Abstract
We tested the hypotheses that increasing the number of anti-herbivore resistance loci in crop plants will increase resistance strength, increase the spectrum of resistance (the number of species affected), and increase resistance stability. We further examined the potential ecological costs of pyramiding resistance under benign environments. In our experiments, we used 14 near-isogenic rice lines with zero (T65: recurrent parent), one, two or three resistance loci introgressed through marker-assisted selection. Lines with two or more loci that were originally bred for resistance to the green rice leafhopper, Nephotettix cincticeps, significantly reduced egg-laying by the green leafhopper, N. virescens. Declines in egg-number and in nymph weight were correlated with the numbers of resistance loci in the rice lines. To test the spectrum of resistance, we challenged the lines with a range of phloem feeders including the zig-zag leafhopper, Recilia dorsalis, brown planthopper, Nilaparvata lugens, and whitebacked planthopper, Sogatella furcifera. There was an increase in the number of tested species showing significant declines in egg-laying and nymph survival on lines with increasing numbers of loci. In a screen house trial that varied rates of nitrogenous fertilizer, a line with three loci had stable resistance against the green leafhopper and the grain yields of infested plants were maintained or increased (overcompensation). Under benign conditions, plant growth and grain yields declined with increasing numbers of resistance loci. However, under field conditions with natural exposure to herbivores, there were no significant differences in final yields. Our results clearly indicate the benefits, including unanticipated benefits such as providing resistance against multiple herbivore species, of pyramiding anti-herbivore resistance genes/loci in crop plants. We discuss our results as part of a review of existing research on pyramided resistance against leafhoppers and planthoppers in rice. We suggest that potential ecological costs may be overcome by the careful selection of gene combinations for pyramiding, avoidance of high (potentially redundant) loci numbers, and introgression of loci into robust plant types such as hybrid rice varieties.
Highlights
Recent advances in marker-assisted selection for food and fibre crops have streamlined breeding programs (Bourke et al, 2018; Garrido-Cardenas et al, 2018) and given new insights into the ecological and evolutionary relations between plants and components of their environment (O'Rourke et al, 2014; Odjo et al, 2017)
GLH nymphs had lower survival and nymph biomass on GRH2/ GRH4-PYL and GRH2/GRH4/GRH6-PYL compared to Taichung 65 (T65) (P < 0.05, Dunnett's test, Table 1)
Compared to T65, egg-laying by GLH was lower on qGRH4-near-isogenic lines (NILs), GRH2/GRH4-PYL, GRH2/GRH5-PYL, GRH2/GRH6-PYL and on GRH2/ GRH4/GRH6-PYL, (Table 1)
Summary
Recent advances in marker-assisted selection for food and fibre crops have streamlined breeding programs (Bourke et al, 2018; Garrido-Cardenas et al, 2018) and given new insights into the ecological and evolutionary relations between plants and components of their environment (O'Rourke et al, 2014; Odjo et al, 2017). A range of phloem-feeding insects, including leafhoppers (e.g., the green rice leafhopper [GRH], Nephottetix cincticeps, and green leafhopper [GLH], N. virescens) and planthoppers (e.g., the brown planthopper [BPH], Nilaparvata lugens, and whitebacked planthopper [WBPH], Sogatella furcifera), currently challenge rice production in Asia. These species can cause severe yield reductions to intensified rice agroecosystems, where farmers are encouraged to use high rates of nitrogenous fertilizer and prophylactic insecticide applications (Bottrell and Schoenly, 2012; Crisol et al, 2013). Despite the tremendous investments into pyramiding herbivore resistance genes/loci, surprisingly few researchers have tested these hypotheses using available near-isogenic materials
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
