Weed Vegetation Structure in an Area of Organic Acerola Cultivation, Parnaíba, Piauí, Brazil

ABSTRACT: This study aimed to identify and quantify the weed species in an area of organic acerola cultivation in the Distrito de Irrigação dos Tabuleiros Litorâneos do Piauí (DITALPI) in Parnaíba, Piauí, Brazil. Phytosociological sampling was completed in the rainy season, before the farmers adopted management techniques for the plants. Thirty plots of 0.25 m2 were sampled. The plots were located between crop rows, which consisted of herbaceous-subshrub plants. The absolute and relative covers and the absolute and relative frequencies of each species were calculated based on the occurrence and cover of each species. In total, 25 species comprising 13 families were registered, among which the Poaceae family that presented the largest number of species. Commelina benghalensis occurred the most frequently overall. Shannon’s diversity index (H’) and evenness were calculated as 2.30 nats ind-1 and 0.69, respectively. Five species accounted for 79.33% of absolute cover at DITALPI. The species were distributed heterogeneously within the field, and Commelina benghalensis, Urochloa plantaginea, Panicum maximum, Amaranthus spinosus, Cynodonsp., and Cyperus aggregatus were the species most likely to infest the acerola crop. As DITALPI is an area of organic cultivation, understanding these species is essential to help farmers select the best form of control.

Weeds Associated with Banana Crops in Magdalena Department, Colombia

ABSTRACT: This study was conducted to determine the richness and composition of weed communities associated with banana plantations in Magdalena department, Colombia. Between September 2016 and May 2017, a total of 164 hectares were assessed over four agroecological zones (Alta, Media, Baja and Norte); in each zone, three representative farms were selected where, through zigzag paths, botanical collections were made in cultivated lots. Information on life cycle, growth habit and origin of each species was included. The floristic composition was represented by 204 species distributed among 143 genera and 54 families. Poaceae, with 31 species, was the family with the highest species richness, followed by Fabaceae (12) and Asteraceae (11). From the total species recorded, 113 are perennial (55%) and 91 are annual (45%); 141 species are herbaceous (68%), 38 are climbers (20%), and 25 are arboreal or shrubby (12%). Native species predominate over introduced species. The species richness does not differ significantly between the sampling zones, but the weed community composition does. The presence of common species reported as important weeds worldwide was recorded in the four zones. However, some species were recorded in only one of the zones, generating a differential composition pattern. Comparison with local inventories showed changes in the composition of the weed complex over time. The presence of various species not previously considered weeds in the banana crops of this region is highlighted.

Modeling the Emergence and Growth of Alligatorweed at Different Field Capacity Levels

ABSTRACT: A study focusing on different field capacity levels was planned in the Weed Science Lab, Department of Agronomy, University of Agriculture Faisalabad. Fresh alligatorweed was harvested from the Agronomy fields and cuttings (2 cm length) were made from it. These cuttings were placed at 25%, 50%, 75% and 100% field capacity levels in pots for 25 days. The results of the experiments revealed that at all field capacity levels, fragments of alligatorweed were able to sprout and grow. Increased moisture levels significantly increased the emergence ability and survival of the alligatorweed plants upto a certain level. Compared with the control (25% FC), emergence time of the sprouts in the maximum moisture regime (100% of FC) decreased by 40% (12.94 days vs.7.17 days). By contrast, the survival rate of the fragments decreased by 60% (5 vs. 1.75) although survival and growth rate increased at first with 50% FC and 75% FC. Maximum sprouting and growth were found at 50% field capacity. Field capacity does affect the sprouting capacity of alligatorweed fragments but it has only a little influence on growth parameters. The results suggest that alligatorweed can sustain dry conditions to a great extent and also has the ability to sprout and grow in fully submerged soils.

Genetic Dissimilarity in Conyza sumatrensis Revealed by Simple Sequence Repeat (SSR) Markers

ABSTRACT: In view of the rapid evolution of Conyza sumatrensis populations resistant to glyphosate, it is necessary to understand the genetic diversity aimed to improve strategies for managing this weed. We investigated the genetic dissimilarity among 15 biotypes of C. sumatrensis from different geographic regions using microsatellite loci. The biotypes, were cultivated in a greenhouse to obtain vegetal material for DNA extraction. Nineteen microsatellite markers (SSR), were developed for C. sumatrensis biotypes. The genetic dissimilarity was estimated by the Jaccard coefficient (JC) and the biotypes grouped by the UPGMA method. The results demonstrated a high dissimilarity (JC = 7.14 to 82.62) of the analyzed material, with the biotypes forming five groups, being one group formed just by the susceptible biotype and in the others grouped by biotypes from distinct locations in the same group The high genetic diversity of C. sumatrensis indicates that the biotypes may show different responses to different management strategies, and that the mechanisms of resistance to herbicides and characteristics of evolution of populations due to adaptability may be some of the factors involved in the genetic variability of the species.