Seed vigour, seedling vigour and seedling establishment of Lotus pedunculatus cav. cv. grasslands maku

Abstract

Initial establishment of Maku lotus at two South Island high country sites was 4.0 and 2.7% compared with about 20% for white clover (Trifolium repens cv. Grasslands Huia) and birdsfoot trefoil (Lotus corniculatus cv. Maitland). Reasons for the poor establishment of Maku were investigated in subsequent glasshouse and laboratory experiments using up to eight Maku seed lots and the seed lots from the field trials.

Germination of Maku was very slow at 12 and 8ºC compared with the other species. There was variation among Maku seed lots for percentage germination (70-94), rate of germination at 20ºC (21-30% day⁻¹), abnormal seedlings (5-20%), hard seeds (0.3-6%), imbibed not germinated seeds (0.5-5%), seedling elongation (30-37 mm after six days at 18-21ºC), electrolyte leakage (257-460 µmhos g⁻¹ of seed) and the ability to germinate at 8ºC (23-40% after 31 days). There was also variability among five seed size categories within the Maku seed lots. Smaller seeds were slower to germinate, had more abnormal seedlings and imbibed not germinated seeds but fewer hard seeds, shorter seedlings in the elongation test and more electrolyte leakage than larger seeds. Conductivity g⁻¹ was well correlated with percentage germination at 20ºC, abnormal seedlings and imbibed not germinated seeds (r = -0.78, 0.76 and 0.73 respectively).

A glasshouse pot trial with five seed sizes of four Maku seed lots indicated that growth until 19 days after sowing was most influenced by emergence rate; by 27 days the effect of seed size was greater. The largest seeds produced 30% more dry matter 31 days after sowing than the smallest seeds. Maku and white clover seed from the field trials was used in a second pot trial to investigate growth at root zone temperatures of 12, 15 and 18ºC. Emergence of Maku was slower than white clover at all temperatures and more affected by a decline in temperature. Growth of Maku between three and six weeks after sowing was similar or superior to white clover. However, after six weeks at 12ºC white clover roots (65 mm) were still longer than Maku (45 mm)

Variability among Maku seed lots indicates that genetic and/or phenotypic factors influence seed quality and deserve investigation. Selection for larger seeds, rapid low temperature germination and seedling vigour would improve establishment. Rate of germination at 12ºC and seedling length after four days at 20ºC should be good indicators of potential field establishment.