Development and application of a quantitative bioassay to evaluate maize silk resistance to corn earworm herbivory among progenies derived from Peruvian landrace Piura

Abstract

Corn earworm (CEW), Helicoverpa zea (Boddie), (Lepidoptera: Noctuidae), is a major insect pest of corn ( Zea mays spp. mays L.). CEW larvae feed on silks, kernels and cobs, causing substantial yield and quality losses both through herbivory and by vectoring pathogens. The long-term goal of this work is to elucidate the genetic and biochemical basis of a potentially novel CEW resistance source discovered in silk tissue of Piura 208, a Peruvian landrace of maize (PI 503849). We developed a quantitative CEW bioassay and tested it on four populations that contrast alleles from Piura 208 with those from GT119, a CEW-susceptible maize inbred line. In replicated analyses of two populations of F 1:2 families, corn genotype accounts for 84% and 68% of the variance in CEW larval weights, and up to 60% of the variance in CEW pupation percentage, demonstrating both the success of the quantitative bioassay and the strength of the Piura 208 resistance mechanism. Analyses of two corresponding populations of BC 1:2 families revealed substantially diminished effects of corn genotype on CEW weight gain and pupation. This loss of Piura 208-derived CEW resistance during backcrossing suggests complex (multi-genic) inheritance of a threshold-dependent mechanism. Technical factors in bioassay performance were also assessed, often by analyzing the 1,641 CEW larvae that were raised on control diet (meridic with no corn silks added). Minor, but statistically significant impacts on CEW weight gain, pupation, and mortality were attributable to multiple technical factors in the preparation, incubation and evaluation phases of the bioassay, demonstrating the importance of randomization, stratification, replication, and variable-tracking across the many steps of this quantitative CEW bioassay. Overall, these findings indicate that this scaled-up, quantitative CEW bioassay is fundamentally sound and that Piura 208-derived resistance alleles are experimentally tractable for genetic and mechanistic research using this approach.

A multigenotype maize silk expression atlas reveals how exposure‐related stresses are mitigated following emergence from husk leaves

“…This, in turn, requires silks to use physical and biochemical mechanisms to guard against the water deficits, pathogens, and pests that are typical of midsummer (Ortega Corona, 1987; Pechanova & Pechan, 2015). Indeed, silks exhibit a high level of phenotypic variability in emergence rates across diverse germplasm under drought (Bolaños & Edmeades, 1996), as well as differences in susceptibility to different pathogens (Lübberstedt, Klein, & Melchinger, 1998) and pests (Abel, Wilson, Wiseman, White, & Davis, 2000; Lopez et al., 2019). Moreover, the composition of many specialized metabolites varies among cultivars, including maysin (Byrne et al., 1996; Szalma, Buckler, Snook, & McMullen, 2005) and cuticular lipids (Dennison et al., 2019; Loneman et al., 2017; Perera et al., 2010).…”

Mechanistic dissection of stress mitigation imparted by the maize epidermis

“…This in turn requires that silks use physical and biochemical mechanisms to guard against water deficits, pathogens and pests that are typical of mid-summer (Alejandro Ortega, 1987;Pechanova & Pechan, 2015). Indeed, silks exhibit a high level of phenotypic variability across diverse germplasm in emergence rates under drought , as well as in susceptibilities to different pathogens (Lübberstedt, Klein, & Melchinger, 1998) and pests (Abel et al, 2000;Lopez et al, 2019).…”