Impact of Epichloë endophytes on adult Argentine stem weevil damage to perennial ryegrass seedlings

Abstract

In New Zealand, the fungal endophyte Epichlo€ e festucae var. lolii Latch, Christensen & Samuels (Hypocreales) is widely used to enhance productivity and survival of mature perennial ryegrass, Lolium perenne L. (Poaceae) plants. These endophytes produce alkaloids that reduce damage by insect pests, such as Argentine stem weevil (ASW), Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae). However, knowledge of the effect of these fungi on seedlings is limited. High concentrations of grass-endophyte-derived alkaloids occur in endophyte-infected seed and can be translocated into seedlings to provide early protection from insect herbivory. A glasshouse experiment was conducted in which adult ASW were given a choice between perennial ryegrass cultivar 'One50' without endophyte (Nil) or containing endophyte strains AR1, AR37, or NZ CT , and cv. 'Trojan' containing strain NEA2, in three post-sowing time periods. ASW feeding damage was assessed together with plant survival and dry weight production. Plant survival and dry matter production was reduced in all treatments with mortality highest in endophyte-free and AR37 treatments, especially in the first and second time period. Strongest adult ASW deterrence occurred on seedlings infected with endophyte strains that produce peramine (AR1, NZ CT , and NEA2). Strain NZ CT was virtually undamaged in the third time period whereas damage initially increased in AR1 and NEA2 up until day 50-53 post-sowing and then declined. Endophyte-free and AR37 treatments were significantly more damaged than AR1, NZ CT , and NEA2. This research indicated there is a period of seedling vulnerability to adult ASW attack during germination, even for strains producing peramine. Possible explanations for these results are discussed.

Quantifying the economic cost of invertebrate pests to New Zealand’s pastoral industry

“…The entire 370,000 ha of new pasture sown in New Zealand annually is at risk of ASW attack. Even if endophyte-infected ryegrasses are sown the endophyte cannot protect the seedling for the first 4-6 weeks after germination (Ruppert et al 2017). To protect these seedlings, and thereby ensure establishment of high-quality pasture, the use of insecticide seed coatings is estimated to cost $23.7 to $29.6 M or with conventional insecticide, $14.1 M to $24.4 M (2012).…”

“…increased estimate of ASW damage, in the absence of biological control, is at the lower end of the Prestidge et al's (1991) range, taking into account the ongoing progress in the development of grass resistance to ASW based on novel endophytes. However, this useful effect of endophyte is being somewhat offset, by industry shifts towards using more ASW-susceptible short rotation grasses (Goldson et al 2017), the limited extent of endophyte protection of seedling grasses (Ruppert et al 2017) and the generally widespread intensification of New Zealand pastoral farming.…”

Epichloë Fungal Endophytes—From a Biological Curiosity in Wild Grasses to an Essential Component of Resilient High Performing Ryegrass and Fescue Pastures

“…[ 264 ]. For protection against Argentine stem weevil, NEA2, which produces peramine has shown some resistance in the diploid cultivar Trojan [ 437 ], but little protection when in tetraploid cultivar Bealey [ 248 , 431 , 438 ]. Endo5 provides good protection against Argentine stem weevil, African black beetle, pasture mealybug [ 248 ], and root aphid [ 264 ], but not against grass grub [ 248 ].…”

Ontogenetic and trans‐generational dynamics of a vertically transmitted fungal symbiont in an annual host plant in ozone‐polluted settings

“…In addition, there is a strong genetic component controlling the survival of endophytes in seed, explaining some of the observed differences in endophyte status within grass populations (Gundel et al, 2010;Hill & Roach, 2009;Tian et al, 2013). Although the majority of studies investigating endophyte-derived alkaloids are concerned with the vegetative plant, this function has also been linked to the protection of reproductive structures and the seed (Faeth, 2009;Finch, Pennell, Kerby, & Cave, 2016;Pennell et al, 2017;Uchitel, Omacini, & Chaneton, 2011), which can extend to protection of the developing seedling (Gundel, Rudgers, & Whitney, 2017;Gundel, Seal, et al, 2018;Justus, Witte, & Hartmann, 1997;Ruppert, Matthew, McKenzie, & Popay, 2017;A. V. Stewart, 1985).…”