By Adrish Dey, Research Fellow, ICAR-IARI, New Delhi
One speaks of fiber crops, the name that inadvertently comes to our mind is cotton. Of course, it is the most essential fiber crop globally. In our country, we observe three distinct agro-ecological regions where cotton cultivation occurs. When it comes to any large-scale agricultural production, pest management is quite a matter of concern. The situation is no different in cotton.
Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae) commonly known as the pink bollworm (PBW) has emerged as a threat to cotton cultivation in the southern and central cotton growing zones of India. They have developed resistance to Cry1Ac and Cry2Ab, the toxin protein genes obtained from the soil bacterium, Bacillus thuringiensis and genetically engineered in cotton. Additionally, they are expressing signs of resistance to certain insecticides and infesting late-stage cotton in these regions. Northern India is also not free from its menace. The oil extraction units procure cotton seeds from central and southern Indian states, which increases the possibility of spreading pink bollworm infestation in Northern India.
Understanding the genetic constitution of a pest population is very vital in determining its capacity to tolerate adverse climatic conditions and adoption to new conditions. Population genetic structure and genetic diversity define the level of adaptation of a population to environmental change and susceptibility to selection pressure.
To understand the genetic structure and diversity of this pest in India, scientists from the ICAR-Central Institute of Cotton Research, Nagpur conducted an extensive study by collecting Indian populations of P. gossypiella from three distinct cotton growing eco-zones of India spanning nine cotton growing states and forty-four major cotton growing districts.
The scientists compared 214 sequences of mitochondrial cytochrome oxidase subunit I gene of pink bollworm populations from different parts of India. They selected this mitochondrial DNA sequence region because it is maternally inherited, well conserved and evolves in a nearly neutral fashion, so it reflects the divergence times, which makes it a robust marker for determining genetic relationships and geographical studies. They identified 27 unique haplotypes in the three cotton-growing regions of India. The Pg_H1 haplotype was quite predominant representing nearly 14.68, 62.23 and 23.07% of total individuals in north, central, and southern zone populations, respectively. The second most dominant was the Pg_H2 haplotype.
Accurate assimilation and understanding of the genetic diversity of an insect pest are found essential to mitigate and improve its monitoring that further facilitates the implementation of need-based independent strategies. The scientists observed that the genetic diversity in the central zone was low compared to that of north and south whereas the entire population exhibited a low level of genetic diversity.
Furthermore, the scientists assessed the demographic history of the population and found evidence of population expansion or growth for the cotton PBW population from India. Overall, the haplotype network showed star-shaped cartography as characteristic of population expansion after a bottleneck, wherein newer mutations form groups of lower-frequency haplotypes budding from a central haplotype.
For further details, please refer to https://www.nature.com/articles/s41598-020-61389-1