Masters Theses

Date of Award

6-1987

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Ernest C. Bernard

Committee Members

Leander F. Johnson, Paris L. Lambdin, Carol J. Southards

Abstract

In greenhouse experiments, Heterodera glycines Ichinohe juveniles invaded clover and alfalfa roots to the same degree as 'Essex' soybean, but fescue, rye, barley and wheat were not significantly invaded and thus did not act as trap crops. When wheat and barley were grown simultaneously with soybean, each significantly reduced invasion of H. glycines juveniles into soybean. Sunflower grown simultaneously with soybean significantly reduced the number of females maturing in soybean. An experiment was conducted to further study the effect of wheat rhizosphere on invasion and maturation of nematodes in soybean. There were three basic treatments: steam-sterilized soil was infested with nematode eggs, then planted with soybean seedlings; steam-sterilized soil was infested with eggs, then greenhouse fallowed (watered at the same times as other treatments) for 15, 30 and 60 days, then planted with soybean seedlings; and steam-sterilized soil was infested with eggs, and planted with wheat allowed to grow for 15, 30 and 60 days before crowns were excised after which soybean seedlings were planted. Soybean roots were harvested at ages 20, 40 and 60 days. In soil with 30 days of pretreatment, soybeans grown for 40 days after killed wheat had greater numbers of female nematodes than soybeans 40 days old harvested from fresh or fallowed soil. In soil with 60 days of pretreatment, soybeans 40 days old grown after killed wheat had simultaneously fewer juveniles and greater numbers of females than soybeans 40 days old harvested from fresh or fallowed soil. Regardless of length of pretreatment, soybeans 20 or 60 days old in wheat treatments were not significantly different from soybeans in both controls at the same time. These results could be interpreted as evidence that greater initial numbers of H. glycines eggs hatch in response to soybean planted after killed wheat and that a lower rate of hatch over a longer period of time occurs in eggs from fallowed or fresh soil immediately planted with soybean. In an experiment with nematode eggs placed in soil, nematodes hatched, migrated through root systems of wheat or sunflower or through nylon monofilament in soil, and invaded roots of soybean plants. Significantly fewer female nematodes were found 40 days after infestation of soil in soybean roots surrounded by filament or other plants than in soybean roots surrounded only by soil. The physical presence of nonhost roots, poor-host roots and root-like filaments may interfere with nematode host searching abilities.

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