Date of Award

1-1964

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

William M. Epps

Second Advisor

Hugh Macaulay

Abstract

There is very little published information concering the host-parasite relationship between okra (hibiscus esculentus L.) and root-know nematodes (Meloidogyne spp.). This study was undertaken to obtain basic information concerning these relationships that may be helpful in selction of root-know resistant plants and in broadening then knowledge of host-parasite relationships. Okra seedlings of the Clemson Spineless variety wre inoculated with freshly-hatched larvae either in 175 x 34 millimeter test tubes or in nematode observation boxes, both containing moistened expanded vermiculites. Following inoculation of test tuve cultures, seedlings were transplated to sand culture in clay pots and a standard nutrient solution added 3 times weekly. Seedlings were removed at definited time intervals after inoculation to study larval penetration and maturation and host responses to infection. Standard historical and histochemical techniques wre used to study the response of the host to infection. The minimum time required for larval penetration into roots was between 6 and 9 hours following inoculation and penetration continued for at least 24 hours. A higher percentage of inculated larvae was presented within roots after 48 hours than after 24 hours when the lowest larval concentrations (500 and 1000 per plant) were used, but no difference was detected at the highest concentration (2000 per plant). Penetration into the root tip from the root cap to the region of cell elongation accounted for 95.3 percent of the total number of larvae within roots. Approximately 10 to 13 percent of the inoculated larve penetrated and 5.3 to 6.6 percent were ultimately recovered as flask-shaped females. Larvae developed into mature males and females within 19 days following inoculation and the life cycle was completed within 26 days after inoculation. The host responded more readily to infection in the root-tip region than in the mature region 2 to 3 centimeters from the root tip. No galls were visible until 16 days after inoculation in the mature region, while visable enlargement of the root tip occurred within 24 hours after inoculation. Characteristic pathological tissue developed in the mature region even though only very small galls appreared. Giant cells were initiated in the root tips from elongating cells adjacent to the anterior portion of the larvae. Multinucleate cells were first observed 3 days after inoculation and developed by dissolution of cell walls and mitosis without cell division. Giant cell development continued by mitosis, by coalesceing of multinucleate cells and by engulfing of adjacent parechyma until a mazimum size of 250 to 400 x 100 to 250 microns was attained within 21 days following inoculation. Cell walls increased in thickness beginning about 9 days after inoculation and the cytoplasm in the giant cells became more dense as the cells developed. Abnormal parenchyma, which orginated from stimulation of cell division in the pericycle and abnormal xylem elements which developed from xylem parenchyma cells, accompanied all infections. Historchemical studies indicated total protein and ribonucleic acid accumulated in gaint cells and in the bodies of nematodes, and by 26 days after inoculation was far greater than that occuring in adjacent tissues. Walls of the gaint cells appeared to be composed of pectic substances, hemicellulose, and cellulose, with hemicellulose being responsible for the majority of the straining intensity. Starch was not found in giant cells or in accompanying abnomral tissues.

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