The effects of cutting time and post-cutting rainfall on perennial ryegrass seed endophyte survival and seed quality: A dissertation submitted in partial fulfilment of the requirement for the Degree of Bachelor of Science with Honours

Abstract

Novel endophyte technologies are now a widely accepted part of modern pastoral agriculture within New Zealand, owing to their production of alkaloids which have been shown to significantly reduce the effects of pasture pests and therefore increase pasture productivity without affecting animal health. As a result, production of endophyte infected seed has significantly increased, with Canterbury being the major region of production. At harvest, seed crops are cut and left in the swath for seeds to dry before combining, but there can sometimes be significant rainfall over the natural drying period. Therefore, this trial was set up to observe the effects that this rainfall has on both seed quality and endophyte viability.

A perennial ryegrass (cv. Samson) seed crop was cut at either 50% seed moisture content (SMC) or at 40% SMC. For the 50% SMC cutting time (CT), all plots received 50.2mm of rain over the 35 days post-CT, with additional irrigation to simulate rainfall supplying 30mm for three treatments and 45mm for one treatment. All 40% SMC CT plots received 41.5mm rain, plus the 30mm for three treatments and 60mm for one treatment. Seed heads were randomly hand sampled from the swath beginning at 10 days after cutting (DAC) and continued twice weekly up to 35 DAC. Seed heads were dried, threshed, and seeds dressed and tested. Seed quality was assessed by seedling emergence in potting mix, and endophyte viability determined using ELISA (Enzyme linked immunoblot assay).

For the 50% SMC CT emergence remained steady at around 90% for all simulated rainfall treatments and sampling dates between 10 and 21 DAC, but then began to decline reaching ca. 82% by 33 DAC. There were no significant differences among treatments. In the 40% SMC CT emergence fell between 10 and 21 DAC (from 90% to between 75 - 80%), and continued to fall between 21 and 33 DAC, at which time the emergence for the control (82%) was significantly greater than that for the 'Late 30mm' simulated rainfall and the 'Full Wet - 60mm' simulated rainfall treatments.

Viable endophyte levels were around 85% at 10 DAC for the 50% SMC CT, and had declined to around 75% by 33 DAC for all treatments. Similar declines were recorded for the 40% SMC CT, where there were no significant differences among treatments. However, the rate of decline in endophyte viability was lower for the 40% SMC CT (-0.3% dai1) than for the 50% SMC CT (-0.5% dai1). Conversely, the rate of emergence decline was greater for the 40% SMC CT than the 50% SMC CT. As there was substantial natural rainfall over the drying period, all the control plots received rain, and as a result, there were very few differences between the control treatments and the simulated rainfall treatments for either seed emergence or endophyte viability. As the effects of post-cutting rainfall could therefore not be accurately determined, the experiment should be repeated, preferably using rain shelters.