Graduate Thesis Or Dissertation
 

Studies on the vesicular-arbuscular mycorrhizae of Easter lily in the Pacific Northwest

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  • A study was conducted to characterize the vesicular-arbuscular (VA) mycorrhizal fungi of commercially grown Easter lily. Monthly field soil and root samples were collected from March through September, 1975, from five fields in the coastal area of southern Oregon and northern California. Soil sievings were inoculated onto clover, onion and lily to increase mycorrhizal spore numbers and to facilitate identification. Four different VA mycorrhizal species were found: Acaulospora elegans, A. trappei, Glomus fasciculatus, and G. monosporus. All four VA species infected Easter lily, clover, and onion. A. trappei and G. fasciculatus were the most frequently isolated species from all five fields. Two of the five fields under study contained only two mycorrhizal species, and three fields contained all four species. Mycorrhizal infections in roots of field grown lilies were young and sparse in March and gradually increased until September when bulbs were harvested. Root systems became over 75% infected with mycorrhizae in fields with four species, while in fields with two mycorrhizal species, usually 50% or less of the root stystems became mycorrhizal. High infection levels were reached more rapidly in fields with four VA species present. Lilies were inoculated in the greenhouse with roots and spores from onion, lily, and clover trap plants. Two levels of mycorrhizal inoculum and three fertilizer rates were tested for their effects on lily growth. Controls were either non-inoculated or inoculated with a solution from the mycorrhizal inoculum which had passed through a 38 μm sieve to remove mycorrhizal spores. Plants given either the high or low level of inoculum did not grow as well as controls. These results were apparently attributable to root rot caused by Fusarium oxysporum which had increased along with the mycorrhizae on trap plants, and was subsequently inoculated onto lilies. More F. oxysporum was recovered from roots inoculated with mycorrhizae than from control plants inoculated with a sieving solution. None was recovered from the non-inoculated plants. The high fertilizer level reduced mycorrhizal infection and enhanced root disease incidence. However, there was more mycorrhizal infection in roots given high fertilizer than no fertilizer. The most mycorrhizae formed in plants given the low fertilizer rate. A Rhizoctonia-like fungus was found to infect field grown lilies. No apparent adverse or beneficial effects on lily by this fungus were observed under any of the same three fertilizer levels used in the mycorrhizal inoculations. Another experiment was conducted in order to test the effects of a single mycorrhizal species on Easter lily growth in the absence of pathogens. Lily seedlings were inoculated with A. trappei in the form of spores and infected root fragments from an A. trappei-red clover pot culture. Controls were given a sieving solution made from the mycorrhizal inoculum. Plants inoculated with A. trappei grew significantly better than the controls (fresh weight). Mycorrhizal plants also had a higher level of N, P, K, Ca, and Mg than nonmycorrhizal controls. If the benefits shown in this greenhouse study also occur on field grown plants, then mycorrhizae may have practical application in Easter lily bulb production.
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