Abstract
ABSTRACT In the agricultural environment, the occurrence of biotic and abiotic stresses, such as weed interference and soil water deficit is common. However, little is known about the effects of the interaction of these stresses on the growth of cultivated crops and weed species. Thus, the objective of this study was to evaluate the effects of competition and water deficiency on the growth of sunflowers and weeds. The experiment was performed in a randomized block design with four replications. The treatments were arranged in a 5 × 2 factorial design, with the first factor corresponding to the competition arrangements between the species (sunflower + Waltheria indica; sunflower + Amaranthus spinosus; and sunflower, W. indica, and A. spinosus in monoculture without competition) and the second factor corresponding to water regimes (irrigated and water deficit). The water deficit regime was established when the sunflower plants had six expanded leaves (V6 stage) and was maintained until the rate of CO2 assimilation of the plants reached values close to zero (6 days), after which irrigation was resumed and maintained until 40 days after emergence, when the plants were collected and evaluated. The growth components evaluated were plant height, leaf area, dry leaf mass, dry stem mass, dry root mass, and total dry mass. Competition between plants decreased sunflower, W. indica, and A. spinosus growth. W. indica and A. spinosus aggravated the negative effects of water deficiency on sunflower growth. The water deficit regime did not affect the growth of W. indica. A. spinosus was more competitive with the sunflower than was W. indica.
Highlights
The sunflower (Helianthus annuus L.) is one of the most important oleaginous species worldwide, being cultivated in all continents (CASTRO; LEITE, 2018)
The water deficit regime affected the growth rate of sunflower plants when cultivated alone and in competition with A. spinosus, which resulted in plants with lower heights (Figure 1A)
This could be caused by the stress related to water deficiency, which is characterized by a reduction in soil water content and, a reduction in leaf water potential, stomatal closure, loss of turgescence, and there is a decrease and/or interruption in cell growth (JALEEL et al, 2009)
Summary
The sunflower (Helianthus annuus L.) is one of the most important oleaginous species worldwide, being cultivated in all continents (CASTRO; LEITE, 2018). Among the factors contributing to this result are biotic and abiotic stresses, such as weed interference and soil water deficiency. The sunflower is a species that is considered tolerant to temporary soil water deficit (AHMAD et al, 2014); factors that increase the severity of droughts may reduce the ability of this species to tolerate stressful conditions. An increase in atmospheric temperature was found to intensify the negative effects of water deficiency on sorghum plants, a species recognized for its great adaptability to hot regions (LOBELL et al, 2015), and sunflower varieties that are susceptible to drought (KILLI et al, 2017)
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