Date of Award

1999

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Plant Pathology and Crop Physiology

First Advisor

Edward C. McGawley

Abstract

A survey conducted from May 1995 through August 1998 revealed diverse nematode communities in sugarcane fields in Louisiana. High populations of Mesocriconema, Paratrichodorus, Pratylenchus, and Tylenchorhynchus were widespread in nine sugarcane production parishes. Comparisons of plant cane and ratoon sugarcane crops indicated that nematode community levels increase significantly in successive ratoon crops. Greenhouse experiments evaluated the susceptibility of sugarcane cultivars to a nematode community comprised of Mesocriconema xenolax, Paratrichodorus minor, and Tylenchorhynchus annulatus. Across years (1995 and 1996) and cultivars (CP 65--357, CP 70--321, LCP 82--89, HoCP 85--845, and LCP 86--454), plant height, shoot length, top and root dry weight, and the number of tillers per plant were reduced by nematodes. Growth parameters of the LCP cultivars were most affected by the nematodes, and those of cultivars HoCP 85--845 and CP 65--357 were least affected. The susceptibility of cultivars to nematodes also was evaluated in microplot experiments. Across years (1995, 1996, and 1997) and cultivars (CP 70--321 and LCP 82--89), nematodes reduced top and root dry weight and number of tillers per plant. LCP 82--89 supported higher nematode community levels and sustained the greatest amount of root damage. Nematicide trials evaluated the efficacy of aldicarb, ethoprop, and phorate against indigenous nematode populations. Aldicarb consistently increased the number of millable stalks, cane tonnage, and the yield of sucrose in soils with a high sand content. Yield increases were concomitant with reductions in the density of the nematode community shortly after planting and at harvest. In soils with a higher clay content, the chemicals were less effective in controlling nematode populations, and as a result, yield increases were minimal. Greenhouse experiments conducted in 1996, 1997, and 1998 evaluated the single and combined effects of nematodes and the sugarcane root-rot pathogen, Pythium arrhenomanes. Individually, P. arrhenomanes and nematodes reduced top and root dry weight. Temperature had a significant influence on nematode reproduction and Pythium colonization. Interactions between P. arrhenomanes and nematodes were antagonistic with regard to root dry weight and nematode reproduction.

ISBN

9780599474314

Pages

70

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