HERBICIDE RESISTANCE PLANTS

Herbicide Resistance plants



Herbicide Resistance plants

Introduction

In the past two decades, evolution of newer herbicides provided wider user choice. Selection of most promising prudent products intensified in use followed by genetically induced herbicide resistant crops. This is how the broad-spectrum herbicides created a great deal of impact on the stakeholders. It has been an established fact that weeds reduce farm yields and farm income drastically. Among all other weed control practices, herbicides alone is easy prompt, most effective and economically acceptable mean(Andow Hutchinson 1998 ); therefore, herbicides are overwhelmingly used by the farmers. Agriculture world over should have experienced a drastic shortfall in overall crop yields should herbicide availability be limited. Now, when the herbicide use gained a momentum and has been popularized as a formal input tool particularly in mechanized large holdings and commercial farming, the loss of herbicide effectiveness due to selection of herbicide-resistant weed populations has a negative impact on farmers. Herbicide resistance is the inability of a herbicide to effectively control a weed species that was previously controlled by the same herbicide. Herbicide resistance is detected when a biotype within a weed species possessing a resistant trait increases in abundance while susceptible biotypes are controlled by use of the same herbicide. The resistant trait is inheritable and therefore, is passed from one generation to the next. Once a herbicide-resistant population has been selected for, the likelihood of the weed population reverting back to a population dominated by the susceptible biotype is low. Resistant weed population becomes a serious constraint because it develops far faster (in 3 to 5 years) than the time and money investment on research, testing and registration for another newer chemical that meet modern environmental and health regulatory standards. As a result, herbicides with a new mode of action will not likely serve as a solution for herbicide-resistant weed populations. Therefore, it is absolute important that the herbicide options presently available be maintained through sound product stewardship. Stewardship implies that whoever produces, sells, or uses herbicide, exercises all precautions for minimizing any undesirable effects of the herbicide, including selection of resistant biotypes(Zhu T, et al 1999). 

Discussion

A group of researchers from Pioneer Hi-bred International recently produced lines of maize with resistance to the herbicide Lightning (a mixture of imazethapyr and imazapyr)1. On the surface, this is an unremarkable event. After all, resistance to these and similar herbicides has previously been produced in maize and other crops using either conventional breeding or genetic engineering strategies. However, what is unusual about the new maize lines is not the fact that they are resistant to these herbicides, but rather the method that was used to confer the resistance: a precise replacement of a single amino acid in the endogenous herbicide target enzyme(Patankar Giri Harsulkar Sainani Deshpande Ranjekar Gupta 2001, 31, ).

The herbicides imazethapyr and imazapyr are members of the imidazolinone herbicide family, which, along with the sulfonylureas (and a few newer herbicide families), act on plants through the inhibition of the enzyme acetohydroxy-acid synthase (AHAS). AHAS is a key enzyme in the synthesis of the branched chain amino acids_valine, leucine, and isoleucine; so disruption of the activity of this enzyme leads ...