Crescimento e partição de assimilados em cultivares de arroz diferindo no potencial de produtividade de grãos

Abstract

RESUMOForam estudados o crescimento, a partição de assimilados e a produção de grãos nas cultivares de arroz BRS Pelota (maior produtividade) e BRS Firmeza (menor produtividade). O experimento foi realizado em casa de vegetação, com plantas cultivadas em vaso. Utilizou-se o delineamento experimental inteiramente casualizado, com duas cultivares, nove coletas e quatro repetições por tratamento. Com a cultivar BRS Pelota houve maior acúmulo de matéria seca total (W t ), principalmente no fim do ciclo, bem como maior área foliar (A f ). A matéria seca alocada para o colmo + bainha e às panículas também foi maior em BRS Pelota. Porém, a porcentagem de W t destinada às panículas aos 125 DAE foi semelhante entre as cultivares. Em BRS Firmeza, o aumento em W t nas raízes pode ter influenciado o direcionamento de fotoassimilados para os grãos e contribuído para o atraso na senescência das plantas. A produtividade de BRS Pelota foi maior que a de BRS Firmeza (17,4 contra 11,8 g por vaso) e seu número de panículas por planta por vaso foi três vezes superior em relação à cultivar BRS Firmeza. O componente de produção de maior expressão no rendimento foi o número de panículas. A maior produtividade da cultivar BRS Pelota pode estar relacionada à maior área foliar e sua duração, o que permite o fornecimento de elevada quantidade de fotoassimilados por um período maior.Palavras-chave: matéria seca, análise de crescimento, área foliar, BRS Firmeza, BRS Pelota. ABSTRACT GROWTH AND ASSIMILATES PARTITIONING IN RICE CULTIVARS DIFERING IN GRAIN YIELD POTENTIALThe growth, assimilate partitioning and grain yield in BRS Pelota (high yield) and BRS Firmeza (low yield) rice cultivars were evaluated. The experiment was conducted in greenhouse (Department of Botany, Federal University of Pelotas) with complete randomized design composed by two cultivars, nine plant sampling times and four replicates. BRS Pelota rice cultivar exhibited higher accumulation of total dry matter (W t ), mainly at the end of life cicle, as well as higher leaf area (A f ). The dry matter allocated toward culm + sheath and panicles was higher in BRS Pelota. However, the W t percentage accumulated in panicles at 125 DAE was the same between cultivars. In BRS Firmeza the increase in W t in the roots may had influenced photoassimilates partitioning toward grains, and also contributed to delay of in plant senescence. Grain yield was higher in BRS Pelota than in BRS Firmeza (17.4 versus 11.8 g vaso), and also panicle number was three times greater in relation to BRS Firmeza. The yield component which exhibited higher relevance for productivity was the panicle number. The higher grain yield of BRS Pelota could be related to higher leaf area and leaf area duration, which allows the provision of elevated quantity of photoassimilates during longer period time.

Trinexapac-Ethyl Affects Growth and Gas Exchange of Upland Rice

“…In plants treated with trinexapac-ethyl, the RGR value was also lower at the physiological maturity stage than at the flowering stage. This downward trend in the relative growth rate as a function of the plant's age is in accordance with the observations of Stone, Portes and Moreira (1988), and Falqueto et al (2009) in rice plants. According to Taiz and Zeiger (2009), RGR reflects the increase in plant dry matter of any organ over a period of time and is a function of the initial size, i.e., of the preexisting material.…”

“…In addition, increased respiratory activity during plant development and self-shadowing can also decrease RGR (URCHEI; RODRIGUES; STONE, 2000), as observed in this experiment. At the end of the plant cycle, RGR is negative due to the death of leaves and buds and to the gradual production of nonassimilatory tissues (MILTHORPE; MOORBY, 1974;FALQUETO et al, 2009), as observed in this trial both with and without growth regulator application (Table 1). Alvarez, Crusciol and Nascente (2012), working with BRS Primavera under field conditions, also observed a steady reduction in RGR with increase in DAE.…”

“…This indicates that, at the concentration used, trinexapac-ethyl-treated plants produced greater leaf area than non-treated plants. Results observed by Aguiar Neto et al (2000) in potato, by Silva et al (2005) in sugarcane, and by Falqueto et al (2009) in rice show that similar reductions in SLA are due to the translocation of reserves from leaves to other parts of the plant, such as stalks. Table 1.…”

“…Likewise, lower LAR values were observed, regardless of the treatment, at physiological maturity stage than at the flowering stage (Table 1). After flowering, LAR values were lower mainly due to the presence of non-assimilatory tissues and structures, in addition to self-shadowing, senescence, and leaf fall (URCHEI; RODRIGUES; STONE, 2000;FALQUETO et al, 2009). At the physiological maturity stage, higher LAR values were observed in treatments with growth regulator application than in treatment without growth regulator.…”

“…The technique also assesses photosynthetic production by means of dry matter accumulation, allowing a better understanding of the factors that affect grain yield (URCHEI; RODRIGUES; STONE, 2000;FALQUETO et al, 2009;NASCENTE, 2012a;OLIVEIRA et al, 2013). Furthermore, grain yield in rice and other cereals is related to the amount of CO 2 fixed by the plant and to the partitioning of the photosynthesized substrate for the growth of grains and of other plant organs (TAIZ;ZEIGER, 2009;CONCENÇO et al, 2011;FAGERIA;MORAES;VASCONCELOS, 2011).Thus, the objective of this study was to assess the influence of the application of trinexapac-ethyl on upland rice crops through the analysis of plant growth and gas exchange.…”