Curly top in sugar beet continues to be a challenging disease to control in the western United States. To aid in development of host resistance and management options, the curtovirus species composition was investigated by sampling 246 commercial fields along with nursery and field trials in the western United States. DNA was isolated from leaf samples and the species were identified using species-specific polymerase chain reaction primers for the C1 gene. Amplicons from 79 isolates were also sequenced to confirm identifications. Beet severe curly top virus (BSCTV) and Beet mild curly top virus (BMCTV) were widely distributed throughout the western United States, while only a few isolates of Beet curly top virus (BCTV) were found. In phylogenetic analysis, BSCTV, BMCTV, and BCTV isolates formed distinct groups in the dendrogram. Seven isolates not amplifiable with species-specific primers did amplify with curly top coat protein primers, indicating novel curtovirus species or strains may be present. Given the wide host range of the viruses responsible for curly top, frequent co-infections, and genetic diversity within and among species, establishing better host resistance, and controlling curly top will continue to be a challenge.

Root diseases of wheat and barley in southeastern Idaho (Intermountain West area of the U.S.A.) have not been extensively studied. Surveys were conducted in 2001 and 2002 to assess root disease severity and to identify soilborne pathogens present in 81 wheat and 52 barley fields in 13 southeastern Idaho counties. Bipolaris sorokiniana and Fusarium culmorum were the most frequent pathogens isolated and also the most virulent in greenhouse pathogenicity tests. Other pathogenic fungi isolated from root lesions included Fusarium spp., Rhizoctonia solani, and Gaeumannomyces graminis var. tritici. Nematode soil assays revealed that 96% of the fields had lesion nematodes (mostly Pratylenchus neglectus) and 78% had stunt nematodes (Tylenchorhynchus spp.). Other nematode species were detected in less than 18% of the fields. The cereal cyst nematode (Heterodera avenae) was found in two fields. Greenhouse experiments with soil cores indicated that disturbing the soil to simulate disking reduced the severity of fusarium root rot. Plant breeders attempting to incorporate resistance to root rot into cereal crops in the Intermountain West should focus on screening with B. sorokiniana and F. culmorum isolates.

Rhizoctonia root rot causes serious losses on sugar beet worldwide. In order to help explain why Rhizoctonia root rot management practices have not performed well in some areas of the Intermountain West (IMW), a survey was conducted. In the IMW from 2004 to 2006, 94 Rhizoctonia solani field isolates were collected from sugar beet roots. These field isolates were compared with 19 reference strains and 46 accessions from GenBank for genetic diversity based on sequencing of the ITS-5.8S rDNA region. Greenhouse pathogenicity tests on sugar beet and silage corn were conducted and plant damage was assessed using a randomized complete block design with at least four replications. The majority of the isolates had sequence identity with the AG-2-2 IIIB (47%) or AG-4 subgroups (44%). Most of the AG-2-2 isolates (87%) were associated with fields in the western portion of the production area, while 71% of the AG-4 isolates came from the eastern portion of the production area. Isolates from AG-2-2 IIIB were frequently more virulent on sugar beet and sequence of the ITS-5.8s region required cloning because of genetic diversity within isolates. Seven (all AG-2-2 IIIB) of 18 isolates tested could attack both sugar beet and corn, while two of the seven virulent isolates caused less root rot on corn. To reduce Rhizoctonia root rot on sugar beet and corn, crop rotations and the isolates utilized for selecting host resistance could be given further consideration.