Environmental effects on seed development and hardseededness in Stylosanthes hamata cv. Verano. II. Moisture supply and illuminance

Abstract

The effects of variation in moisture supply and of level of illuminance during seed formation on the development of hardseededness and on the seed production of Stylosanthes hamata cv. Verano were studied in two glasshouse experiments. Verano plants were grown in pots containing 1.6 kg soil and were watered daily to field capacity until early flowering (43 days after seedling emergence). From day 43 to day 116, the plants were watered every 1, 2, 3 or 4 days. Leaf water potential immediately before rewatering varied from c. -20 to -28 bars in the 4-day treatment. Yields of seed pods were 5.8, 4.6, 3.8 and 3.8 g in the I-, 2-, 3- and 4-day treatments respectively. Severe water stress greatly reduced inflorescence density, had lesser negative effects on frequency of blooming, floret number, seed setting and proportion of florets forming a lower (beakless) articulation, and increased individual pod weight. Watering treatment had transitory and inconsistent effects on hardseededness. Seed production of Verano plants grown after flowering under shades with 30,40 or 59 % transmission or no shade was reduced by low level of illuminance, mainly because of effects on floret number per inflorescence; the proportion of florets forming a lower articulation and individual pod weight (but not seed setting) was also reduced by shading. The seed moisture content at different harvest occasions appeared to influence hardseededness, but shading had no consistent effect.