Relative susceptibility of sunflower maintainer lines and resistance sources to natural infestations of the banded sunflower moth (Lepidoptera: Tortricidae)

Abstract

The banded sunflower moth, Cochylis hospes Walsingham (Lepidoptera: Tortricidae), is a significant seed-feeding pest of sunflowers (Helianthus Linnaeus; Asteraceae) in North America. Though some wild Helianthus, interspecific crosses, and H. annuus Linnaeus cultivars (which precede hybrid sunflower breeding) have low susceptibility to banded sunflower moth, no apparent effort has been made to evaluate modern inbred lines as a source of resistance for hybrids. In field trials from 2013 to 2015, inbred maintainer (HA) lines, resistant accessions (PI), and unreleased, partially inbred (F6) lines were evaluated in field trials using natural infestations of banded sunflower moth. Results show greater seed damage to maintainer lines than the other groups, but also significant variability among lines within groups. The best maintainer, HA 207, had ≈75% fewer damaged seed than the most susceptible HA lines. Among the resistant PI and unreleased inbred lines, only one entry had significantly less damage than HA 207. While PI 494859 showed banded moth resistance superior to the best inbred lines, its other agronomic liabilities make breeding with the least susceptible maintainer lines appear more practical. A key unknown for any attempts to breed hybrids resistant to banded sunflower moth is how closely damage is correlated between inbred lines and their hybrids.

Cochylis hospes (Lepidoptera: Tortricidae) damage to male lines varies significantly and inbred susceptibility predicts damage to hybrids

“…After plants reached physiological maturity, heads were harvested, dried, threshed, and seed samples rated as described in Prasifka and Hulke (2016). In brief, five heads (= subsamples) per plot were collected and dried using forced air at 45°C.…”

“…Based on results from 2013 to 2014, the least damaged male inbred line, RHA 266, was selected as a common parent for a panel of hybrids including all of the publicly released material tested by Prasifka and Hulke (2016), except HA 458 (which has no isoline with cytoplasmic male sterility (cms)). Hybrid seed was produced by growing cytoplasmic male-sterile lines in a greenhouse and pollinating the head of each female with RHA 266.…”

“…First, Dunnett's test used the least damaged hybrid, cms HA 207 × RHA 266, as the control for two-tailed comparisons. Second, to test if C. hospes damage to inbred lines predicted damage to hybrids with a common male parent, the least-squares estimated means for 2016-2017 were regressed onto the corresponding data for female lines as presented in Prasifka and Hulke (2016).…”

“…Additional recent screening has supported the idea that some public inbred lines may have relatively low susceptibility to C. hospes. Field trials with female lines released by the United States Department of Agriculture, Agricultural Research Service showed fourfold differences in seed damage (Prasifka and Hulke 2016), with the least damaged lines statistically similar to some putative resistance sources from Charlet et al (2009). While the causes of reduced susceptibility in female lines identified by Prasifka and Hulke (2016) are unclear, substantial variation exists for both physical (pericarp or "hull" strength; Prasifka et al 2014) and chemical defences (terpenoid compounds in glandular trichomes: Prasifka 2015; Prasifka et al 2015) that are thought to limit damage by larvae of the sunflower moth, Homoeosoma electellum (Hulst) (Lepidoptera: Pyralidae), another floretfeeding and seed-feeding pest of sunflower.…”

“…Though several female lines have low susceptibility to C. hospes, it is unclear whether this quality is also present in male lines and whether damage to inbred lines can be used to predict susceptibility of hybrids. To address these concerns, seed damage from C. hospes larvae was evaluated in field trials using natural infestations for (i) male inbred lines and (ii) hybrids produced from females tested by Prasifka and Hulke (2016) and a common male parent.…”