Ryegrass virus research re-visited

A novel science project at Barenbrug in Canterbury has cast new light on a pasture challenge that has not been widely investigated since the 1970s.


As part of the company’s research programme, the project compared different populations of the same ryegrass cultivars to see if virus diseases built up over time within the plants to levels that would affect DM yield.


Barenbrug science manager Colin Eady says in this experiment, the short answer was yes, they did. Older plants with more disease averaged 20% less DM than younger plants with less disease.


This project was used for a Masters’ thesis by Lincoln University student Maxine Farquhar and is one of several Masterates that Barenbrug is involved with.


It stemmed from Colin’s interest in pasture persistence and his previous research on other plant crops which, like ryegrass, reproduce sexually and asexually. Over time, virus is known to affect yields of crops which only reproduce asexually.


Thanks to a long-standing field trial on the Barenbrug research farm, Maxine was able to find tillers of 10 year old ryegrass plants that were genetic copies of the original parent sown, and compare these with tillers from new seedlings of the stored original seed.


Each set of young vs old plants was established in the glasshouse before being transplanted to the field for DM yield cuts over a growing season. From the start, Colin says, differences were immediately obvious, and mowing ultimately showed old plants derived from clonal daughter tillers averaged 20% less DM than those grown from the stored seed.


Maxine’s quantitative molecular analysis likewise showed old plants had much higher levels of virus than the newly germinated ones.


Colin says although viruses in ryegrass are not well understood, it is believed to be one factor that reduces pasture performance on farm over time. “What we’ve shown in this instance is that old pastures are quite capable of living with virus, but they’re probably not going to yield as much biomass as newer pasture - regardless of the cultivar.”