Comparison of Soil Receptivity to Thielaviopsis basicola, Aphanomyces euteiches, and Fusarium solani f. sp. pisi Causing Root Rot in Pea

Abstract

Soil receptivity as a quantifiable characteristic ranging from conduciveness to suppressiveness to soilborne pea pathogens Thielaviopsis basicola and Aphanomyces euteiches was determined by analysis of differences in disease response curves obtained by artificial introduction of inoculum into natural field soil samples. Several parameters, including maximum root rot severity, the area under the health index curve, scores on the first axis of a principal component analysis (PCA) on dose responses, and Weibull model fitting were used to describe the disease responses. In all cases, the Weibull model gave satisfactory fits. PCA yielded a first axis that comprised 86% of the variance found when using Weibull predicted responses for T. basicola and 74% of the variance found for A. euteiches. This PCA axis essentially represented the average increase in disease severity due to the addition of increasing doses of inoculum to the soil. The Weibull scale parameter B, which represents the amount of inoculum necessary to increase root rot severity by 63% with respect to the level caused by pathogens naturally present in the soil, is another means of quantifying the receptivity of soils to these plant pathogens. Weibull parameter B, maximum root rot severity, the areaunder the health index curve, and the scores on the first PCA axis were strongly correlated for each of the pathogens tested individually. To compare the extent and behavior of soil receptivity responses to different pathogens, Weibull parameters B and C (slope at dose B) were chosen because of their universal definition, in contrast to PCA scores. Comparison of the average levels of Weibull parameters B and C indicated significant differences between the pathogens. Yet, no significant similarity in the ranking of the soils was found for the three pathogens, demonstrating that individual soils may interact with different pathogens in totally different ways. In general, soils were suppressive to T. basicola but conducive to A. euteiches, whereas their response to Fusarium solani f. sp. pisi ranged from conducive to suppressive. Therefore, risk assessment of soils prior to planting may require different strategies for each pathogen. Bioassays with soil samples taken before the last pea crop in 1987 and 1991 revealed a significant increase in the natural inoculum potential of soils that mainly was accounted for by A. euteiches and Pythium spp. These results strongly indicate that A. euteiches must be considered one of the most threatening pathogens to pea crops in the Netherlands.

Biological control of Aphanomyces euteiches root-rot of pea with spore-forming bacteria

“…Not surprisingly, the level of pathogenic inoculum, or inoculum density, of A. euteiches in field soil can be directly related to disease levels (Boosalis and Scharen, 1959;Chan and Close, 1987a;Oyarzun et al, 1997). The number of oospores per 100 g of field soil and the disease severity were shown to exist in a highly significant, curvilinear relationship (Chan and Close, 1987a) (Figure 1.6).…”

Principal components derived from soil physicochemical data explained a land degradation gradient, and suggested the applicability of new indexes for estimation of soil productivity in the Sakaerat Environmental Research Station, Thailand

“…A significant PC often explains a gradient such as degree of urbanization (Pouyat et al 1995), mycorrhizal infection rate (Karaginnidis and Nikolaou 1999), occurrence of plant disease (Dominguez et al 1996;Oyarzun et al 1997), soil types relating to landscape (Atkinson 1988) or heavy metal contamination reflected in the microbial profile (Muller et al 2001;Rasmussen and Sorensern 2001). Though some soil variables may not show a particular environmental gradient, as with C/N in this research (Tables 1,3), a gradient may be better explained by a PC axis as an integrated measure (Sena et al 2000) As in the current research, Broughton and Gross (2000) reported that the first PC explained soil productivity, and was significantly related to soil microbial functions.…”

Molecular assays reveal the presence and diversity of genes encoding pea footrot pathogenicity determinants inNectria haematococcaand in agricultural soils

“…Moreover, peas were also grown on culture medium inoculated with 0·5% Tween without fungal conidia as a control. Root disease was assessed after 7 days using a disease index (DI) scale of 0–5 (0 = no root discolouration; 1 ≤ 20%; 2 = 21–40%; 3 = 41–60%; 4 = 61–80%; 5 ≥ 81% discolouration) (VanEtten and Kistler 1988; Oyarzun et al. 1997).…”