Abstract

In order to study the critical growth stages and the most tolerant rice varieties in both lowland and upland rainfed ecosystems, an experiment arranged in split plots based on randomized complete block design was conducted under field conditions with 3 replications. Three stress timing irrigation treatments (no stress, vegetative moisture stress, and reproductive moisture stress) were assigned as th main plots, while 6 varieties (NERICA1, NERICA2, NERICA4, TXD 306, Tai and Komboka) were assigned as sub plots. Moisture stress during reproductive phase caused the highest reduction in grain yields (between 58 - 79%) followed by stress induction during vegetative phase, with 26 - 46% yield reduction; while no stress control moisture regime caused 0% reduction, that is did not cause any reduction. All NERICA tested varieties were the most tolerant to moisture stress during vegetative; they had only 26 - 36% grain yield reduction, compared to the lowland rice varieties which had 38 - 46% reduction during the same stress period. NERICA2 was the most tolerant variety to moisture stress during reproductive phase under the upland condition (66% reduction) followed by NERICA1 (67% reduction), while NERICA4 was the last (76% reduction). Tai was the most tolerant variety under lowland condition (58% reduction) followed by TXD306 (67% reduction), while Komboka was the last in lowland varieties with 79% reduction. Moistures stress during vegetative and reproductive growth phases significantly reduced plant height, shoot dry weight, number of tillers, number of panicles, spikelets, fertile grain, 1000 grain weight and harvest index in all the varieties.  It was concluded that the most critical growth stage among the tested varieties is the reproductive growth phase. Stress induction at reproductive caused more reduction of 32% - 33% in grain yield compared to stress induction during vegetative growth phases. NERICA2 and Tai are the most tolerant varieties to moisture stress during the reproductive phase and therefore are recommended in areas with rainfall scarcity.

Key words: Yield reduction, moisture stress, NERICA rice, tolerant varieties.

Abbreviation

MAFC, Ministry of Agriculture Food security and Cooperatives; GRiSP, Global Rice Science Partnership; URT, United Republic of Tanzania; IRRI, International Rice Research Institute.