Browsing by Author "Joyner, Bobby Gerald"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Influence of Trichoderma Harzianum Rifai on growth, chemical compositions and root exudation of axenic tobacco
    Joyner, Bobby Gerald (Virginia Polytechnic Institute and State University, 1975)
    Tobacco plants (Nicotiana tabacum L. 'Virginia Gold') grown axenically in gnotobiotic flexible vinyl isolators, were inoculated after 44 days growth with washed conidia of Trichoderma harzianum Rifai by introducing conidia into the rooting medium at a concentration of 1.08 X 106 to 1.44 X 106 conidia per plant. Experiments were harvested 35 days and 123 days after inoculation. Growth measurements were made, shoot and root tissue dried for 48 hours at 75 C and ground. Chemical analyses were made on the dried tissue. Root exudates were collected at the end of experiments and weekly for 12 weeks. Exudate collection was made by leaching the rooting medium with one-half strength nutrient solution while plants were in place, Chemical analyses were conducted on concentrated root exudates. Inoculated plants were similar in size, but contained more senescent leaves than did axenic plants. Axenic plants flowered sooner and in greater numbers than did inoculated plants. Similar amounts of total water soluble carbohydrates, reducing sugars, fructose, starch, nicotine, nitrogen, and protein were found in axenic and root-colonized plants. Sodium content was consistently greater in the inoculated plants. Manganese and barium were in larger quantities in plants colonized for 35 days but not after 123 days of colonization. The contents of copper and potassium were greater in leaves from plants colonized for 123 days, however, these same plants contained less zinc, aluminum and molybdenum than axenic plants. The root mass was more elongated on colonized plants, but dry weight of the same tissue was lower than axenic roots. Examination of inoculated roots gave no evidence of tissue degradation. Histological examination of the tissue, however, revealed extensive colonization by T. harzianum. Conidial germination occurred after 6 days, primarily in the root hair zone. The fungus penetrated root hairs and colonized the root tissue external to the stele. Exudates of colonized roots had a lower content of total water soluble carbohydrates and reducing sugars. The reduction became more significant with increasing fungal colonization. The reduction was attributed to the compounds being utilized by T. harzianum. Exudates of colonized roots contained a higher carbohydrate to reducing sugar ratio than exudates of axenic roots. The initiation of flowering by axenic plants may have caused a reduction in the total water soluble carbohydrates, reducing sugars and amino acids in root exudates.