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Effect of Phosphorus Nutrition on Response of Perennial Ryegrass Cultivars to Maleic Hydrazide¹

Previously perennial ryegrass, Lolium perenne L., cultivars were found to differ in response to soil treated with maleic hydrazide (l,2-dihydro-3,6-pyridazinedione). However, several cultivars were similar in response to the chemical and results varied from one experiment to the next. The investigation reported here was conducted to improve precision and reliability of cultivar purity tests in which maleic hydrazide (MH) is used. Sand-nutrient culture was used to eleminate soil type as a variable. Every 4th day seedlings were supplied either with a complete nutrient solution or with a solution lacking phosphorus. After the first 12 days, flats on which the solution lacking P was used were supplied with a complete nutrient solution. Starting 18 days after planting, a 300 ppm MH solution was applied to the sand every 4th day. Photoperiods were 8 hours and temperature was 25 C during light periods and 16 C during dark periods. Upper leaf blades started to become chlorotic 12 days after MH treatment was started and cultivars differed markedly. Cultivar differences were greater for plants grown without P the first 12 days than for plants grown with complete solution the entire experiment. The upper leaf blade of most ‘NK-200’ plants became yellow but the next lower leaf blade remained green. In contrast, both upper and second leaf blades of ‘Manhattan’ plants tended to remain green. Second leaf blades of ‘Pennfine’ plants tended to become chlorotic at about the same rate as upper leaf blades. This procedure resulted in greater contrast between cultivars than was obtained in previous experiments. A series of ten experiments demonstrated that very similar results can be obtained from one experiment to the next.

Key Words: Lolium perenne L. • Growth chamber • Chlorosis • Leaf blade • Cultivar purity

² Professor and research support specialist.

Received for publication October 8, 1976.