Zhongxian Wu

Document Type

Thesis - University Access Only

Award Date

1996

Degree Name

Master of Science (MS)

Department / School

Plant Science

First Advisor

Marie A.C. Langham

Abstract

Wheat streak mosaic virus (WSMV) causes wheat streak mosaic which is a serious threat to wheat production. This study dealt with WSMV titer variations over time in winter wheat plants, among eight winter wheat genotypes reported to have different responses to WSMV, and among different plant parts of four winter wheat genotypes. In all studies, the effects of WSMV on vegetative growth during the early growth stage was measured. All research was done under greenhouse conditions, and the relative WSMV concentration was measured with protein-A enzyme-linked immunosorbent assay (PA-ELISA). During early growth, symptoms developed at a steady rate in the two cultivars and reached maximum by 30 days post-inoculation (DPI) when ELISA absorbance values from shoots and roots had already peaked and begun to decline. Protein-A ELISA detection of WSMV in shoots and roots coincided with the onset of symptom development (6 DPI). Virus titers in shoots and roots measured by ELISA exhibited cyclic changes, increasing to peak values at 21 DPI in shoots and at 18 DPI in roots. Values then decreased at 24 DPI and finally increased at 27 and 30 DPI in both shoots and roots. Shoot weights and root weights were significantly reduced by WSMV at 30 DPI. Growth rates of shoots and roots in infected plants were always lower than control plants, but were not significant at all cases. Correlation coefficients for ELISA values and fresh weights indicated the growth of shoots and roots at an early stage was affected by each other as well as influenced by WSMV infection. Symptom ratings of the eight genotypes ranged from 2.7 to 4.3 and were not always consistent with previously reported responses. Shoot and root ELISA absorbance values in infected plants of all genotypes tested positive when compared with control plants, ranging from 0.861-1.266 and 0.100-0.482 in absorbance, respectively. Values of ELISA from infected roots were consistently lower than those from infected shoots. Shoot weights from five genotypes (Arapahoe, Arlin, Rawhide, Vista KS93WGRC 27), root weights from all genotypes (Arapahoe, Arlin, Pronghorn, NE89526, Rawhide, Redland, Vista and KS93WGRC27) and root/shoot ratios from seven genotypes (Arapahoe, Arlin, Pronghorn, NE89526, Redland, Vista and KS93WGRC 27) were significantly reduced by WSMV infection. Root weights from seven genotypes were reduced more than shoot weights. Based on symptoms and ELISA values, five out of eight genotypes, Arapahoe, Vista, Pronghorn, NE89526, and Rawhide, were evaluated as susceptible, two genotypes, Redland and KS93WGRC 27, as tolerant and one genotype, Arlin, as hypersensitive in the present study. Distribution of WSMV titer within the plant was similar for all four tested genotypes, i.e. virus titer in leaves was always higher than that in sheaths and higher in sheaths than roots. However, WSMV titer varied with genotypes, sampling dates, different parts and leaf positions within plant. At two weeks after inoculation, the highest WSMV titer occurred in the lowest leaf for Arlin and Vista, in the second lowest leaf for Arapahoe and in the second highest leaf for KS93WGRC 27. At four weeks after inoculation, the highest WSMV titer usually occurred in the second lowest leaf for all four genotypes. At both two and four weeks after inoculation, the lowest WSMV titer occurred in roots for whole plant and in the youngest leaf among leaves. Virus titer increased slower in tolerant genotypes than in susceptible genotypes. In conclusion, WSMV infection significantly reduced the early growth of winter wheat shoots and roots. Similar to symptoms, WSMV concentration as measured by ELISA in winter wheat plants varies with inoculation period, different parts within plant, leaf positions, and tolerance levels. On the other hand, responses of various genotypes to WSMV infection were also variable. Therefore, use of ELISA in combination with symptomatology will provide the best way to evaluate the tolerance of winter wheat genotypes. However, accurate assessment of tolerance requires samples from the same leaf positions or pooling data from adequate sampling of different leaves and from several sampling dates.

Library of Congress Subject Headings

Wheat streak mosaic virus
Winter wheat -- Diseases and pests
Winter wheat -- Growth

Format

application/pdf

Publisher

South Dakota State University

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