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United States Department of Agriculture

Agricultural Research Service

Research Project: GENOMICS, GERMPLASM DEVELOPMENT AND IPM OF HOP

Location: Forage Seed and Cereal Research

Title: Spatial characteristics of white mould epidemics and the development of sequential sampling plans in Australian bean fields

Authors
item Jones, Suzanne -
item Gent, David
item Pethybridge, Sarah -
item Hay, Frank -

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 17, 2011
Publication Date: May 12, 2011
Citation: Jones, S.J., Gent, D.H., Pethybridge, S.J., Hay, F.S. 2011. Spatial characteristics of white mould epidemics and the development of sequential sampling plans in Australian bean fields. Plant Pathology. DOI:10.1111/j.1365-3059.2011-02466.x.

Interpretive Summary: White mould is a damaging disease of bean that can result in complete loss of marketable crops. In this study, we assessed the patterns of the disease on pods and developed statistical methods to efficiently estimate disease incidence to improve disease sampling and monitoring. The spatial patterns of the disease indicated that epidemics may be dominated by localized sources of inoculum, most likely within the field of interest. Using a procedure called sequential classification, correct decisions on disease status were made in at least 95% of fields used to validate the sampling protocol after assessment of only 10 to 15 plants. The outcomes of this research provide the basis for implementing more efficient sampling and management strategies for white mould of bean.

Technical Abstract: White mould, caused by Sclerotinia sclerotiorum, causes losses to bean through reducing the marketable yield of pods by flower infections and stem rot. In Australia, entire fields may be rejected due to high disease incidence. The spatial characteristics of white mould epidemics were characterised in 54 linear transects (data sets) collected from a total of 18 bean fields during 2008 to 2010 in northern Tasmania, Australia. In all fields, the incidence of diseased pods and plants was assessed using a cluster sampling design prior to harvest. Distributional and correlation-based analyses indicated that the incidence of diseased pods was characterised by a largely random pattern at the scale of individual plants, with some patches of plants with similar disease levels on pods occurring at a scale of 1.5 metre or greater. Collectively, these results suggested that epidemics may be dominated by localized sources of inoculum, most likely within the field of interest. Sequential sampling approaches were developed to estimate disease incidence or classify disease incidence above or below provisional thresholds of 3, 5%, and 15% incidence on pods near harvest. Achieving pre-specified levels of precision by sequential estimation was possible only when disease incidence on pods was greater than approximately 4% and sampling was relatively intense (i.e., 10 pods evaluated on each of at least 64 sampling units). Using sequential classification, correct decisions on disease status were made in at least 95% of independent validation data sets after assessment of 10.06 to 15.03 plants, depending on the classification threshold and error rates specified. The outcomes of this research provide the basis for implementing more efficient sampling and management strategies for white mould of bean in Australian fields.

Last Modified: 10/1/2014