficient for nematode infestation. We showed that Koz-1 of B. distachyon could reproduce more cysts than TR2A line. Line Koz-1 also supported the complete life cycles of 5 CCN geographical populations belonging to the Ha1 or Ha3 pathotype group. Our results suggest that B. distachyon is a host for CCN.