Virulence of Pythium Species Isolated from Wheat Fields in Eastern Washington

Abstract

Although Pythium root rot in wheat (Triticum aestivum) is well documented, limited information is available concerning which species of Pythium are most responsible for disease damage. The objective of this study was to examine the variation in virulence on wheat among isolates of Pythium collected from cereal grain fields in eastern Washington. Isolates of nine Pythium species were tested for virulence on spring wheat cultivars Chinese Spring and Spillman. Cultivars were planted in pasteurized soil infested with Pythium isolates and placed in a growth chamber maintained at a constant 16°C and ambient humidity. Plant height, length of the first true leaf, and number of seminal roots were recorded, and roots were digitally scanned to create computer files that were analyzed using WinRhizo software. Pythium isolates caused a significant reduction (P < 0.05) in the number of root tips, root length, and length of the first leaf. Differences in virulence were detected among species and among isolates within species. Isolate Pythium debaryanum 90136 and P. ultimum 90038 were the most virulent and may prove useful in future disease screening assays of Triticum germ plasm.

Evaluation of Adapted Wheat Cultivars for Tolerance to Pythium Root Rot

“…Variation in virulence of P. debaryanum and P. ultimum also was detected. For every variable measured, P. ultimum caused greater effects on measured variables when compared with the controls than did P. debaryanum, which agrees with previous results (14). Similarly, Chamswarng and Cook (2) and Ingram and Cook (15) found P. ultimum to be among the most pathogenic of the Pythium spp.…”

“…Germ plasm used in this study included both experimental breeding lines and commercially released varieties (Table 1), and for simplicity, all germ plasm will be referred to as genotypes. Based on results from a previous virulence assay (14), P. ultimum isolate 90038 and P. debaryanum isolate 90136 were chosen for use in disease screening assays.…”

“…have been reported on wheat in North America (11). From a sample of 80 wheat fields in eastern Washington, Paulitz and Adams (22) found 46 combinations of 13 different Pythium spp., and nine of these were virulent on wheat (14).…”

Low Input No-till Cereal Production in the Pacific Northwest of the U.S.: The Challenges of Root Diseases

“…A greenhouse bioassay was developed using small pine seedling containers and pasteurized soil inoculated with a soil-rolled oat inoculum of Pythium spp. Among Pythium species, P. ultimum and P. debaryanum (later identified as P. irregulare group IV), were the most virulent species (Higginbotham et al, 2004a). Pythium ultimum and P. debaryanum were then used to screen a collection of spring wheat lines from the U.S., and three lines were found to have a reproducibly higher level of tolerance (Higgingbotham et al, 2004b).…”

Metalaxyl-M-Resistant Pythium Species in Potato Production Areas of the Pacific Northwest of the U.S.A.

“…In the Pacific Northwest (PNW; Idaho, Oregon and Washington), potatoes are rotated with a diverse array of crops including: peas, carrots, corn, beans, onions and cereals that are susceptible to Pythium seed and seedling rot (Higginbotham et al 2004;Kraft and Burke 1971;Pscheidt and Ocamb 2007;Paulitz and Adams 2003;Broders et al 2007; Davis and Nunez 1999;Sumner et al 1997;Hendrix and Campbell 1973). The systemic fungicide metalaxyl-M is commonly used as a foliar or in-furrow application to manage Pythium leak and pink rot on potato, cavity spot on carrot, and as a seed treatment to manage Pythium preemergence damping off on most vegetable seed and cereal crops grown in crop rotation with potato in the PNW (Pscheidt and Ocamb 2007).…”