Date of Award:

5-1981

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Committee Chair(s)

Neal Van Alfen

Committee

Neal Van Alfen

Abstract

Symptoms of dark crown necrosis were found in all fields and varieties of alfalfa examined throughout the state. No significant differences were noted among varieties in 1 year old test plots in the amount of disease (Disease Index = D.I.) present in crown tissue. Significant differences were noted in plots 2.4 years and older among the different varieties. Varieties common to all plots did not differ overall; however, varieties responded differently according to location.

Fusarium spp. were most frequently isolated from affected crowns throughout the state, yet, differences in occurrence of species among the different aged plots and fields were noted. F. solani, F. oxysporum, F. roseum 'Accuminatum', and Phoma sp. were inoculated singly and in combination into 3 to 4 month old alfalfa crowns established in the field. All treatments were significantly different from the uninoculated control. Mean disease index (D.I.) for crowns inoculated with F. solani was highest and significantly different from the H2O inoculated control. Four different fields, aged 2 to 11 years old, were assessed for impact. No significant differences in mean stems per 900 cm2 were found among the fields despite the significantly higher mean D.I. of 11 year old crowns vs. the younger crowns.

Despite significantly lower numbers of crowns in the 11 year old field, older crowns produced 4 times as many stems as 2 year old crowns. How stem numbers per 900 cm2 relates to actual yield and quality among the different aged fields was not determined.

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