Do Rice Hybrids Have Heterosis for Insect Resistance? A Study with <I>Nilaparvata lugens</I> (Hemiptera: Delphacidae) and <I>Marasmia patnalis</I> (Lepidoptera: Pyralidae)

Abstract

Antibiosis-based resistance to two insect pests of rice, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae) and Marasmia patnalis Bradley (Lepidoptera: Pyralidae), was compared in 11 F1 hybrids and their parental lines. Our objective was to determine whether hybrids show heterosis (hybrid vigor) for insect resistance or susceptibility. Heterosis is defined as the amount by which a hybrid exceeds its midparent value or its better parent. Overall, we did not find evidence of heterosis or heterobeltiosis (a type of heterosis in which a hybrid exceeds its better parent) for antibiosis-based resistance or susceptibility to either of the insects. One hybrid, IR64616H, seemed more resistant to M. patnalis than its better parent but none of the other hybrids showed heterobeltiosis for resistance or susceptibility to either insect. Three hybrids had resistance to N. lugens that exceeded their midparent value, possibly due to dominant resistance in one of the parents. The increased frequency and severity of insect outbreaks on hybrid rice that have been reported in China may be attributable to factors other than diminished antibiosis in hybrids, such as greater attractiveness of hybrids to migrating or dispersing insects or differences in agronomic practices applied to hybrids and inbred rice cultivars.

Heterosis for Resistance to Insect Herbivores in a 3-Line Hybrid Rice System

“…In our greenhouse experiment with 15 hybrid varieties and their parental lines, we noted that only one A line (IR70369A) was associated with susceptibility to BPH and WBPH in some resulting hybrids. Cohen et al (2003) [ 37 ] found similarly low variability across BPH responses to hybrids and their parental lines using a different range of hybrids from the same breeding program. Susceptibility related to IR70369A was more consistent in our experiments with BPH than WBPH (i.e., other lines derived from IR70369A tended to also have high numbers or a high biomass of BPH, but not of WBPH: Tables S2 and S5 ).…”

“…The B line is required to maintain A line seed. The B line has the same nuclear genome as the A line, but has a distinct cytoplasmic genome that permits the production of viable pollen [5,37]. The restorer lines are more genetically diverse than the A and B lines and are selected based on their ability to combine with the A line to restore fertility [5,16].…”

Heterosis for Interactions between Insect Herbivores and 3-Line Hybrid Rice under Low and High Soil Nitrogen Conditions

“…The B line is required to maintain A line seed. The A and B lines share the same nuclear genome but have distinct cytoplasmic genomes that bestow sterility to the A line [ 5 , 25 ]. We arbitrarily selected the eight hybrids ( Table S1 ) and their associated parental lines from the IRRI breeding program, with no a priori considerations except that a sufficient number of seeds should be available for the experiments.…”

“…Heterosis can be enhanced by increasing the genetic distance between parental lines [ 22 , 23 ]; this will also limit the movement of certain pests, such as planthoppers, between fields with different hybrid rice varieties [ 1 , 24 ]. Breeders can further avoid herbivore-susceptible parental lines and promote specific combinations of parental lines that achieve heterobeltiosis for herbivore resistance [ 11 , 25 , 26 ]. However, there are limitations on the choice of parents for hybrid breeding programs, as not all lines can restore fertility [ 5 , 6 ].…”

“…Furthermore, tolerance to certain pests and diseases can be enhanced under high fertilizer conditions [ 18 ]. Despite its importance, only a few studies have examined heterosis for resistance to rice herbivores in hybrid rice [ 11 , 25 , 26 ]. This is partly because parental lines are generally restricted as intellectual property for commercial use.…”