Survival of endophyte-infected ryegrass seed buried in soil

Abstract

Emergence of volunteer perennial ryegrass (Lolium perenne L.) from seed buried in soil may contribute to the ingress of ryegrass in newly sown pastures. To investigate this, ryegrass seed infected with fungal endophyte (Neotyphodium lolii) was buried in nylon bags under pasture at two depths and at two sites (Palmerston North, Lincoln) in early/mid-autumn 1998. Seed bags were removed from the soil at intervals over the course of one year to determine seed viability and presence of endophyte in seedlings. Viability of seed declined rapidly to be 10% 3 months after burial. Further decline in viability was less, so that 12 months after burial 4% of seeds were still viable. Endophyte viability also declined, from 58% infection of seedlings at the time of burial to 21% at 12 months. This was at a slower rate than the decline in seed viability and from what might have been predicted from seed storage experiments. Viability of seed buried at 10 cm was greater than that buried at 3 cm (e.g., means, 10% and 1% after 6 months, respectively). This has implications for cultivation practices before pasture establishment. Seed buried at Lincoln maintained higher viability than seed buried at Palmerston North (e.g., means, 6% and 4% after 6 months, respectively), which was associated with drier soil conditions at Lincoln. Survival of buried seed may therefore be of greater importance in summer-dry east coast regions, compared with moist west coast environments or in wet years. The significance of buried ryegrass seed will depend on the numbers involved, but after 12 months there were still viable seeds left in the soil and some of these were infected with endophyte. This is important for pastures sown with ryegrass that is free of endophyte or infected with a selected endophyte, and for slower establishing grass species such as tall fescue. Keywords: endophyte, endophyte survival, Lolium perenne, Neotyphodium lolii, perennial ryegrass, seed burial, seed survival