Abstract
ABSTRACT: A major problem affecting some upland rice cultivars is the increase in plant size when subjected to high doses of nitrogen fertilizer, leading to high levels of lodging. A method to reduce the height of upland rice, and therefore lodging, would be to use plant growth regulators. However, little information exists on the effect of these regulators on plant physiological processes. Therefore, the objective of this study was to evaluate the influence of trinexapac-ethyl application in upland rice via analysis of growth and gas exchange. The experiment was carried out under greenhouse conditions using the BRS Primavera cultivar. A completely randomized design with eight replications was used. Treatments were carried out with and without the application of the plant growth regulator, and plants were subject to two-stage assessments in which physiological and gas-exchange indices were measured. The use of trinexapac-ethyl improved the growth of rice plants from the flowering to the physiological maturity stage, resulting in higher values of leaf area ratio, specific leaf area, and leaf matter ratio in treated plants. At the same time, it provided smaller reduction in net CO2 assimilation at the physiological maturity stage. Thus, net/apparent assimilation rate did not change after the application of growth regulator, but relative growth rate decreased in these treated plants. These results indicate the occurrence of self-shading in rice plants induced by what might be a supra-optimum trinexapac-ethyl concentration.
Highlights
Rice (Oryza sativa L.) is one of the major cereal crops planted worldwide, and has great social and economic importance for the Brazilian population (NAVES; BASSINELLO, 2006; NASCENTE et al, 2011)
Plants without growth regulator treatment had higher relative growth rate (RGR) at the flowering stage; RGR values decreased at 125 DAE owing to physiological maturity and to leaf fall and death during senescence (Table 1)
In plants treated with trinexapac-ethyl, the RGR value was lower at the physiological maturity stage than at the flowering stage
Summary
Rice (Oryza sativa L.) is one of the major cereal crops planted worldwide, and has great social and economic importance for the Brazilian population (NAVES; BASSINELLO, 2006; NASCENTE et al, 2011). Upland rice crops occupy about 65% of the total cultivated area in Brazil. The lower yield of upland rice than of irrigated rice is mainly due to the uneven distribution of rainfall, which negatively affects the stages of plant growth in which water supply is crucial (GUIMARÃES et al, 2010). With the use of irrigation, rice plants are not subjected to water stress, and as a result, grain filling is not influenced by drought. The number of spikelets per panicle and the grain weight are greater than in upland rice (ARF et al, 2002; CRUSCIOL et al, 2006)
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