Date of Award

1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Plant, Enviromental and Soil Sciences

First Advisor

Stephen A. Harrison

Abstract

Bacterial leaf streak or black chaff caused by Xanthomonas campestris pv. translucens (Xct) can cause yield loss in wheat, especially in warm, high rainfall environments. Bactericidal chemicals have not been effective in controlling the disease, however, host resistance to leaf streak may be an effective control measure. Studies were conducted in the field and greenhouse to determine the relationship between the black chaff and leaf streak symptoms caused by Xct, to quantify yield loss, to calculate the heritability of leaf streak reaction and to evaluate germplasm for resistance to leaf streak. The results showed that 'Florida 304' is very susceptible to leaf streak but is resistant to black chaff. All other cultivars tested are susceptible to both black chaff and leaf streak. In the field, average leaf streak severity on individual flag leaves ranged from 2% on 'Terral 101' to 11% on Florida 304 at Feekes' growth stage 10.5.4. Yield losses estimated from these levels of leaf streak were 3% and 9% in Terral 101 and Florida 304, respectively. There was no relationship between black chaff severity and yield. Estimates of the narrow sense heritability of reaction to leaf streak range from 0.12 to 0.70 and averaged 0.31. Entry mean heritability increased to 0.47 with testing over three replications at one location. Lastly, 64 bread wheat lines were identified that were resistant to leaf streak in two years of field testing. These studies show that some cultivars may be resistant to black chaff but susceptible to leaf streak and that yield loss is related to leaf streak and not black chaff. Yield loss caused by leaf streak was estimated at 9% in Florida 304, the most susceptible cultivar tested. This is not a severe yield reduction, given the susceptibility of Florida 304 to leaf streak. Thus, a high level of resistance to leaf streak in winter wheat may not be needed to avoid yield loss. Screening wheat for resistance to leaf streak in replicated plots under artificial inoculation should be very successful for identifying lines that are resistant to leaf streak.

Pages

109

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