The Relation Between Nematode Density and Damage To Plants

Abstract

An equation for the relation between the density of stem nematodes or virus transmitting nematodes in the soil and the proportion of attacked plants can be derived if two suppositions are made: 1. the "average nematode" is the same at all densities. 2. the nematodes act independently of each other. If now y = the proportion of the plants that is not attacked and P = the density of the nematode then In this equation z is a constant < 1 and equal to the proportion of the plants not attacked at a nematode density P = 1 (competition curve of Nicholson). The results of a pot experiment by Sayre & Mountain and field observations by Kaai are in close agreement with this equation. To describe the relation between the density of populations of root infesting nematodes and the yield of attacked plants an equation must express two phenomena: 1) Up to a certain density (the tolerance limit) the yield is not affected (damage only to tissue that is not essential to the growth of the plant, power of recovery of the plant), 2) a certain minimum yield (Omin) remains unaffected by the nematodes even at the highest densities (because of temporary or continuous inaccessability of part of the host tissue). The equation in which Op = yield at nematode density P, 0max = yield in the absence of nematodes and T = tolerance limit, fulfills these requirements. The results of many experiments reported in the literature are in good agreement with this theoretical relation between nematode density and yield. In most cases Omin is between 0.1 Omax and 0.5 Omax. The tolerance limit depends on the nematode species, the plant species and external conditions.

Construction and preliminary evaluation of a simulation model of the population dynamics of the potato cystnematode Globodera pallida

“…3. The form of relation derived by Seinhorst (1965) and shown experimentally by Den closely resembles that predicted by the model. The density above Neth.…”

“…Oostenbrink, 1966;Jones, 1966;Jones et al, 1967;Seinhorst, 1967Seinhorst, , 1968Raeuber and Stelter, 1970;Jones and Kempton, 1978;Jones and Perry, 1978;Mugniery, 1976). Others determine, empirically, the relation between yield and the initial egg density (Seinhorst, 1965(Seinhorst, , 1983. Two studies, however, describe the timing of certain changes in population structure as a function of accumulated temperature (Mugniery, 1978b;Jones and Perry, 1978).…”

Population dynamics of Meloidogyne incognita on cucumber grafted onto the Cucurbita hybrid RS841 or ungrafted and yield losses under protected cultivation

“…It allows comparing nematode population dynamics on different plant species or germplasms or between cropping seasons for a given pathosystem and the efficacy of control methods (Talavera et al 2009 ;Vela et al 2014 ). Those parameters refer to nematode population growth but do not provide valuable information on marketable crop yield, which is provided by the relationship between Pi and relative crop yield by the Seinhorst damage function model, the tolerance limit and the minimum relative yield (Seinhorst 1965 ). It is known that plant growth and yield are reduced at increasing Pi above the tolerance limit due to a reduction of water and nutrient intakes, and consequently, a reduction of plant conductivity and transpiration, as well as leaf chlorophyll content and photosynthesis rate (Loveys and Bird 1973 ;Melakeberhan 2003 to Pi (Melakeberhan et al 1985 ;Giné et al 2014 ;López-Gómez et al 2015 ).…”

Natural occurrence of fungal egg parasites of root-knot nematodes, Meloidogyne spp. in organic and integrated vegetable production systems in Spain

“…In Germany, plant parasitic nematodes are widely spread in organic vegetable production and can cause severe damage (Hallmann et al 2007). Despite yield losses due to plant parasitic nematodes are related to the population densities at planting and the plant tolerance (Seinhorst 1965), the cropping system could also influence the population dynamics of the nematodes, due to changes in the antagonistic potential of soils, and can thus affect the relationship between yield losses and nematode population densities. Long-term studies should be done to determine the effect of native fungal egg parasites on the population dynamics of RKN and crop yield of the most common rotation sequences, and to improve agronomical practices that enhance the level of suppression of plant parasitic nematodes.…”