Document Type

Dissertation - Open Access

Award Date

1960

Degree Name

Master of Science (MS)

Department / School

Plant Science

Abstract

Corresponding to the title, the present study was concerned with two aspects. In the first of these, two chlamydosporous sori from corn were collected from California and Washington and 18 chlamydosporous sori from sorghum were collected from California, New Mexico, Texas, and India. Chlamydosporous cultures or paired monosporidial cultures from these were hypodermically injected as desired into seedlings of one or more of four sweet corn varieties and 57 sorghum varieties. Chlamydosporous cultures from the two corn sources yielded head smut on three sweet corn varieties and not on any of 14 sorghum varieties. Cultures from 14 of 18 sorghum sources yielded head smut on Sugar Drip sorghum and on North Star sweet corn, while cultures from the remaining four yielded head smut only on Sugar Drip sorghum. The 18 sorghum head smut cultures were differentiated on a set of five sorghum varieties, and comprised four races according to sources; (1) California, (2) Poona 1 and Coimbatore 2, (3) Poona 2 and (4) Texas, New Mexico and Coimbatore 1. The difference between the sorghum and the corn head smut fungi accordingly was considered to be varietal, rather than racial as supposed by Reed. The sorghum and the corn head smut fungi were readily hybridized. In the second part of the study, chlamydospores germinated in soil by forming long multicellular hyphae, the lower cells of which were empty while the apical cells filled with vacuolated or nonvacuolated protoplasm. The absence of sporodial formation may account for the low number of races found in this pathogen and for the apparent natural stability of the sorghum and corn head smut fungi as separate units. Chlamydospore abundance in soil affected the per cent incidence of head-smutted sorghum plants. Within limits the per cent incidence of head-smutted sorghum plants was linearly related to the logarithm of the number of chlamydospores in soil. The threshold number of viable spores necessary for infection being estimated at about 800 per gram of soil. The abundance of infectious chlamydospores in soil declined rapidly after 7 days to sub-threshold levels at a temperature of near-freezing, regardless of soil moisture. The decline at 10°, 20° and 30°C, and at soil moistures near the wilting point, 20%, 40% and 100% of field capacity was less rapid and in most instances did not reach the threshold limit within 30 days. In supplementary studies sorghum seeds carrying 52,631 or 404,578 chlamydospores per seed failed to yield smutted plants. A dominant form of resistance to head smut was contributed by FC 811 Faterita to a sorghum hybrid. Sorghum head smut is a widely distributed disease of sorghum reported from Africa, Argentina, Brazil, China, India, Italy, Japan, Middle Easer New South Wales, Soviet Union and Unites States. It is the result of infection of seedlings by germinating seed or soil-borne chlamydospores of the fungus Sphacelotheca reiliana (Kuhn) Clint., which fungus completely destroys the inflorescence of the growing plant, replacing it with its own body of mycelium and chlamydospores. Corn is also attacked by the fungus and sustains the disease.

Library of Congress Subject Headings

Sorghun -- Diseases and pests
Spacelotheca reiliana

Description

Includes bibliographical references

Format

application/pdf

Number of Pages

100

Publisher

South Dakota State University

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