Herbicide resistant (HR) biotech crops which include both the transgenic and non-transgenic ones are being grown in several countries for over 24 yr. Transgenic biotech crops are derived when an exogenous herbicide-resistant gene/s from non-plant sources is/are inserted into the desired crop plant. When the inserted genes stably integrate and express in the plant genome, the concerned plant behaves like a normal plant but with the acquired character, i.e. herbicide resistance. On the other hand, the non-transgenic biotech crops are generated for some herbicides (ALS-inhibiting and ACCase-inhibiting cyclohexane-diones) by selecting for target mutations in plant populations or by tissue culture or by mutation breeding. HR varieties have been developed for soybean, maize, cotton, canola, wheat, rice, sugar beet, alfalfa, etc. while the herbicides included glufosinate, dicamba, 2,4-D, phenmedipham, paraquat, imidazolinones, mesotrione, sulfonylureas, etc.
About 190 million ha around the world have been under HR transgenic crops in 2017. Around 80% of this area was under HR ones either alone or stacked with insect resistance. Biotech crops have made a positive contribution to global crop production and the economies of farmers, while they certainly raised concerns about biosafety to consumers. Several countries led by USA have widely adopted HR biotech crops, while India has been growing only the insect-resistant (IR) Bt cotton since 2002. With adoption of Bt varieties, the country has achieved a great stride in cotton production, accounting for a quarter of market share in global cotton production in 2017. Although no HR biotech crop is adopted in India, it is grown illegally by farmers in key cotton-growing states.
The concerns and limitations about HR biotech crops are related to agro-ecology, evolution of herbicide-resistant weeds, food safety, soil ecosystem, coexistence of biotech and conventional crops, socio-economic consequences, coexistence of biotech and conventional food products, etc. This paper also discusses management of HR biotech crops in greater detail.