Perspectives for using light quality knowledge as an advanced ecophysiological weed management tool

Abstract

-The current knowledge of light quality effects on plant morphogenesis and development represents a new era of understanding on how plant communities perceive and adjust to available resources. The most important consequences of light quality cues, often mediated by decreasing in red far-red ratios with respect to the spectral composition of incident sunlight radiation, affecting weed-crop interaction are the increased plant height and shoot to root ratio in anticipation of competition by light quantity, water or nutrients. Although the concepts related to light quality have been extensively studied and several basic process of this phenomenon are well known, little applications of photomorphogenic signaling currently are related to agricultural problems or weed management. The objectives of this review are to describe how light quality change can be a triggering factor of interspecific interference responses, to analyze how this phenomenon can be used to predict weed interference, to reevaluate the critical periods of interference concept, and to discuss its potential contribution towards developing more weed competitive crop varieties. Knowledge on light quality responses involved in plant sensing of interspecific competition could be used to identify red/far-red threshold values, indicating when weed control should be started. Light quality alterations by weeds can affect grain crop development mainly in high yielding fields. Unlike the traditional concept or the critical period of competition, light quality mediated interference implies that the critical period for weed control could start before the effects of direct resource (water, nutrients and available light) limitation actually occur. The variability in light quality responses among crop genotypes and the identification of mutants insensitive to light quality effects indicate that this characteristic can be selected or modified to develop cultivars with enhanced interspecific interference ability. Knowledge on light quality-elicited responses represents a new possibility to understand the underlying biology of interspecific interference, and could be used in the development of new weed management technologies.Keywords: critical period for weed control, crop-weed interactions, red/far-red ratio, shade-avoidance, weed thresholds.RESUMO -O atual conhecimento sobre os efeitos da qualidade da luz representa uma nova era da compreensão dos processos envolvidos na percepção e ajuste das plantas em função dos recursos disponíveis no ambiente. As consequências mais importantes da diminuição da qualidade de luz, que se relaciona principalmente com a diminuição da relação vermelho/ vermelho-extremo, que ocorrem nas interações entre culturas e plantas daninhas são o aumento da estatura e da relação parte aérea/raiz. Essas alterações são tentativas de antecipar os efeitos da concorrência futura por quantidade de luz, água ou nutrientes. Embora vários conhecimentos básicos relacionados com a qualidade da luz tenham sido desenvolvidos há muito tempo, poucas...

Competitive Ability of Lettuce with Ryegrass1

“…According to Ballaré & Casal (2000), the effects of the light signals perceived by photoreceptors may be different for the culture and the weeds when in competition. This fact may be explained by the fact that the plant invests energy for the growth of the aerial part and the radicular system, showing, consequently, a considerable reduction on its growth and development, and one of the main morphological changes observed is the stem etiolation (Merotto Jr. et al, 2009). According to the authors, this symptom may be explained as a scape mechanism and a search for luminous radiation of good quality and sufficient quantity to reestablish the energetic balance of the plant.…”

Weed Management in the Soybean Crop

“…The initial growth rate is directly related to light interception and use in earlier stages of the plant cycle, allowing a greater leaf area development which provides to crop a higher competitive ability [32,44].…”

Physiology of Crops and Weeds Under Biotic and Abiotic Stresses

“…Interspecific and intraspecific plant competition affect the amount and the quality of the final product, as well as its efficiency in utilization of environmental resources (VanderZee & Kennedy, 1983;Melo et al, 2006). This is noted when assessing physiological characteristics associated to photosynthesis, such as concentration of internal and external gases (Kirschbaum & Pearcy, 1988), light composition and intensity (Merotto Jr. et al, 2009) and mass accumulation by plants under different conditions. Although gas exchange capability by stomata is considered a main limitation for photosynthetic CO 2 assimilation (Hutmacher & Krieg, 1983), it is unlikely that gas exchange will limit the photosynthesis rate when interacting with other factors.…”

“…When plants do not receive these wave lengths in a satisfactory manner, they need to adapt themselves in order to survive (Attridge, 1990). When under competition for light, the red and far-red ratio affected by shading is also important (Merotto Jr. et al, 2009) and influences photosynthetic efficiency (Da Matta et al, 2001). The physiological parameters associated to photosynthesis rate and dynamics of water use in plant species will be presented, and on the following the application of these parameters in studies of plant competition (both in crops and weed species), and studies of herbicide toxicity to crops and forest trees will be discussed.…”

“…Studies conducted by some researchers showed that responses to changes in Red:Far Red (R:Fr) ratios occur before the mutual shading among neighbors. Based on these studies, it was proposed that the Far Red radiation, which is reflected by adjacent leaves, is a means of early detection that signals the imminence of competition during canopy development (Ballaré et al, 1990;Merotto Jr. et al, 2009;Aspiazú et al, 2010b). In addition, some species are capable of recognizing others by the amount of radiation reflected in each wave lengthessentially, the composition of the light reflected (Larcher, 2004;Aspiazú et al, 2010b Table 3.…”