The effect of sowing date, seed size and disease on the establishment of Domino wheat: A dissertation submitted in partial fulfilment of the degree of Bachelor of Agricultural Science with Honours at Lincoln University, New Zealand

Abstract

The focus of this study was to investigate the relationships between sowing date, seed size and disease, on the emergence of Domino wheat. Two seed lines of Domino wheat containing 18 and 90 % diseased seed (infected with Microdochium nivale formerly Fusarium nivale) were sown on 6 May, 20 May, 13 June and 26 July. Each seed line was split into three seed sizes (35 mg, 44 mg and 55 mg seed) and five hundred seeds were sown per plot. Disease reduced final emergence by up to 30 % (150 plants) when soil temperatures dropped below 8 °C. At temperatures above 8 °C disease did not affect emergence. Delaying sowing from 6 May until 13 June caused an increase of nine days from sowing until initial emergence. This slowing in the rate of plant emergence enable the disease to attack the seedling which reduced emergence. When time to emergence was quantified using thermal time all sowings emerged at the same rate with 50 % emergence occurring at 125 °C days after sowing. Phyllochron was also constant at 101 °C days or 0.0084 leaves/°C day for all sowing dates. Seed size did not interact with sowing date or disease. Large seed (55 mg) consistently gave an increase of 20 % emergence over bulk ( 44 mg) seed. Bulk ( 44 mg) seed consistently established 30% more seedlings than the small (35 mg) seed. When high diseased seed was treated with Baytan IM emergence percentages above 90 % were achieved compared with 70 % for untreated seed. Untreated seed is not generally sown in New Zealand except in organic farming systems. Results of the present study suggest that early sowing (early May) is required to avoid disease damage and achieve maximum establishment. Organic growers are however left with the conundrum that early sown crops are highly likely to be infected with the aphid transmitted barley yellow dwarf virus. For conventional farmers using chemically treated seed this study has shown that delaying sowing from May to July has no effect on emergence. The thermal time concept has also allowed the data obtained in the present study to be used to predict times to emergence in other regions in New Zealand.