Field tolerance to pasture dieback of 26 tropical grass varieties sown into an affected paddock

Abstract

Pasture dieback is a condition where tropical grass pastures show stress symptoms (yellowing, reddening, wilting, poor growth) followed by death in patches that expand over time. Multiple potential causal agents have been identified in association with pasture dieback but the cause has not been demonstrated. A wide range of sown pasture grass species have been reported as being affected by pasture dieback although the severity varies between species and locations. Twenty-six varieties of grass across fifteen species were sown in February 2020 into a paddock where Rhodes grass had been severely affected by dieback in 2018-2019. Poor growth, stress systems and plant death in patches that are characteristic of pasture dieback occurred during the first growing season and all varieties had very poor root system development. Multiple potential causal agents were present at the site including novel viruses, nematodes and ground pearl (Margarodes australis) but no pasture mealybug (Heliococcus summervillei), which has been postulated as the primary causal agent of pasture dieback by some researchers.