Abstract
Capsicum is a genus containing important crop species, many of which severely suffer from thrips infestation. Thrips feeding damages leaves and fruits, and often results in virus infections. Only a few insecticides are still effective against thrips, underlining the importance of finding natural resistance in crops. Capsicum is a perennial plant which is usually cultivated for several months, during which time the fruits are harvested. From the young vegetative stage to the mature fruit bearing stage, the plants are at risk to thrips infestation. Constitutive resistance to thrips over the entire ontogenetic development is therefore a key trait for a more sustainable and successful cultivation of the hot and sweet pepper. In addition to ontogeny, leaf position can affect the level of thrips resistance. Pest resistance levels are known to differ between young and old leaves. To our knowledge, no studies have explicitly considered ontogeny and leaf position when screening for constitutive resistance to thrips in Capsicum. In this study we analyze whether ontogeny and leaf position affect leaf-based resistance to Frankliniella occidentalis and Thrips tabaci, in 40 Capsicum accessions, comprising five different species. Our results show that resistance to both thrips species in Capsicum varies with ontogenetic stage. This variation in resistance among ontogenetic stages was not consistent among the accessions. However, accessions with constitutive resistance in both the flowering and fruit ripening stage could be identified. In addition, we found that thrips resistance is overall similar at different leaf positions within the ontogenetic stage. This implies that resistance mechanisms, such as defense compounds, are constitutively present at sufficient levels on all leaf positions. Finally, we found that resistance to F. occidentalis and resistance to T. tabaci were not correlated. This indicates that leaf-based resistance in Capsicum is thrips species-specific. Because of the variation in resistance over ontogeny, identifying Capsicum accessions with resistance over their entire lifespan is challenging. For resistance screening, accounting for leaf position may be less of a concern. To identify the defense mechanisms responsible for thrips resistance, it is important to further analyze and compare resistant and susceptible accessions.
Highlights
Thrips are wide-spread piercing-sucking insects which are responsible for severe yield reduction in vegetable crops such as cucumber, strawberry, melon and pepper (Shipp et al, 2000; Park et al, 2007; Peng et al, 2011; Sampson and Kirk, 2013)
There was a strong effect of ontogeny, we identified several C. annuum and C. chinense accessions with consistent constitutive leaf-based resistance in the flowering and fruit ripening stage
We further demonstrate that when the plant is in a certain ontogenetic stage, resistance scores are mostly similar at different leaf positions
Summary
Thrips are wide-spread piercing-sucking insects which are responsible for severe yield reduction in vegetable crops such as cucumber, strawberry, melon and pepper (Shipp et al, 2000; Park et al, 2007; Peng et al, 2011; Sampson and Kirk, 2013). Crops infected with thrips show stunted growth, leaf deformation and scarring of the fruits, leading to reduced yield and marketing quality (Welter et al, 1990; Tommasini and Maini, 1995; Shipp et al, 1998) They are an important vector of plant viruses, especially tospovirsuses (Whitfield et al, 2005; Riley et al, 2011; Rotenberg et al, 2015). Thrips control is mostly achieved by integrated pest management (IPM) (Weintraub, 2007; Mouden et al, 2017), which combines chemical and biological strategies to grow healthy crops (Ehi-Eromosele et al, 2013) Pesticides have lost their effectiveness due to the emergence of resistant thrips populations (Bao et al, 2014; Li et al, 2016; Nazemi et al, 2016). The successful application of IPM to minimize pesticide use is dependent on the presence of natural resistance in crop plants
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