Date of Award

1988

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Plant Pathology and Crop Physiology

First Advisor

Jeffrey W. Hoy

Abstract

The nature of resistance to smut, caused by Ustilago scitaminea Syd., was evaluated in 15 sugarcane, interspecific Saccharum hybrid, clones with smut reactions ranging from resistant to highly susceptible. No association was found between smut infection level and bud traits including length, width, length x width, shape, flange, groove, germination type, germination times, and shoot growth rates. In two clones, inoculation of plants with initial shoot lengths up to 6 cm resulted in high smut infection levels, whereas inoculation of ungerminated buds or plants with longer shoots resulted in low infection levels. Resistance to systematic infection was detected in plants of resistant and susceptible clones following wound inoculation. Heritability of resistance was determined by comparing smut infection percentages of parents and offspring in plant cane and first ratoon from 18 biparental crosses involving resistant, moderately susceptible, and highly susceptible clones. Resistant progeny frequencies were highest in resistant x resistant crosses. Resistance was moderately heritable; narrow-sense heritability estimates of 0.41 $\pm$ 0.08 and 0.38 $\pm$ 0.11 were obtained in plant cane and first ratoon, respectively. Heritability estimates from (mid-) parent-offspring regression and standard units methods were not biased and were more precise than those from factorial analysis of variance. Additive variance was the major genetic component of smut resistance. Clone smut reactions were moderately repeatable for plant cane in two subsequent years and from plant cane to first ratoon. Significant changes in smut infection percentages occurred between plant cane and first ratoon in moderately and highly susceptible clones. Genetic gain in resistance estimates increased from 5 to 24% as selection intensity decreased from 70 to 5%. Results indicate that resistant progeny frequencies in the Louisiana sugarcane breeding program can be increased by careful parent selection.

Pages

112

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