Biochemical and Molecular Knowledge about Developing Herbicide-Resistant Weeds

Herbicide resistance is the genetic capacity of a weed population to survive an herbicide treatment that, under normal use conditions, would effectively control the resistant weed population. Weeds have been evolving in conventional crop cultivars worldwide from selection pressure placed on them from repeated use of herbicides. In this chapter, we intend to explain the biochemical and molecular basis of herbicide resistance in weeds. On the other hand, herbicide resistance can be a useful tool so that weed scientists can use as important approach to control and manage weeds. There are several strategies for the production of HR crops by genetic engineering and the methods used in this process will be discussed in this chapter

The Effect of Organic Mulches and Metribuzin on Weed Control and Yield of Tomato (Lycopersicon esculentum Mill.)

To evaluate the effects of four kinds of organic non-living mulches (wheat straw, sawdust, coco peat and peat moss) and metribuzin (herbicide treatment) on weed control and yield of tomato cv. "CH" an experiment was designed in randomized complete blocks with 7 treatments and 3 replications at the College of Agriculture, Shiraz University in 2012. According to the results all mulch treatments showed lower efficiency in weed control than the metribuzin. Also, all mulch treatments showed higher weed density compared to metribuzin. When straw, among non-living organic mulches, showed lowest weed control (62.3 weed.m-2). According to the results the highest tomato yield per unit area was produced by using peat moss mulch (from 5.7 kg.m-2) and the lowest yield from weedy plots (1.2 kg/m-2). To calculate the percentage of predicted performance of each of the treatments, only Gompertz model was applied and only the beginning of weed interference between the treatments was taken into account

Absorption and Translocation of Dicamba in Dicamba-Tolerant Wild Tomato

Herbicide tolerance is commonly associated with reduced absorption and translocation of the herbicide; we hypothesized that the mechanism of dicamba tolerance in wild tomato (Solanum lycopersicum) accessions is due to these. The absorption and translocation of dicamba were investigated at a drift rate of 2.8 g ae ha-1, in three predetermined dicamba-tolerant wild accessions (TOM199, TOM198, and TOM300), and compared with two dicamba-susceptible (DS) commercial tomato cultivars [Money Maker (MM) and Better Boy (BB)]. Dicamba was quantified in three different parts of the tomato plant: two upper leaves, two lower leaves, and the roots, at 1, 3, and 7 days after treatment (DAT). Both MM and BB absorbed more dicamba then all the three DT accessions. The overall translocation pattern of dicamba was similar between DS cultivars and DT accessions, thus suggesting that tolerance to dicamba in wild accessions may not be associated with reduced translocation, but instead with reduced uptake of the herbicide. Additionally, reduced dicamba absorption in DT accessions may be attributed to their leaf characteristics, such as the presence of narrower leaves (3.42 leaf length/width ratio) and higher trichome density (20 no. mm-2) in DT accessions, than compared to DS cultivars (1.92 leaf length/width ratio, and 8 no. mm-2 trichome density).The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

The Response of Iranian Melon (<i>Cucumis melo</i> L.) Accessions to 2,4-D Drift

One of the most widely used auxinic herbicides in southern Iran’s cereal crop fields is 2,4-D; however, the concurrent growing season of off-season melons in this region potentially leads to herbicide drift from cereal fields to the melon fields. To study the response of some Iranian wild melon accessions to three simulated drift rates of 2,4-D, including 112.1, 11.2, and 3.7 g ae ha−1, a field experiment was conducted during 2019 and 2020 growing seasons. It was found that by increasing the herbicide rate from 3.7 to 112.1 g ae ha−1, the level of visual injury increased in all accessions. However, significant variation in herbicide tolerance was observed among different melon accessions. The MEL-R1 was the most tolerant accession with only 20% injury, while MEL-D8 displayed very high injury rate (ca. 90%) as assessed at 6 weeks after treatment during 2019. The accession MEL-S3 was the most tolerant to 2,4-D drift rates (20% injury) at 6 weeks after treatment during 2020. There was no significant difference between the accessions MEL-R1 and MEL-S3 in terms of their response to 2,4-D treatment during both years of the study, as these accessions fully recovered from injury over 6 weeks after herbicide treatment. In addition, only these two accessions were able to produce yield after the application of 2,4-D at the highest rate tested (112.1 g ae ha−1). Therefore, the melon accessions MEL-R1 and MEL-S3 could be recommended for cultivation and even for breeding programs in order to develop 2,4-D-tolerant commercial cultivars in regions where this herbicide is commonly used in cereal crop production adjacent to the melon fields

The Response of Iranian Melon (Cucumis melo L.) Accessions to 2,4-D Drift

One of the most widely used auxinic herbicides in southern Iran’s cereal crop fields is 2,4-D; however, the concurrent growing season of off-season melons in this region potentially leads to herbicide drift from cereal fields to the melon fields. To study the response of some Iranian wild melon accessions to three simulated drift rates of 2,4-D, including 112.1, 11.2, and 3.7 g ae ha−1, a field experiment was conducted during 2019 and 2020 growing seasons. It was found that by increasing the herbicide rate from 3.7 to 112.1 g ae ha−1, the level of visual injury increased in all accessions. However, significant variation in herbicide tolerance was observed among different melon accessions. The MEL-R1 was the most tolerant accession with only 20% injury, while MEL-D8 displayed very high injury rate (ca. 90%) as assessed at 6 weeks after treatment during 2019. The accession MEL-S3 was the most tolerant to 2,4-D drift rates (20% injury) at 6 weeks after treatment during 2020. There was no significant difference between the accessions MEL-R1 and MEL-S3 in terms of their response to 2,4-D treatment during both years of the study, as these accessions fully recovered from injury over 6 weeks after herbicide treatment. In addition, only these two accessions were able to produce yield after the application of 2,4-D at the highest rate tested (112.1 g ae ha−1). Therefore, the melon accessions MEL-R1 and MEL-S3 could be recommended for cultivation and even for breeding programs in order to develop 2,4-D-tolerant commercial cultivars in regions where this herbicide is commonly used in cereal crop production adjacent to the melon fields

Integrated Use of Herbicides and Mulching for Sustainable Control of Purple Nutsedge (<i>Cyperus rotundus</i>) in a Tomato Crop

Purple nutsedge (Cyperus rotundus L.) is a problematic weed in tomato (Lycopersicon esculentum L.) crops causing significant yield losses. Although several chemical options are available for this weed, the level of control is often unsatisfactory, and the consistent use of herbicides has a risk of resistance evolution. Therefore, we evaluated the efficacy of two herbicide options, halosulfuron and fomesafen + S-metolachlor, alone or integrated with natural and plastic mulches in controlling purple nutsedge in tomato crops in a three-year field study. The use of herbicides or mulches alone did not provide effective weed control (below 65%). However, the combination of natural mulch and fomesafen + S-metolachlor provided the most effective weed control by reducing the density and biomass of purple nutsedge by up to 83% and 81%, respectively, as compared with the season-long untreated control. The use of a natural mulch in combination with the herbicides halosulfuron or fomesafen + S-metolachlor also resulted in the highest tomato yield (ca. 3.3 kg per plant). This integrated treatment improved tomato yield by over 400% as compared with the season-long untreated control. The integrated use of a plastic mulch and two chemical options resulted in a 67–74% weed biomass reduction and a 332–368% yield increase over the season-long untreated control. These findings suggest that the combinations of herbicides and mulches are effective integrated weed management options for purple nutsedge in tomato crops

<b>The susceptibility of various watermelon (</b><b><i>Citrullus lanatus</i></b><b>) accessions to 2,4-D drift</b>

Due to the widespread application of 2,4-D in controlling the broadleaf weed species in southern cereal crop production systems of Iran, a risk of non-target drift threatens the watermelon crops in these regions. A 3-yr field experiment (2019-2021) was conducted to evaluate the susceptibility of sixteen Iranian watermelon accessions to the use of three 2,4-D drift doses. The WA-H712 was the least sensitive accession to 2,4-D doses of 3.7, 11.2, and 112.1 g ae ha-1 with the lowest herbicide injury of 15, 10, and 5%, respectively, when observed at 8 wk after treatment. Only the plants of accession WA-H712 tolerated the herbicide damage and produced economic yield after the application of 2,4-D at the drift dose of 112.1 g ae ha-1. The lower doses of 3.7 and 11.2 g ae ha-1 reduced the yield of this accession by only 10 and 20%, respectively, compared with untreated control. Therefore, based on these results, watermelon accession WA-H712 could be grown in areas prone to drift doses of 2,4-D. This accession can also serve as a genetic resource in conventional or modern breeding programs to introduce 2,4-D-tolerant cultivars of watermelon.</p