Susceptibility and tolerance in hybrid and pure-line rice varieties to herbivore attack: biomass partitioning and resource-based compensation in response to damage

Abstract

Hybrid rice has been noted for its susceptibility to insects and diseases compared to pure-line (conventional) rice varieties. We investigated herbivory by Nilaparvata lugens, Sogatella furcifera and Scirpophaga incertulas on replicated three-line hybrid sets (parental and hybrid lines) in field and greenhouse experiments. In a field experiment, caterpillar densities and stemborer damage was similar among hybrid and parental lines. In field and greenhouse experiments, the cytoplasmic male sterile (CMS)-lines and maintainer lines had higher densities of planthoppers (including N. lugens and S. furcifera) than restorer or hybrid lines likely because of their wild abortive CMS-lineage. High nitrogen levels increased plant mortality due to N. lugens, but often reduced mortality from S. furcifera and S. incertulas: this was similar between hybrid and pure-line varieties. The hybrids were generally more tolerant of herbivory (lower biomass reductions per unit weight of insect) than the inbred parental lines. The addition of nitrogen to both the hybrid and pure-line varieties had contrasting effects on tolerance depending on the nature of the attacking insect: fertiliser increased tolerance to S. furcifera (lower losses of yield and shoot biomass per mg insect) and S. incertulas (lower yield, shoot and root biomass loss) but fertiliser reduced tolerance to N. lugens (higher loss of root biomass and no effects on yield and shoot biomass loss). Our results indicate that hybrid rice is not physiologically more susceptible to herbivores than are pure-line varieties even under high nitrogen conditions, but does have higher tolerance to insect damage.

Integrated pest management for sustainable rice cultivation: a holistic approach

“…However, they also become notably more attractive to pests and more susceptible to a variety of diseases (Horgan and Crisol, 2013;Horgan et al, 2016a;Hu et al, 2016). Field and laboratory studies have indicated higher levels of damage from insects, snails and weeds to rice produced under high nitrogen conditions (Eggum and Juliano, 1973;Ampong-Nyarko and Datta, 1993;Hu et al, 2016).…”

“…Rice plants under high nitrogen are predicted to better tolerate damage (can compensate for biomass loss) depending on the nature of the attacking herbivore or parasite (Horgan et al, 2016a;Prot et al, 1994). For example, yield losses to rice from certain insect herbivores can be avoided by treating affected plants with high nitrogen (Jiang and Cheng, 2003;Inthavong et al, 2004).…”

“…Several hybrid rice varieties, particularly varieties with a wild abortive cytoplasmic male sterile (WA-CMS) parent, have noted susceptibility to the white-backed planthopper (Sogatella furcifera [Horvath]: Delphacidae: Homoptera) and green leafhoppers (Nephotettix spp.) (Cicadellidae: Homoptera) (Sogawa et al, 2003;Horgan et al, 2016a). This includes an estimated 40% of modern hybrid varieties and most Chinese-bred hybrids (Horgan and Crisol, 2013).…”

“…However, hybrid rice may be more tolerant of herbivore damage, which represents a major advantage for natural pest regulation in well-managed rice production systems, but also a potential drawback because it creates a reservoir for diseases, including insectvectored rice viruses (Horgan, 2012;Horgan et al, 2016a). Knowledge of the weaknesses of hybrid rice has led researchers to seek new sources of male sterility without associated planthopper susceptibility (Horgan and Crisol, 2013); however, faster growth rates and the nutrient demands of hybrids may continue to make these more attractive to herbivores (Price, 1991;Horgan et al 2016a).…”

“…Knowledge of the weaknesses of hybrid rice has led researchers to seek new sources of male sterility without associated planthopper susceptibility (Horgan and Crisol, 2013); however, faster growth rates and the nutrient demands of hybrids may continue to make these more attractive to herbivores (Price, 1991;Horgan et al 2016a).…”