NYMPHSTAR: an accurate high-throughput quantitative method for whitefly (Aleurotrachelus socialis Bondar) resistance phenotyping in cassava

Abstract

Abstract Background Whitefly (Aleurotrachelus socialis Bondar) is an important pest causing high economic losses in cassava production systems in the north of South America. It reduces the plant’s photosynthesis by colonizing the cassava leaves and either directly feeding on their phloem sap or excreting substances that allow the growth of sooty mold and the consequent reduction of the photosynthetic area. The deployment of the crop’s natural resistance to this pest is the most effective approach to its management. Phenotypic evaluation to identify germplasm with superior whitefly-resistance (WFR) levels from that showing a whitefly susceptible (WFS) response will benefit from the availability of an accurate high-throughput, quantitative phenotyping method. Results We developed an accurate and efficient image-based phenotyping method (Nymphstar) to quantify the total number of third and fourth instar nymphs through red, green, and blue color space (RGB) image analysis as a plugin for ImageJ. Nymphstar estimates both the number of third and fourth instar nymphs and the percentage of leaf area they occupy. We tested 19 cassava genotypes and classified them after data analysis as resistant or susceptible to A. socialis attack. Benchmarking Nymphstar against manual nymph counts performed by a specialist revealed a highly significant correlation between direct nymph counts and those estimated using Nymphstar, which analyzed images and counted nymphs 150 times faster than by manual counts. Full-bench caging for a free-choice assay facilitated our assessment of WFR in the cassava germplasm and early replicated trials in the experimental population and enhanced the efficiency of whitefly (A. socialis) colonization on each cassava genotype to accurately depict the intensity of the resistance/susceptible response under a choice regime, simultaneously reducing human operator bias. Conclusions Nymphstar is a fast, accurate image analysis screening tool for the automated counting of nymphs and quantification of leaf area they occupy, allowing for the assessment of cassava resistance to whitefly on a large number of cassava plants in a glasshouse-based assay while avoiding the potential bias normally associated with field assessment and manual counting.

Plant phenotyping relevance

カッサバ葉上のコナジラミ抵抗性を、画像解析で幼虫数と占有葉面積として定量する手法を開発し、手動計数とのベンチマーク検証および抵抗性評価に適用しているため、植物フェノタイピング手法が中心である。

Code and data availability

The paper describes the Nymphstar ImageJ plugin, leaf image acquisition, and phenotype data (Additional file 1), but no block provides an authors' public URL, deposit, or availability statement for the plugin, images, or data. The only URL-like reference (hal.inria.fr/inria-00515624) is a cited prior work, not a paper-

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