Robert W. Stack

Head blighting potential of Fusarium species associated with spring wheat heads

Seven Fusarium species isolated from spring wheat heads were tested for pathogenicity. Only F. graminearum and F. culmorum caused severe blighting of wheat heads following inoculation in the greenhouse. F. tricincium, F. sporotrichioides, F. equiseti, F. acuminalum, and F. poae did not blight heads but sometimes caused damage to inoculated spikelets.

Molecular cytogenetic characterization of four partial wheat-Thinopyrum ponticum amphiploids and their reactions to Fusarium head blight, tan spot, and Stagonospora nodorum blotch

Four wheat (Triticum aestivum L.)-Thinopyrum ponticum derivatives SS5 (PI604926), SS156 (PI604947), SS363 (PI604970), and SS660 (PI604879), were identified as resistant to Fusarium head blight (FHB), a serious fungal disease of wheat worldwide. Seedling reactions to tan spot and Stagonospora nodorum blotch (SNB), two important foliar diseases of wheat, suggest that these four derivatives are resistant to tan spot and two of them (SS5 and SS156) are resistant to SNB. Fluorescent genomic in situ hybridization (FGISH) patterns of mitotic chromosomes indicate that these four derivatives are partial wheat-Th. ponticum amphiploids, each with a total of 56 chromosomes, though with different amounts of Th. ponticum chromatin. These four amphiploids were hybridized with each other to determine homology between the Th. ponticum genomes in each of the amphiploids. Analysis of chromosome pairing in the F1 hybrids using FGISH suggests that each amphiploid carries a similar set of Th. ponticum chromosomes. These wheat-Th. ponticum amphiploids represent a potential novel source of resistance to FHB, tan spot, and SNB for wheat breeding.

Homoeology of Thinopyrum junceum and Elymus rectisetus chromosomes to wheat and disease resistance conferred by the Thinopyrum and Elymus chromosomes in wheat

Thirteen common wheat “Chinese Spring” (CS)-Thinopyrum junceum addition lines and three common wheat “Fukuhokomuji”(Fuku)-Elymus rectisetus addition lines were characterized and verified as disomic additions of a Th. junceum or E. rectisetus chromosome in the wheat backgrounds by fluorescent genomic in situ hybridization. Another Fuku-E. rectisetus addition line, A1048, was found to contain multiple segregating E. rectisetus chromosomes. Seven partial CS-Th. junceum amphiploids were identified to combine 12–16 Th. junceum chromosomes with CS wheat chromosomes. The disomic addition lines AJDAj5, 7, 8, 9, and HD3508 were identified to contain a Th. junceum chromosome in homoeologous group 1. Two of them, AJDAj7 and AJDAj9, had the same Th. junceum chromosome. AJDAj2, 3, and 4 contained a Th. junceum chromosome in group 2, HD3505 in group 4, AJDAj6 and AJDAj11 in group 5, and AJDAj1 probably in group 6. The disomic addition lines A1026 and A1057 were identified to carry an E. rectisetus chromosome in group 1 and A1034 in group 5. E. rectisetus chromosomes in groups 1–6 were detected in A1048. The homoeologous group of the Th. junceum chromosome in HD3515 could not be determined in this study. Several Th. junceum and E. rectisetus chromosomes in the addition lines were found to contain genes for resistance to Fusarium head blight, tan spot, Stagonospora nodorum blotch, and stem rust (Ug99 races). Understanding of the homoeology of the Th. junceum and E. rectisetus chromosomes with wheat will facilitate utilization of the favorable genes on these alien chromosomes in wheat improvement.

Colonization of potato by Rhizoctonia solani as affected by crop rotation

Potato stems and stolons infected with Rhizoctonia solani Kuhn were collected from ten fields in the Red River Valley of North Dakota, USA, in 1987. Six potato cultivars were sampled from dryland production areas with different crop rotation schemes. Approximately 1350 isolations from 203 plants were made for the recovery of R. solani. Pure cultures of R. solani were obtained and 119 cultures were successfully purified using a hyphal tip technique. These cultures were paired on anastomosis plates with tester isolates representing anastomosis groups AG-1 through AG-9, and tested for pathogenicity on potato. Anastomosis groups 4 and 5 were the predominant groups recovered from potato plants sampled in fields not previously cropped to potato, while anastomosis groups 3 and 5 were most frequently recovered from fields with a previous cropping history of potato. The potato plants grown in these fields also had the highest incidence of symptoms and greatest severity. There was no relationship between potato cultivar and the colonization of a particular anastomosis group of R. solani. Based on these preliminary studies, infection of potato by various anastomosis groups of R. solani appears to be influenced mainly by crop rotation in our production area.

Breeding Hard Red Spring Wheat for FusariumHead Blight Resistance

Fusarium head blight (FHB) or scab (caused by Fusarium graminearum Schwabe [telomorph Gibberella zeae (Schwein.) Petch]) is one of the most destructive diseases of wheat (Triticum aestivum L.) worldwide, causing significant reductions in grain yield and quality. In the USA, since the 1993 FHB epidemic, tremendous research efforts have been undertaken to address this major problem that causes substantial economic losses for the wheat growers, industry, and export market. The deployment of resistant varieties is the only effective, economical and environmentally safe way to control FHB in wheat. More than a decade of classical breeding efforts to develop scab resistant hard red spring wheat (HRSW) cultivars at North Dakota State University (NDSU) resulted in releasing several HRSW cultivars with varying levels of FHB resistance. Since 2000, three major HRSW cultivars with FHB resistance were released and grown on large scale in the Northern-Central plains of the USA. These are ‘Alsen’ (2000), ‘Steele-ND’ (2004), and ‘Glenn’ (2005). Alsen has been grown, in average, on more than one million hectares in the last 3 years. However, Alsen and most FHB resistant wheat cultivars released by other wheat programs in the USA, trace back to the Chinese line ‘Sumai-3’ (PI481542) or its derivatives. The HRSW breeding program at NDSU has invested substantial breeding efforts to identify, introgress novel resistance genes from other sources to enhance genetic diversity, and facilitate pyramiding these resistance genes. The ultimate objective is developing HRSW cultivars with effective and durable FHB resistance. Our efforts have yielded in releasing the HRSW cultivars ‘‘Steele-ND’’ in 2004 and ‘‘Glenn’’ in 2005. Steele-ND traces its resistance to the wheat relative species Triticum dicoccoides and Glenn combines both Alsen and Steele-ND resistances. This paper addresses the breeding efforts at NDSU to release FHB resistant HRSW cultivars and elite germplasm as parental material for many breeding programs worldwide; and the future challenges to keep our research efforts ahead of the FHB disease