Graduate Thesis Or Dissertation
 

Population dynamics, extraction, and response to nematicide of three plant parasitic nematodes on peppermint (mentha piperita L.)

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  • The efficiencies of wet sieving/sucrose centrifugation (WS/SC) recovery of Pratylenchus penetrans (59 %), Paratylenchus sp., (80 %), and Criconemella xenoplax (66 %) were established. Baermann funnels (BF) recovered significantly more P. penetrans (p = 0.01) and significantly less (p = 0.01) C. xenoplax than did WS/SC. While densities of P. penetrans in stored soil remained constant over the three days following field sample collection, Paratylenchus sp. and C. xenoplax densities increased significantly on the second day and decreased to their original level on the third day. During mist chamber extraction, P. penetrans continued to emerge from peppermint root tissue for 38 days, but 90 % of the total was recovered after 10 days. The standard core, consisting of 500 g dry soil plus the roots and rhizomes in that soil, was developed to express endoparasitic and ectoparasitic nematode densities in peppermint field soil, roots, and rhizomes. Enumerating nematode densities within the different plantsoil components of a particular volume of soil more closely describes the total nematode population pressure on the plant growing in that volume of soil. Therefore, endoparasitic nematode population levels were expressed as numbers in standard core soil, roots, rhizomes, or total core (soil, root, and rhizome populations combined). P. penetrans populations in peppermint fields peaked in early May, decreased through the summer, peaked again in August, and decreased through the fall to a low winter level. Peaks in the P. penetrans population followed peppermint root weight peaks by 3 to 6 wks. Paratylenchus sp. populations remained at relatively low levels throughout the year except for a pronounced peak in August, which followed the root weight peak by 3 to 6 wks. The C. xenoplax population also peaked 3 to 6 wks after the August root weight peak but fluctuated markedly throughout the remainder of the year. From 70 to 90 % of the total P. penetrans population was in roots in early May, decreased to 40 to 50 % by late June and 20 to 40 % in August. Up to 20 % of the population was in rhizomes on some dates, but the rhizome percentage was usually less than 10. Fewer P. penetrans were recovered from rhizomes during the harsh winter of 1988-89 than during the mild winter of 1989-90. Analysis of point samples (pretreatment, posttreatment, and harvest samples) and area under nematode population curves (AUNPC) were used to compare nematode populations in oxamyl-treated (1.1 kg a.i./ha) and nontreated plots in two peppermint fields through the two growing seasons. Point sample analyses detected significant decreases in treated soil, root, and total standard core P. benetrans populations compared to nontreated populations in several pretreatment and harvest sample dates and in two rhizome harvest sample dates. No treatment differences were observed in Paratylenchus sp. or C. xenoplax populations using this analysis. AUNPC analysis detected significant decreases in several treated root and rhizome P. penetrans populations compared to nontreated populations and in total core populations in field 1 during one growing season and in field 2 during two growing seasons. Significant decreases in C. xenoplax populations were observed in one field during one growing season. Peppermint hay weight was significantly greater in treated than in nontreated plots in one of three fields in 1988 and in one of three fields during 1989. Oil in ml/kg fresh hay weight was significantly lower in treated than in nontreated plots in one of three fields during 1989. No treatment differences were detected in milliliters of oil distilled from 2m² field area. Peppermint oil production is the final measure of a treatment from a mint grower's perspective. Because oxamyl had no effect on mint oil production, AUNPC appears to be a better measure of parasitic nematode pressure on peppermint, since this method of analysis detected fewer significant differences between nematode populations between treated and non-treated plots.
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