Document Type

Thesis - University Access Only

Award Date

2002

Degree Name

Doctor of Philosophy (PhD)

Department / School

Agronomy

Abstract

Fusarium head blight (FHB) or scab, caused by Fusarium graminearum Schwabe, and tan spot, caused by Pyrenophora tritici-repentis (Died.) Drechs., have emerged as economically important diseases of spring wheat (Triticum aestivum L.). Losses to these diseases have increased in recent years, particularly under reduced-tillage systems. Breeding for resistance is the only practical and sustainable method of control in the long run. Susceptibility to FHB could be related to the resistance to tan spot and vice versa; however, information on such interaction is lacking. Based on the preliminary studies, five spring wheat lines were chosen for this study. CIMMYT 7 and 2375 were intermediate in resistance to FHB, while CIMMYT 7 and Seri 82 were resistant/moderately resistant to tan spot. Fang 60 and Sonalika were susceptible to both FHB and tan spot. Ten spring wheat populations, derived from these five parents in all possible combinations, were evaluated for reaction to FHB and tan spot both in the field and greenhouse. Data were recorded and analyzed on four variables, FHB index (FHBI) and Fusarium damaged kernels (FDK) for FHB, and adult plant (TSaduit) and seedling (TSscedling) for tan spot. General combining ability (GCA) and specific combining ability (SCA) were estimated for all variables using Griffing's diallel method-4, model- I. Correlation coefficients were calculated to measure the interaction. Both GCA and SCA were highly significant; GCA was consistently larger than SCA for all the variables in all the experiments conducted in the field and greenhouse. CIMMYT 7 and 2375 had the largest GCA for resistance (negative value) to FHB, while CIMMYT 7 and Seri 82 were the best for tan spot resistance. Fang 60 and Sonalika had the largest GCA for susceptibility (positive value) to both FHB and tan spot. With few exceptions, ranking of GCA effects and corresponding per se disease ratings of the five parents, for respective variables, were similar. Transgressive segregants of both resistant and susceptible types were observed in almost all the populations for both FHB and tan spot. With few exceptions, there was no correlation between FHB and tan spot resistance. Resistance to adult plant tan spot appeared to be correlated with late maturity, but resistance to seedling tan spot, with few exceptions, was not correlated with maturity. Association of FHB (FHBI and FDK) to maturity appeared to be genotype or population dependent. A positive and significant correlation was found between FHBI and FDK. FHBI and FDK ratings from the field were correlated respectively with FHBI and FDK ratings from the greenhouse. Resistance to adult plant (field) tan spot was correlated with the resistance to seedling (greenhouse) tan spot, but with a few exceptions.

Format

application/pdf

Number of Pages

117

Publisher

South Dakota State University

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