2.8.5S
NEMATODES AND PLANT PHYSIOLOGY: NUTRITION, ALLOMETRY AND YIELD

EP CASWELL-CHEN

Department of Nematology, One Shields Avenue, University of California, Davis, CA 95616, USA

Background and objectives
Uptake, processing, and allocation of nutrients are of primary importance in determining plant fitness. The nematode-plant interaction is a feedback loop, in which nematodes influence plant nutrition and growth, while plant support for the parasite returns as feedback to influence nematode development and reproduction. This feedback may be considered at various levels of resolution, from signalling to nematode management and crop loss assessment. Depending on their density, phytoparasitic nematodes interfere with root phenology and homeostasis, and hence disrupt nutrient uptake, processing, allocation and yield.

Results and conclusions
Nematodes act as nutrient sinks within plant roots, influencing plant nutrient uptake. In short-term solution-culture experiments with coffee, the sedentary endoparasite Meloidogyne konaensis reduced NO3- uptake rate by 63% and NH44+ uptake rate by 54%, while the migratory endoparasite Pratylenchus coffeae reduced the uptake rates of NO3- and NH44+ by 56% and 24%, respectively [1]. The nematode-induced modification of nutrient uptake alters the rate of plant biomass accumulation, allometry, and yields. Thus, the feedback loop between host and parasite is evident at larger scales, and has ramifications for nematode management within and across seasons.

Nematologists attempt to define quantitative damage relationships that describe the dependence between nematode density, plant growth, and yield. The damage observed within a season is a function of realized plant resource allocation relative to parasite density, while the damage potential across seasons is dependent on nematode reproduction, itself a function of host suitability. The data used to derive damage functions must include accurate measurements of nematode densities. Accuracy is decreased by several factors, including the aggregated spatial pattern of nematodes within fields, and undetected nematode development and reproduction on root fragments [2].

References
1. Vaast PH, Caswell-Chen EP, Zasoski RJ, 1998. Biology and Fertility of Soils 26, 130-135.
2. Gardner J, Caswell-Chen EP, 1997. Fundamental and Applied Nematology 20, 269-276.