Relationship between Colonization by Onion Thrips (Thrips tabaci Lind.) and Leaf Colour Measures across Eight Onion Cultivars (Allium cepa L.)

Maria Pobożniak,Marta Olczyk,Tomasz Wójtowicz

doi:10.3390/agronomy11050963

Maria Pobożniak, Marta Olczyk + Show 1 more

Open Access

https://doi.org/10.3390/agronomy11050963

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Abstract

Thrips tabaci Lindeman is a global pest and also represents a serious threat to onion production in Poland. In 2 years (2015–2016) of field studies, 8 onion cultivars were evaluated to characterize their susceptibility to onion thrips and to determine if leaf colour is associated with thrips preference. The actual count and the proportional abundance of adult thrips collected from onion leaves during plant colonization by insects were both used to express the preference of thrips for different onion cultivars. At the same time, the colour measurements were analysed by considering the CIELAB (CIE 1976 L*a*b*) and CIE L*C*h* colour spaces. There were distinct differences in the susceptibility of onion cultivars to colonization by onion thrips. Leaf colour coordinate values were correlated with attractiveness to thrips; typically, higher lightness (L*), yellowness (b*), chroma (C*), hue (h*), and lower redness (a*) attracted more thrips. We concluded that the vivid, intense green-yellowish leaf colour of susceptible varieties might have been the cause of the thrips preference observed. We also identified useful genotypes, Tęcza and Wenta, for host plant resistance to thrips and suggest a link between colour and antixenotic resistance. The resistant cultivars had darker, green-grey-yellowish leaves.

Highlights

We report the result of measuring the susceptibility of existing commercial onion cultivars to T. tabaci infestation concerning leaf colour characteristics
Addition, the the actual actual count count and and proportional proportional abundance of thrips collected from onion plants with a sweeping net were significantly abundance of thrips collected from onion plants with a sweeping net were significantly affected
We found distinct differences in some computed colour variables between the leaves of the onion cultivars most and least susceptible to T. tabaci infestation, but because of the discrepancy in the results between the two years of the study, the role of visual cues for thrips must be interpreted with caution

Summary

Introduction

Larvae and adults of onion thrips live in the leaf sheath and chives, and their feeding causes silvery leaf spots that turn into white blotches along the leaves due to the removal of cellular content. This injury reduces photosynthetic ability and interferes with the transportation of nutrients to the bulb [6]. The negative effects of onion thrips are reflected in both the quantity and quality of the crop [7] Their feeding causes the reduction of onion bulb mass and has an indirect effect by creating an entry point for plant pathogens [8,9]. Effective control of onion thrips necessitates frequent applications of insecticide [11], with the unfortunate result of increased resistance to commonly used chemicals [12,13]

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