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Plant breeding techniques and emerging evolution

Plant breeding techniques and emerging evolution

Food and nutritional security, sustainable agriculture and climate change are the most important issues to worry about these days. Many research works have been done till now to ensure the food security of world population which is addressed as the second goal among 17 UN sustainable development goals. Many experiments by the scientists are done to date including fruitful and futile ones. Techniques like breeding and genetic engineering have gained popularity among scientists to meet up the food requirement of ever increasing population. Emergence of green revolution has saved millions of lives so far. Majority of the scientists praised those innovations while some opposed. There are many opinions regarding the different techniques in the field of crop science mentioned in different articles. Here I am summarizing a review article by Deepak Pental (Pental, 2019) for the GNOBB readers, in which he upheld his opinions concerning some techniques mostly used to modify crops for better productivity. In his article, he mentioned that the most revolutionary developments during 20th century were Systematic pure-line breeding and Hybrid breeding. Real miracle happened in the field of crop science through the use of dwarfing genes and hybrids in cereal crops like wheat and rice. First dwarf variety Norin 10 was developed by a Japanese breeder Gonjiro Inazuka using Rht1 and Rht2 genes which first released for cultivation in Japan in 1935. After that, use of Rht (reduced height) genes like Rht1, Rht2 and Rht8 for breeding higher-yielding winter wheat varieties increased wheat yields from 1.3 tonne/ha in 1930 to 5.2 tonne/ha by the 1980s. The work of breeder Gonjiro Inazuka was followed by scientist O. A. Vogel who incorporated the dwarf trait into American spring wheat and Norman Borlaug who developed varieties which were photoperiod-insensitive and disease-resistant besides having the dwarf character. These varieties saved Mexico from impending food crisis and North India from prevailing famine-like condition in 1965. Another promising invention was yield-increment of maize in USA from 1.6 tonne/ha in 1936 to around 10.9 tonne/ha currently in USA; only after hybrids were introduced. China has raised yield potential of rice to more than 10 tonne/ha through hybrids recently. Other breeding techniques like polyploid breeding and mutation breeding were not among the successful techniques according to the article writer. As for reference he mentioned a human-made polyploid (Triticale), which was developed using the genomes of rye and wheat. This crop was supposed to out-yield wheat which was grown 220 million hectares (m ha) globally compared to 4.2 m ha triticale as reported in 2016. Mutation breeding is another method which became popular in the 1960s and 1970s mostly in developing countries was also alluded as a failure in the article. Reasons that obviated this technique to be a successful one were: mutagenic agents used to induce mutations causes multiple mutations in the genome. It is difficult to separate a desirable mutation from sundry mutations, which if retained would cripple the yield potential of the target crop. Another point is that, after inducing any mutation, the mutagenized material is crossed with the elite lines. So, the contribution of mutation is unclear as the changes in final released variety may be driven by recombination. All the methods that described above are applied to increase yield while yield protection is the most critical challenge to fight with. Plant genomes undergo repeated number of changes like polyploidy, genome enlargement/shrinkage, acquisition of resistance conferring R genes and their allelic variations. On the other hand, the major identified objectives responsible for yield loss are pests and pathogens which also develop resistant over the time. Creating heterogeneous agronomic conditions and applying crop rotation can help to overcome resistant to a little extent. From the writer’s point of view, engineering plants with resistance conferring R-genes against specific pest/pathogen is an excellent solution so far (i.e. Bt cotton). Genetic engineering (GE) technologies allow gene sourcing from a wider gene pool and also help to avoid the problem of linkage drag while transferring genes from the wild relatives to crop plants. Not only to develop resistance, GE technologies like tilling and CRISPR/Cas system have been used to produce advanced varieties of crops with better potential. During the last 40 years, invention of extensive biological software like molecular markers (for more efficient selection of recombinants), a vast repertoire of genes and their promoters (for expression modulation) and GE methodologies have given strength to tackle the challenges unmet with conventional recombination breeding. Development of GE mustard, which was later followed by GE rapeseed in 1966, produced millions of tonnes of oil and meal that consumed by humans and livestock without any consequential untoward effects. In the past couple of years, very involved review of GE technologies on released transgenic crops by the National Academy of Sciences, USA; American Association for the Advancement of Science; the Royal Society, London etc. has strongly stated and come to the conclusion that the GM crops are not necessarily more risky than conventional plant breeding technology. If we look back on history, it also claims that destruction of the science of genetics and plant breeding was a major reason to Soviet agriculture perform badly (around 1930s with the death of greatest geneticist Nikolai Vavilov). To feed around 7.7 billion global population, climate-resilient agriculture is the mandatory requirement which demands human ingenuity and rational resource management at its best. Logical reasoning and avoidance of misconceptions can exhort the scientific community to excel in agricultural R&D by the proper use of S&T to enhance crop productivity, save natural resources and all for the ultimate betterment of mankind.

Reference:

Pental, D. (2019). When scientists turn against science: exceptionally flawed analysis of plant breeding technologies. Current Science 117, 932-939.

Photo credit: US Wheat Associates website

 

Written by:

Dola Karmoker

Research Associate, PlantBiotechnology laboratory, Department of biochemistry and moelcular Biology, University of Dhaka

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