credit seminar herbicide resistance in wheat crop

Herbicide resistance is a growing global issue that poses a serious challenge to agriculture and the environment. Herbicides have long been a staple in modern farming for controlling weeds, ensuring crop yields, and reducing labor. However, the widespread and often repeated use of these chemicals has led to the development of herbicide-resistant weeds, threatening agricultural sustainability and food security. This essay will explore the mechanisms of herbicide resistance, its impact on agriculture, strategies to manage resistance, and the implications for future agricultural practices.

### 1. Introduction

Herbicide resistance refers to the ability of a weed species to survive and reproduce despite exposure to herbicides that would normally kill them. The development of herbicide resistance has been a major concern for farmers and agricultural scientists since it leads to a reduction in the effectiveness of herbicides, thus limiting the ability to control weed populations. This phenomenon is not only a technical problem but also an economic and ecological one, as it necessitates the use of more expensive, environmentally harmful, or less effective methods of weed control.

### 2. Causes of Herbicide Resistance

The primary cause of herbicide resistance is the selection pressure exerted by repeated herbicide application. Over time, natural genetic variation within weed populations allows some individuals to survive herbicide treatment. These survivors reproduce, passing on their resistance traits to subsequent generations, and thus, resistance becomes more widespread in the population. There are several key factors that contribute to the development of herbicide resistance:

#### 2.1 Genetic Mutation
The most straightforward mechanism of herbicide resistance is genetic mutation. A single mutation in a weed’s DNA can confer resistance to a particular herbicide, allowing the plant to survive despite being exposed to a lethal dose. This mutation can alter the target site of the herbicide, rendering the herbicide ineffective. For example, mutations in the acetolactate synthase (ALS) enzyme or the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene can confer resistance to herbicides like sulfonylureas or glyphosate, respectively.

#### 2.2 Cross-Resistance and Multiple Resistance
Some weeds can develop cross-resistance to herbicides with different modes of action. This occurs when a mutation allows a weed to survive not just one herbicide but several. Additionally, multiple resistance arises when a weed develops resistance to more than one herbicide, each targeting a different enzyme or pathway. For example, a weed may develop resistance to both glyphosate (which inhibits EPSPS) and acetochlor (which inhibits ALS), making it resistant to two different herbicide classes.

2.3 Evolutionary Pressures
Weeds with a high reproductive rate and the ability to adapt quickly to environmental pressures are more likely to develop resistance.

1. CREDIT SEMINAR ON HERBICIDE RESISTANCE AND ITS MANAGEMENT IN WHEAT PRESENTED BY : MANEESHA MSc. 1 st year (2 nd sem.) 19-M-FP-01

2. INTRODUCTION HOW DOES RESISTANCE EVOLVE MULTIPLE RESISTANCE IN P. minor EFFECT OF CLIMATE CHANGE ON WEEDS MANAGEMENT RESEARCH FINDINGS CONCLUSION NEED OF AN HOUR

3. What a farmer need from his crop ????? T ension-free cultivation Green fields Bountiful harvest

4. Rice-wheat Punia et al., 2017 Phalaris minor Chenopodium album Rumex dentatus Weeds of wheat

5. Change in weed flora over time : In 1960’s Carthamus oxycantha – major weed of wheat. eliminated increase in irrigated area . Early 1960’s – high yielding dwarf varieties need higher doses of fertilizers, assured irrigation result replacement of broad leaf weeds by P. minor and A vena ludoviciana . ( M alik and S ingh, 1995; B alyan and Malik,2000; Yadav and Malik,2005)

6. Herbicide resistance Inherited ability of a plant to survive and reproduce following exposure to dose of herbicide normally lethal to wild type. After a time

7. Herbicide resistance : background There are currently  512 unique cases  (species x site of action) of herbicide resistant weeds globally, with  262 species  (152 dicots and 110 monocots). Weeds have evolved resistance to  23 of the 26 known herbicide sites of action and to 167 different herbicides . Herbicide resistant weeds have been reported in  92 crops in 70 countries . Source : Heap, I.  The International Herbicide-Resistant Weed Database . Online. Tuesday, June 9, 2020. Available www.weedscience.org

8. 1 st herbicide resistant weed : S enecio vulgaris resistant to triazine in USA. (Ryan,1970) In india , Sr. No. weed Site of action 1. Phalaris minor Multiple Resistance: 3 Sites of Action  ACCase inhibitors (A/1) ALS inhibitors (B/2) PSII inhibitor ( Ureas and amides) (C2/7) 2. Rumex dentatus ALS inhibitors (B/2) Source :   Heap, I.  The International Survey of Herbicide Resistant Weeds.

9. Type of resistance 1. Single herbicide resistance 2. Cross herbicide resistance Herbicide A MOA #1 Herbicide A MOA#1 Herbicide B MOA#1

10. 3. Multiple Herbicide resistance MOA#1 Herbicide A Herbicide C MOA#2

11. Evolution of Isoproturon resistance in P. minor By 1993, resistance affected area between 0.8-1.0 Mha in N-W india mostly in Punjab(0.3Mha) and Haryana(0.55Mha) ( Walia et al.,1997).

12. Multiple resistance in P.minor Multiple herbicide resistance in P. minor across three modes of action: Photosynthesis at the PSII site, Acetyl-coA carboxylase ( ACCase ), Acetolactate synthase (ALS) inhibitors (Heap,2016)

13. Mode of action : 1. PS II inhibitors : P680 PQA or Q PQB P680 PQA or Q PQB Phenylureas , triazines , uracils etc. (D1 protein) Pheo e -

14. 2. Acetyl co-A inhibitors : ACCase inhibitors are group A herbicides to which resistance in weeds can evolve in less than 10 applications of this herbicide group ( Beckie , 2006) includes aryloxyphenoxypropionate (FOPs) cyclohexanedione (DIMs) phenylpyrazolin (DENs)

15. 3. Acetolactate synthase (ALS) or Acetohydroxy acid synthase (AHAS) Inhibitors : Include sulfonylureas, imidazolinones , triazolopyrimidine sulfonanilides , pyrimidinylthiobenzoates .

16. Mechanism of resistance development in P. minor : P. Minor show resistance to isoproturon through enhanced degradation. The degradation takes place via N- dealkylation , and ring alkyl oxidation. Increased herbicide metabolism due to NADPH-cytochrome P-450 monoxygenase is responsible for resistance to inhibitors of ACCase , ALS, PS II in a no. of grass weed species including Phalaris minor in india . (Kirkwood et al., 1995; Singh et al.,1998)

17. Level of resistance in P. minor to different herbicides in India Herbicide Resistance factor Reference Isoproturon 2.0-15.0 Malik et al., 1995; Rasool, 2016 Clodinafop 1.2-4.0 Yadav et al., 2002; Dhawan et al., 2009; Rasool , 2016 Sulfosulfuron 1.2-10.0 Yadav et al.,2002; Dhawan et al., 2005; Dhawan et al.,2009 Tralkoxydim 1.2-1.7 Yadav et al., 2002 Fenoxaprop 3.7-10.0 Dhawan et al.,2005; Dhawan et al., 2009; Rasool, 2016 Bhullar et al ., 2017

18. Metsulfuron resistance in Rumex dentatus M ajor broadleaf weed of wheat. I n India shows resistance to ALS inhibitors in 2014. It has shown cross resistance to mesosulfuron + iodosulfuron , pyroxsulam , halauxifen + florasulam . For its control, carfentrazone , 2,4-D amine, Pendimethalin and isoproturon were found effective. Source : Heap, I. The International Survey of Herbicide Resiatant Weeds . Online. Tuesday, June 9, 2020. Available. www.weedscience.org

19. Effect of climate change on weeds in wheat A ffect weeds as well as crop yields directly or indirectly. Study conducted by IARI indicates the possibility of loss of 4-5 Mt in wheat production with every rise of 1˚C throughout growing season. (Aggarwal,2008). C3 photosynthetic pathways expected to benefit more than C4 from CO2 enrichment.

20. In wheat (C3), majority weeds are C3. In this case weed growth is favoured . Perennial weed growth is also increases with increase in CO2. Climate change reduce the effectiveness of current weed management practices. (Ziska et.al, 1999; Ziska and Teasdale,2000 ) Problem of herbicide resistant weeds and poor weed control with herbicide application may increase with climate change .

21. Management of herbicide resistant population : Cultural / ecological approaches : Competitive and high yielding variety Certified crop seeds Stale seedbed technique Closer row spacing Proper time, method and rate of sowing Crop rotation Crop residue management

22. Mechanical and manual approaches : Tillage practices Harrowing Soil solarization Manual wedding Soil solarization

23. Herbicide Chemical class Mode of action Dose (g/ha) Year of recommendation Time of application Pendimethalin Dinitroaniline Microtubule formation inhibitor 750 1982-83 PRE Trifluralin Dinitroaniline Microtubule formation inhibitor 1200 2003-04 PRE Clodinafop propargyl aryloxyphenoxypropionate ACCase inhibitor 60 1998-99 POST Fenoxaprop aryloxyphenoxypropionate ACCase inhibitor 100 1998-99 POST Sulfosulfuron sulfonylurea ALS inhibitor 25 1998-99 POST Mesosulfuron + iodosulfuron Sulfonylurea ALS inhibitor 14.4 2005-06 POST Pinoxaden phenylpyrazole ACCase inhibitor 50 2008-09 POST Metribuzin + fenoxaprop Triazinone + aryloxyphenoxypropionate PS II inhibitor + ACCase inhibitor 275 2012-13 POST HERBICIDE MANAGEMENT : Alternate herbicides Bhullar et al .,2017

24. Herbicide rotation Herbicide mixture Integrated weed management (IWM)

25. RESEARCHFINDING

26. 26 Population Mortality % of P. minor S 25g/ha SM 32g/ha M MI Ambala – Jansui Head 15 40 45 60 Ambala – Adumajra 35 30 30 60 Jind – Majra 20 40 45 55 Hisar – Nangla 20 70 25 60 Karnal – Uchana 15 5 40 40 Karnal – Sagga 15 15 25 10 Fatehbad – Badi Birthal 15 45 5 75 Jind – Raseedan 25 15 45 75 Kurukshetra – Chanarthal 25 50 15 75 Jind – Pipaltha 30 50 75 75 Kurukshetra – Munak 25 35 20 75 Rohtak 45 25 60 75 Hisar, HAU – Farm 25 25 30 75 Hisar-Bass 45 20 15 75 Kaithal – Gumthala 15 5 20 75 Hisar – Lalodha 25 20 20 75 Hisar – Vaibhalpur 35 20 20 75 Sirsa, University Farm 30 50 5 75 LSD (P=0.05) 6.9 7.1 10.3 20.5 S - Sulfosulfuron (25 g/ha); SM - Sulfosulfuron + metsulfuron (32 g/ha ); M - Mesosulfuron + iodosulfuron (14.4 g/ha); MI -Mesosulfuron + iodosulfuron (28.8 g/ha) TABLE 4. Dhawan et al ., 2012 Table 1 :Effect of sulfosulfuron, sulfosulfuron + metsulfuron and mesosulfuron + iodosulfuron on mortality in different Phalaris minor populations

27. 27 Table 2 :Per cent control of weeds at 75 DAS and weed population at harvest as influenced by different herbicidal treatments in wheat Punia et al., 2017

28. 28 Weed dry weight (g/ m 2 ) Treatments P. minor Rumex dentatus Wheat yield (t/ha) ZT+residue removal (RR) 291 297.3 .75 ZT+2.5 t/ha residue 304.6 310.1 1.05 ZT+5.0 t/ha residue 214.8 214.6 2.58 Z+7.5 t/ha residue 190.9 134.6 2.46 ZT (RR) with sulfosulfuron+metsulfuron at 25+3g/ha 2.9 0.0 5.48 CT without herbicide and residue 466.7 7.5 1.22 CT with sulfosulfuron+metsulfuron at 25+3 g/ha 0.3 0.0 5.61 LSD (P=0.05) 83.5 67.4 .39 Table 3 :Effect of residue retention and herbicide on wheat in rice- wheat system Chhokar et al ., 2009 ZT=Zero tillage,Ct=Conventional tillage

29. 29 Table 4 :Effect of different herbicidal treatments on weed biomass in wheat during the winter seasons 2010-11 to 2012-13 Yadav et al., 2016 Abbreviations: fb, followed by; LSD, least significant difference; RM, ready-mix .

30. 30 Date of sowing Temperature ( O C) Germination(%) 5 4.50 10 77.33 15 85.95 20 82.90 25 35.82 30 4.05 CD 5% 1.36 Chhokar & Malik., 1999 Sowing date can be manipulated. In case of Phalaris minor , early sowing (before 15 th November) Table 5 :Effect of temperature on seed germination of Phalaris minor

31. 31 Cropping sequence Phalaris minor (No . / m² ) Rice-wheat (continuously for 10 years) 2350 Rice-wheat-rice-wheat-cotton-wheat 2125 Rice-berseem-sorghum-wheat 190 Rice-potato-rice-wheat 255 Cotton-wheat (continuously for 4-5 years) 39 Rice-berseem-rice-berseem-rice-wheat 29 Rice-winter maize-sorghum-raya-maize-wheat 19 Maize-sunflower-rice-berseem-rice-wheat 35 Rice-potato-chilli-potato-rice-wheat 24 Table 6 : Effects of crop rotation on population of Phalaris minor in wheat Banga et al ., 1997

32. 32 Wheat variety Germination % % inhibition over control WH-283 75.97 16.53 WH-533 63.74 29.96 WH-542 72.00 20.89 WH-711 88.98 2.23 PBW-343 74.78 17.83 HD-2687 87.20 4.19 UP-2338 75.81 16.70 HD-2329 75.22 17.35 PBW-233 80.31 11.76 WH-896 82.96 8.89 WH-912 74.48 18.16 Control 91.01 -- CD at 5% 6.69 -- Om et al ., 2002 Table 7:Allelopathic effect of different wheat varieties on the germination of Phalaris minor

33. CONCLUSION Weed infestation is one of the main biotic constraints in wheat production and productivity. For weed control most of the farmers depend on herbicides due to cost and time effectiveness compared to manual weeding. However, continuous use of same herbicides of similar mode of action resulting in the buildup of resistant population of weeds. The evolution of herbicide resistant weeds is a threat to wheat sustainability. Long term strategies to manage herbicide resistant weeds should include integration of non- chemical methods with chemical for sustainable wheat production.

34. NEED OF AN HOUR Weed management strategies need to focus on reducing selection pressure and delaying onset of herbicide resistance and thereby increasing the effective life of existing herbicides . Ecological weed management systems need to be designed to manage herbicide resistance in weeds . Farmers should be trained to adopt good agronomic practices, herbicide rotation, herbicide mixture, which can delay resistance development in weeds and minimize the negative impacts of resistant weed populations . Greater emphasis needs to be placed on farmer participatory research to further improve early detection and management of herbicide resistance in weeds .