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weed seed viability

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The percentage of abnormal seedlings did not differ from the control without herbicide, regardless of the phenological stage (Table 3). Abnormal seedlings are characterized by the incomplete structural formation of the seedling, resulting in plants with low vigor and lower competitive ability in cropping systems (Barth Neto et al. 2014). For weeds, the exploration of resources from the environment and field occupancy rely on seeds with high initial vigor and faster seedling emergence compared to the crop, important factors for growth and space occupancy (Vila-Aiub et al. 2015, Keshtkar et al. 2019).

Viable and non-viable dormant seeds did not differ for herbicides applied at pre-spike and anthesis compared to the control (Table 2). However, the increase of viable dormant seeds was found for the application of iodosulfuron-methyl, with values of 5% for the application at grain filling stage (Table 2). For non-viable dormant seeds there were no differences due to herbicide application, with greater values obtained for iodosulfuron-methyl application at grain filling (Table 2). Higher weed seed dormancy can cause longer longevity in the soil seed bank and allow population fluctuations due to slow dormancy release, especially under unfavorable environmental conditions (Neé et al. 2017). Furthermore, limited seed reserves reduce viability and increase the deterioration rate through microbiota predation, whereas environmental changes of temperature and soil moisture can affect gas exchange and reduce seed viability on the long-term (Vivian et al. 2008; Agostinetto et al. 2018).

Submission on Nov. 23, 2019 | First Publication on Jul. 15, 2020 | Open Access
Authors declared no conflict of interest
Article licensed under a Creative Commons Attribution-NonCommercial 4.0 International

Pre-harvest herbicide application reduces the Italian ryegrass seed viability

The adoption of chemical control and other management practices are strategies that can prevent the evolution of resistance and reduce its negative effects on crops, especially in fields with elevated number of resistant populations (Burgos et al. 2013). Efficient methods of weed control should increase seedling mortality, affect seed germination and plant development promoting the reduction of seed production and cause the exhaustion of the soil seed bank (Shaner and Beckie 2014, Chauhan et al. 2006). Thus, herbicides are considered important tools for integrated weed management due to the greater efficacy and lower costs compared to the physical and mechanical methods, reducing seed inputs and replenishment into the soil seed bank (Norsworthy et al. 2012). The inhibition of physiological processes caused by herbicides can affect seed formation, resulting in lower physiologic quality (Campos et al. 2012). For example, paraquat and glyphosate application before the complete wheat seed formation can cause lower germination and reduce the vigor (Perboni et al. 2018). In contrast, non-viable seeds production in Italian ryegrass after herbicide application depends on the plant phenological stages to provide higher effects on physiological quality.

Figure 1. Seed production and 1000 seed weight after paraquat, ammonium-glufosinate, iodosulfuron-methyl and clethodim application for seed inviabilization of Italian ryegrass in different phenological stages. Same lowercase letters compare the herbicide effects in the different stages, and uppercase letters compare the herbicides in each stage by Duncan´s test (p<0.05). * significant effect for control without herbicide by Scheffé test (p<0.05).

MATERIAL AND METHODS

For the seed viability, the analyzes were carried out in a seed laboratory using the completely randomized experimental design with four repetitions. A sampling from each treatment was performed, and 50 seeds were placed in each transparent boxes (11.5×11.5×3.5 cm), containing two sheets blotter paper, previously moistened with distilled water in an amount to 2.5-fold the paper weight. The boxes were put in a chamber of Biochemical Oxygen Demand (BOD) for 14 days at alternating temperature 20/30 o C in dark/light, and 8 h of photoperiod, according to the Brazilian Rules for Seed Testing (Brasil 2009). Seed viability was evaluated at 14 days after starts the germination testing, based on the germination percentage, abnormal seedlings, dead seeds, percentage of dormant viable and non-viable seeds. The non-germinated seeds were analyzed in a 1% tetrazolium solution after longitudinally cut of embryo and imbibition at 30 o C of temperature for 6 h, with check-in in a stereo microscope (Brasil 2009).