Responses of Growth and Yield of Rice Varieties to Contrasting Hydrothermal Regimes during Vegetative and Reproductive Growth Phases in Akure, a Rainforest Zone of Nigeria

Experiments were conducted in the screenhouse to determine the effects of watering and temperature regimes on the growth, seed yield and yield components of rice. The experiment was a split-plot scheme involving 4 x 3 x 2 factorial combinations of rice varieties (Igbemo, Millina, Cherie and Nerica 7), watering regimes, ambient and high temperature conditions arranged in Completely Randomized Design with four replications. Watering regimes (40, 70 and 100% field capacity (FC) consisted of water application at 1.5, 1.0, 0.6 litres of water per pot at 4 days interval) were imposed two weeks after germination. At the onset of flowering, a set of experimental materials grown under the watering regimes were retained under ambient temperature (29-32°C) and atmospheric dryness (vapour pressure deficit: 2.3 – 2.8 kPa: moderate humidity) and another set were grown under conditions of high temperatures (35-42°C) and VPD (3.2 - 3.8 kPa: low humidity). Data were collected on root and shoot weights, number of green and dead leaves, tillers/stand, spikelets/panicle, seed and panicle weights. The tested rice varieties differed in growth and yield characters. In general, the landraces (Igbemo and Benue types) produced a higher number of tillers and filled grains and heavier seeds/panicle. The 100 and 70% FC watering enhanced rice performance: height, leaf area, number of tillers and panicle and seed yield, 100 seeds weight compared to the 40% FC soil moisture conditions. However, compared with growth under field capacity moisture, rice had declined growth and yield characters under 70 and 40% FC. The chlorophyll and soluble carbohydrate contents in leaf and stem which differed among the varieties were also affected by watering regimes and growing environment conditions. The responses of rice varieties varied under conditions of high temperature and low humidity during the reproductive phase in combination with variable root zone moisture. Under low humidity and high temperature conditions during reproductive phase: Compared with the landraces, Nerica 7 was best for leaf area and 100 seed weight and lowest unfilled grains/panicle. High air temperatures and low humidity during reproductive phase enhanced leaf senescence and sterility of spikelets and seeds (empty seeds). The strong interplay between soil moisture deficit and temperature stress especially during the reproductive phase depressed rice growth and yield. High temperature and low humidity appeared to have accentuated soil moisture deficit constraints on the growth and yield of rice.