Geostatistical Analysis of Field Spatial Distribution Patterns of Soybean Cyst Nematode

Abstract

Site‐specific management of soybean cyst nematode [Heterodera glycines Ichinohe] (SCN) is plausible if its spatial and temporal dynamics are adequately known and structured. The hypothesis that variation in the spatial distribution of SCN is sufficient in magnitude and structure and sufficiently time invariant to support the use of site‐specific management in SCN‐infested fields was tested. A nested survey sampling design with distances reduced by geometric progression was applied on two fields in Michigan. Cysts were extracted from single‐core soil samples collected before planting in 1999 and 2000, the number of eggs per cyst was estimated, and the number of eggs per sample was obtained by multiplying eggs per cyst by the number of cysts. The distribution of the three variables was characterized using geostatistical tools such as semivariograms, kriging, and cross‐correlograms on log‐transformed values of the original data. Mean cyst population density ranged from 6 to 33 cysts 100 cm−3 soil in the two fields. Although the spatial structure of SCN population varied between fields and SCN population density varied between years, the location of areas of high or low cyst density could be identified repeatedly. The reasons why nematodes exhibited an aggregated distribution are not yet understood. The evaluation of factors associated with the determination of SCN spatial distribution is part of an ongoing project toward the development of SCN site‐specific management.

Leaf constituents of Curcuma spp. suppress Meloidogyne hapla and increase bacterial-feeding nematodes

“…Among other things, this leads to invasion by opportunistic and nutrient cycling organisms that feed on decaying materials. The presence of Rhabditis (c-p 1) and Acrobeloides, Cephalobus and Eucephalobus (c-p 2), all early colonisers and fast reproducing nematodes, supports the notion of invasion by opportunistic organisms that are not harmful to plants (Bongers, 1990;Yeates et al, 1993;Avendaño et al, 2003;Okada & Kadota, 2003).…”

Spatio-temporal consideration of soil conditions and site-specific management of nematodes

“…There are two points worth noting here: (i) the problem cannot be solved without simultaneous consideration of the soil conditions and SCN, and (ii) the soil conditions would not have been clearly identified without consulting USGS soil maps. It was evident from this data set that a simple Samples were collected in a soybean field in Shiawassee County, Michigan, following a geostatistical sampling design described in Avendaño et al (2003). Data are from Avendaño (2003) cause-and-effect relationship could not be established, but that there was a complex relationship involving the effects of soil physical and chemical characteristics on the nematode and the plant, disturbing the host-parasite relationship, thus demonstrating the need to look beyond limited horizons (Wallace 1978).…”

Effect of starter nitrogen on soybeans under Heterodera glycines infestation

“…Nematode life stages in soybean roots were determined by staining 2 g sub-samples in acid-fuchsin (Hussey 1985). Cysts were extracted from a 100 cm 3 using the centrifugation method (Jenkins 1964) in 1998 and using a semi-automatic elutriator (Research Services Instrument Shop, The University of Georgia, Athens, GA) with 60% extraction efficiency in 1999 (Avendaño et al 2003). Eggs per cyst were estimated by randomly crushing 3 cysts per sample and counting eggs and second-stage juveniles, and the average used to determine the eggs per cyst for each sample (Avendaño et al 2003).…”

“…Cysts were extracted from a 100 cm 3 using the centrifugation method (Jenkins 1964) in 1998 and using a semi-automatic elutriator (Research Services Instrument Shop, The University of Georgia, Athens, GA) with 60% extraction efficiency in 1999 (Avendaño et al 2003). Eggs per cyst were estimated by randomly crushing 3 cysts per sample and counting eggs and second-stage juveniles, and the average used to determine the eggs per cyst for each sample (Avendaño et al 2003). The total population density per 100 cm 3 of soil was calculated as the total numbers of cysts multiplied by the numbers of eggs per cysts (Avendaño et al 2003).…”

“…Eggs per cyst were estimated by randomly crushing 3 cysts per sample and counting eggs and second-stage juveniles, and the average used to determine the eggs per cyst for each sample (Avendaño et al 2003). The total population density per 100 cm 3 of soil was calculated as the total numbers of cysts multiplied by the numbers of eggs per cysts (Avendaño et al 2003).…”