Competitive Ability of Rice Cultivars in the Era of Weed Resistance

Almost all plants are negatively affected by neighboring plants, which impose some degree of competition within the population, depending mainly on the quantity and quality of natural resources available in the environment. In rice cultivation, the occurrence of a high and diverse infestation of weeds results in high competition levels among the species. In addition, the high and growing number of cases about herbicide-resistant weeds, especially the widespread distribution of Imidazolinone-resistant weedy-rice and the high infestation of weeds belonging to the Echinochloa genus, has increased the competition levels within rice cultivation due to the lack of control. Therefore, the inclusion of rice cultivars with greater competitive ability represents a promising tool for weed management, since new cases of resistance to herbicides are often reported and alternative control strategies are scarce. The use of rice cultivars with a greater ability to suppress weeds can alleviate the competitive effect of these species, giving priority to the crop for the use of environmental resources due to the faster occupation of the ecological niches. Thus, this chapter aims to explore the competitive ability of rice cultivars against troublesome weed species, accounting for the role of their morphological and physiological traits as a function of environment-friendly crop practices

Rice Crop Rotation: A Solution for Weed Management

The challenges for weed management have increased in rice cultivation due to the high number of cases of herbicide-resistant weeds, especially the widespread distribution of imidazolinone-resistant weedy rice. Therefore, there has been particular interest in preventive, physical, and cultural methods in recent decades. In this context, the adoption of the rice-soybean rotation is reported to be one of the most important factors for weed management in rice fields. Additionally, the use of a diversified crop rotation enables the implementation of a broader herbicide program, which is an important feature influencing weed population dynamics. Rice-soybean rotation has been adopted by farmers to control problematic weed species, reduce seed bank of troublesome weed species, and prevent rice grain yield and quality losses caused by its interference. This crop rotation scheme has brought several benefits when it comes to weed management; however, there are also some drawbacks when adopting this strategy such as the limited productivity of soybean and new weed species becoming problematic, such as Conyza species. Thus, this chapter explores the advantages and disadvantages of adopting crop rotation in Brazilian lowlands, and proposes a set of strategies to successfully implement crop rotation in lowland soils as a tool for weed management

Weed Management in Sprinkler-Irrigated Rice: Experiences from Southern Brazil

Sprinkler rice saves water compared to paddy rice. However, in paddy fields, the water table is efficient for weed suppression. In sprinkler rice, there is no water table on soil; thus, weed management used in paddy rice may not be suitable for sprinkler rice, since herbicides and water table are expected to interact. Weed pressure in sprinkler rice is higher than in paddy rice; annual grasses are the main weeds in both paddy and sprinkler rice. Barnyardgrass, goosegrass, crabgrass and Alexandergrass show vigorous growth in sprinkler rice. A 3-year study shows that weeds in sprinkler rice reduce grain yield between 11 and 95%. Herbicides used in conventional and Clearfield® rice (clomazone, imazethapyr + imazapic, imazapyr + imazapic, pendimethalin and penoxsulam) were tested, contrasting paddy and sprinkler rice. Additionally, the technique locally called “needle-point” (glyphosate applied over the first-day emerging rice) was combined with pre- and postemergence herbicides. When using only pre- or postemergence, weeds reduced rice grain yield; a combination of products was the best option for sprinkler-irrigated rice. The Clearfield technology was efficient in controlling most weeds. However, using it combined to the needle-point promoted the best results. The main approaches for weed management in sprinkler-irrigated rice were summarized

EVALUATION AND GROUPING OF SUGARCANE GENOTYPES IN AGREEMENT WITH THEIR PHYSIOLOGIC CHARACTERISTICSOTYPES

AbstractThe objective of this work was to evaluate physiological characteristics of sugar cane genotypes, as well as characterize them in groups according to their similarity, checking the ability of ecological adaptability of these genotypes. The work was performed in field conditions, being assessed ten sugarcane genotypes (RB855113, RB835486, RB867515, SP80-1816, RB72454, RB925345, RB855156, RB937570, RB947520 and RB925211) in a randomized block design with three repetitions. It were evaluated the stomatal gas flow rate (U - μ mol s-1), the concentration of under-stomatal CO2 (Ci - μmol mol-1), the photosynthetic rate (A - μmol m-2 s-1), the CO2 consumed (Δ C - μmol mol-1), the stomatal conductance (Gs - mol m-1 s-1), the temperature gradient between leaf and air (Δ T), and the transpiration rate  (E - mol H2O m-2 s-1), being also calculated the water use efficiency (WUE - mol CO2 mol H2O-1) from the values of the amount of CO2 fixed by photosynthesis and amount of water transpirated. Both univariate and multivariate data analysis were made. The genotype SP80-1816 showed better water use efficiency, combined with low stomatal conductance and transpiratory rate. The cultivar RB855113 stood out by having high photosynthetic rate, and high consumption of CO2. The cultivar RB867515, in addition to showing high water use efficiency, also showed high photosynthetic rate. With respect to the multivariate analysis, the biotypes RB925345, RB925211, RB855156 and RB855113 are situated in different groups when compared to the others as to the physiological characteristics with respect to other genotypes with isolation in separate groups.Keywords: Saccharum spp. photosynthesis. Transpiration. Cultivars

Predictions for Weed Resistance to Herbicides in Brazil: A Botanical Approach

The intensive use of herbicides in agriculture has led to the appearance of resistant weed biotypes. Resistance is the inherited ability of a plant to survive following application of an herbicide dose which should be lethal. Morphophysiological weed traits help defining the risk to evolve resistance. These traits are not exclusive to the species but may be innate to botanical order, family, or genus. Four reference countries were screened about the nature of resistance—Australia, Canada, France, and the United States—and the data were used for predictions in the Brazilian scenario. Most weed species with resistant biotypes in the reference countries seem to be native to the continent. The most important botanical families with resistant biotypes in the reference countries were also among the first ones to develop resistance in these countries. There was a predominance of C3 species over C4 in the number of plant species with resistant biotypes in the reference countries. In Brazil, three orders are considered as high risk (Gentianales, Lamiales, and Solanales), besides the six already present. Furthermore, eight botanical families present superior risk to evolve resistance and for five of them (Caryophyllaceae, Polygonaceae, Rubiaceae, Convolvulaceae, and Solanaceae), resistance cases have not been reported to date in Brazil

Establishment of perennial forages intercropped with soybean for integrated crop-livestock systems

O objetivo deste trabalho foi avaliar a produção de grãos de soja (Glycine max) e o estabelecimento de forrageiras perenes, em cultivo consorciado. A soja foi avaliada em cultivo solteiro e consorciada com os capins: Megathyrsus maximus, cultivares Aruana e BRS Tamani; Urochloa brizantha, cultivares Xaraés, BRS Piatã e BRS Paiaguás; U. decumbens; e U. ruziziensis. Utilizou-se o delineamento experimental de blocos ao acaso, com sete repetições, nas safras de 2011/2012 e 2012/2013. No cultivo consorciado, as forrageiras foram semeadas 21 e 14 dias após a emergência da soja, na primeira e na segunda safra, respectivamente. O rendimento de grãos da soja solteira e o da consorciada não diferiram, exceto nos cultivos soja + U. ruziziensis e soja + 'BRS Paiaguás', que apresentaram menor rendimento no segundo ano de avaliação. O capim 'BRS Tamani' foi o mais adequado para estabelecimento em consórcio com a soja, ao se considerar suas características morfológicas e seu baixo potencial de competição. O consórcio de soja e forrageiras perenes contribui para supressão do crescimento de plantas daninhas e, de maneira geral, não compromete o rendimento da soja.The objective of this work was to evaluate soybean (Glycine max) grain yield and the establishment of perennial intercropped forages. Soybean was evaluated in sole crop and intercropped with the following forages: Megathyrsus maximus, Aruana and BRS Tamani cultivars; Urochloa brizantha, Xaraés, BRS Piatã, and BRS Paiaguás cultivars; U. decumbens; and U. ruziziensis. A randomized complete block design was used, with seven replicates, in the 2011/2012 and 2012/2013 crop seasons. In the intercropped system, the forages were sown 21 and 14 days after soybean emergence, in the first and second crop seasons, respectively. Grain yield did not differ for soybean in sole crop or intercropped, except for soybean + U. ruziziensis and soybean + 'BRS Paiaguás', which were less productive in the second year of evaluation. The 'BRS Tamani' forage was the most suited for intercropping with soybean, considering its morphological characteristics and its low competition potential. Soybean intercropped with perennial forages contributes to suppress weed growth and, overall, does not compromise soybean yield