Document Type

Thesis - University Access Only

Award Date

2001

Degree Name

Doctor of Philosophy (PhD)

Department / School

Agronomy

Abstract

Wheat streak mosaic virus (WSMV) (Family: Potyviridae; Genus: Tritimovirus) is a major threat for wheat (Triticum aestivum L. em. Thell.) in the Great Plains region of the USA and many other wheat producing areas of the world. While WSMV evaluation and improvement of tolerance is an important objective of wheat breeding programs, little information is known on the tolerance of winter wheat cultivars to WSMV infection in South Dakota and the Great Plains region and on the genetics controlling WSMV tolerance in winter wheat. The objectives of this study were to (i) evaluate the winter wheat genotypes grown in South Dakota Advanced Yield Trials (A YT) and Crop Performance Trials (CPT) for their tolerance to WSMV, (ii) determine the combining abilities for WSMV tolerance in winter wheat using parents of known differential reactions to the virus, and (iii) determine the mode of inheritance and the type of gene action of WSMV tolerance in winter wheat. Fifty winte~ wheat genotypes ( experimental lines and released cultivars) grown in South Dakota A YT and CPT were used in the evaluation of winter wheat genotypes for their tolerance to WSMV in greenhouse and field conditions. Nine parents were chosen for the diallel study (combining abilities) based on the diversity of origin and the level of tolerance to WSMV from the previous screening tests. One line resistant to WSMV (OK65C93-8) and two susceptible lines (Tandem and Vista) were used for the inheritance study. The first study was conducted in both greenhouse and field for two years (1996-1997 and 1997-1998) while the second and third studies were conducted in the greenhouse in 1999-2000 and 2000-2001, respectively. Plants were inoculated with WSMV-SD isolate and healthy plants were used as control. For the first study in the greenhouse, the analysis of variance showed that differences among genotypes, persons, and rating times were highly significant (P < 0.01). There was no significant genotype X person X rating time, indicating consistency in genotype response to WSMV assessed by the three different individual raters over a period of four times. Based on the least significant difference value (LSD= 0.58) over two years, Dawn and Jagger were among nine genotypes which were classified as tolerant to WSMV while Roughrider and Vista were among the genotypes classified as susceptible to WSMV. For the field study, highly significant differences (P < 0.01) were found among genotypes for grain yield, test weight, kernel weight, plant height, number of seed per head, days to heading and disease symptoms. High significance (P < 0.01) was also observed between treatments (healthy and infected) for the same plant characteristics previously mentioned except for kernel weight, seeds per kernel, and ELISA values. No significant differences were observed in reduction of all characters as indicated by _the lack of significance of genotype X treatment interaction, which might have been caused by environmental conditions. Even though the reductions of the previously mentioned plant characteristics were not significant, Dawn and Jagger appeared to have the lowest reduction in grain yield and yield components. Phenotypic correlation between greenhouse and field disease rating was significant (r = 0.27; P < 0.05), indicating that greenhouse disease rating could be used as an additional mean of identifying winter wheat cultivars tolerant to WSMV in the field or vice versa. For the diallel study, the analysis of variance revealed that highly significant (P < 0.01) differences existed for the general combining ability (GCA) and specific combining ability (SCA). There were no significant differences for the reciprocals, indicating the absence of maternal effects. The GCA effects were higher than the SCA effects, indicating that additive gene effects largely control the inheritance of WSMV tolerance in the plant material that was used. For the study of the mode of inheritance and the type of gene action for WSMV tolerance in winter wheat, the chi-square analysis revealed that one pair of a single recessive gene and two gene pairs with dominant and recessive epistasis control the resistance to WSMV. The generation means analysis showed that additive genetic variance is present and predominant in some genetic materials, indicating that selection for WSMV tolerance in the early generations should be effective. The heritability estimates showed that WSMV resistance is a heritable trait due the high values of both narrow and broad-sense heritabilies. The results obtained from these studies indicated that a good level of tolerance to WSMV exists in some winter wheat cultivars commercially grown in South Dakota and therefore, they should be deployed in breeding programs to serve as source of tolerance to WSMV. Additive, dominance, and epistatic effects are all involved in the inheritance ofWSMV resistance. The high heritability estimates associated with important additive genetic variance found in this study demonstrate that considerable progress may be expected from selection for WSMV resistance in segregating winter wheat populations.

Library of Congress Subject Headings

Wheat streak mosaic virus
Winter wheat -- Disease and pest resistance

Format

application/pdf

Number of Pages

149

Publisher

South Dakota State University

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