Nitrogenous Fertilizer Reduces Resistance but Enhances Tolerance to the Brown Planthopper in Fast-Growing, Moderately Resistant Rice

Abstract

The brown planthopper, Nilaparvata lugens (Stål), is a key challenge to rice production in Asia. Outbreaks of planthoppers are associated with excessive fertilizer applications; consequently, we examined planthopper interactions with susceptible, tolerant and resistant varieties of rice under varying levels of soil nitrogen in a greenhouse experiment. We compared planthopper fitness (survival × reproduction) and plant tolerance (functional plant loss index) for 16 varieties at 0, 80 and 150 Kg added nitrogen ha^-1. The planthoppers grew larger, developed more quickly and laid more eggs on susceptible varieties, compared with the resistant and tolerant varieties. Moreover, soil nitrogen generally increased planthopper fitness on resistant varieties, but relative resistance was maintained. Functional plant loss was highest among the susceptible varieties, but weight and growth rate reductions per mg of planthopper were often highest in the tolerant varieties. Tolerance was associated with large, fast-growing plants, with at least moderate resistance to the planthopper. Susceptibility was associated with a small size and/or an absence of resistance genes. Our results suggested that early-tillering rice plants can be both resistant and tolerant to the brown planthopper, but cannot be both susceptible and tolerant of planthoppers at high densities. This indicates that at least moderate resistance is required for tolerance against this herbivore. Furthermore, although dwarf varieties had a low tolerance of planthoppers, they could express resistance through functioning resistance genes.

Keywords: BPH3; BPH32; Nilaparvata lugens; Sogatella furcifera; compensation; phenotyping; phloem feeding; sustainable agriculture; xylem.

Figure 1

(A) FPLI for 16 varieties/lines at three nitrogen levels, with (B) changes in plant growth rate between 30 and 45 DAS under three levels of soil nitrogen after infestation with planthopper nymphs and (C) corresponding growth rate changes per mg of planthopper. Error bars are indicated (N = 3). Lowercase letters indicate homogenous variety groups (Tukey p > 0.05).

Figure 2

Relations between plant growth rate and (A) plant weight loss, and (B) weight loss per mg of planthopper for 16 rice varieties exposed to planthoppers under three nitrogenous fertilizer regimes (see legend). Each point is the average of three replicates. Best-fit linear models are indicated for each nitrogen level (Table 3).

Figure 3

Canonical Analysis of Principal Coordinates (CAP) depicting differences in herbivore fitness and plant damage parameters obtained through multiple bioassays. Squares represent resistant varieties/lines, whereas circles represent susceptible varieties/lines. Nitrogen regimes (1 = 0 added N, 2 = 80 Kg N ha⁻¹, and 3 = 150 Kg N ha⁻¹) are represented by increasing color darkness. Overlayed vectors (in blue) represent the correlations (Pearson’s correlation coefficient > 0.6) between rice lines and the CAP axes, where vector length and direction reflect the increasing values of correlation and parameter values, respectively.