Seed production in garden nasturtium (Tropaeolum majus Linn.) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agriculture Science in Seed Technology at Massey University, Palmerston North, New Zealand
This thesis reports the results of research on seed production of garden nasturtium (Tropaeolum majus). The research programme was begun in late 1991 with an investigation on the effects of plant density on Tropaeolum majus cv. Choice Mixed grown under field conditions. The plant responses to changing plant density in terms
of the vegetative growth and morphology, flowering pattern, seed yield and yield component were investigated using four different densities ranging from 3 to 45 plants per m2• The results of this research showed that increasing plant density decreased branch number, dry weight, leaf number and area, and flower number per plant. It was also shown that seed yield is primarily determined by the number of flowers produced per m2 and this character was identified as an important aspect to be manipulated for improving seed yield. Although increasing plant density resulted in decreased seed yield per plant, seed yield per unit area was similar at all densities.
Nasturtium flower and seed development studies showed that irrespective of density it takes about 12 days for the green floral bud stage to complete flowering and each flower needed 40-50 days from pollination to reach physiological seed maturity. Seed started shedding at 40 DAP at a moisture content of 78-80% and a maximum seed weight of 0.18 grams. Seed ripening occurs after 50 days from pollination after seed shedding on the ground surface. Maximum seed yield was achieved at 40 days after peak flowering at all densities.
The second stage of the study involved an assessment of the tolerance of nasturtium to various selective herbicides. This experiment was conducted in January-June 1992
in the glasshouse and was designed to provide information on the phytotoxicity of herbicides to nasturtium seedlings and plants. A wide range of soil and foliar applied herbicides were evaluated for their phytotoxicity to nasturtium. Four pre-emergence
chemicals, chlorpropham (3.2 kg ai/ha), alachlor (2 kg ai/ha), oryzalin (3 kg ai/ha) and trifluralin (0.8 kg ai/ha) were considered to be the most selective and are recommended for direct sown nasturtium crops. Post-emergence applications of asulam (1.6 kg ai/ha), haloxyfop (0.3 kg ai/ha), methabenzthiazuron (1.4 kg ai/ha) were also well tolerated by nasturtium seedlings.
Seed production possibilities for the production of garden nasturtium seed under New Zealand conditions are also discussed.