Fungicide control of blind seed disease (Gloeotinia temulenta) without affecting AR37 endophyte in ryegrass seed crops : a thesis presented in partial fulfilment of the requirements for the degree of Master of AgriScience in Seed Science and Technology at Massey University, Palmerston North, New Zealand

Abstract

Blind seed disease (BS) is caused by the fungus Gloeotinia temulenta that directly affects the germination of grass seeds by killing the embryo. This disease continues to periodically affect the forage grass seed industry (Alderman, 2001). Epichloë fungal infection has a symbiotic association with grasses, providing beneficial traits to the plant host, having a crucial role in ensuring the persistence of grasses against biotic and abiotic threats (Mortimer and Di Menna, 1982; Popay and Rowan, 1994). This study focuses on new fungicide testing used to control BS and its effects on the transmission of the AR37 endophyte into the new seed generation. In this study, thousand seed weights, germination percentages, blind seed determinations and immunoblot detection of endophyte were carried out to assess the effects of different foliar fungicide treatments used to control blind seed (BS) and other pathogens, on the transmission of the AR37 endophyte into the developing seed of perennial and hybrid ryegrass cultivars (Samson, Horizon and PGone50). Trial one, but not trial two, was conducted on a paddock where there were abundant buried seed with BS disease to ensure a high potential for this disease to develop in the treatments plots. In trial one, germination in Samson with all fungicide treatments used was higher, and conversely BS was lower, than the control (except T12 composed of folpet). The treatments that best controlled BS in Samson were T2 (70% germination, composed by 100 g/ha prothioconazole applied at mid-flowering); T4 (72% germination, composed by 100 g/ha prothioconazole + 250 g/ha carbendazim applied at mid-flowering and mid-seed fill); T8 (73% germination, composed by 125 g/ha azoxystrobin with 189.2 g/ha tebuconazole applied twice (at mid-flowering and mid-seed fill and 250 g/ha carbendazim at mid-seed fill); and T9 (73% germination, composed by 100 g/ha prothioconazole + 75 g/ha isopyrazam + 250 g/ha carbendazim applied at mid-flowering and mid-seed fill). No reduction in endophyte transmission to seed was observed with the fungicide treatments with the exception of the applications of folpet. In turn, with Horizon several fungicide combinations were able to improve the germination performance by controlling BS, however Horizon had a lower performance in terms of controlling BS. The percentage of Horizon seed with endophyte in all treatments was very low, possible reflecting the use of seed with a low percentage of viable AR37 endophyte when the grass seed crop was established some years previously. In trial two, germination, endophyte content, and seed yield between the treatments were not different. All treatments (including the control) had a germination level between 84 to 89%. All treatments used in this trial maintained the AR37 endophyte content in the resultant seed lots. It is known that the application of some fungicides used to control a range of pathogens is detrimental to the viability of endophytes. Therefore, it is imperative that research in the quest of new treatments that control effectively BS without exerting detrimental effects on endophyte continues.