Genetic Improvement of Rice for Bacterial Blight Resistance: Present Status and Future Prospects

The growth of rice has been heavily challenged due to several abiotic and biotic factors. One among those factors is bacterial blight, which is caused due to Xanthomonas, which is one of the biggest biotic stress factors. This reduces the production rate of rice by around 20% to 50%. 

Resistance was planned on being introduced to the rice production at the host plant itself, which was one of the evident management strategies for tackling bacteria blight issues. However, achieving such resistance for diverse rice variants is quite difficult by using just the conventional approaches. 

Therefore, modern biotechnological tools were introduced for this purpose, especially for deploying molecular markers. These tools have helped in facilitating cloning, introgression or characterisation of the bacteria blight resistance genes and implementing them into the elite rice varieties. 

So far, around 46 such genes have been identified and were mapped from multiple root sources. Among these identified genes, 11 of them are now cloned and successfully characterised. Among all the other options, marker-assisted breeding is still one of the most outstanding approaches for improving bacterial blight resistance, either in combination with the genes or alone. 

In this article, you will get an insight into developments with respect to the use of genetic improvements for rice to be free from bacterial blight disease. So, read along till the end! 

What is Bacterial Blight in Rice?

Bacterial blight is considered one of the deadliest bacterial diseases that are found in cultivated rice. This disease has a record of destroying around 75% of all crops, which totals up to millions of hectares of rice. 

If the rice plant seedline is affected by the bacterial blight, then the infection will be first seen in the leaves. They will start to turn yellow and then to the straw colour. Later, the leaves will die. If this disease affects the mature plants, then the effects will be seen from the tillering to that of the panicle formation. 

In the start, the plant will appeal to be greyish green or green, and there will be water-soaked streaks visible over them. But, once the plant gets affected by this disease, yellowish lesions will be formed, and they will have uneven edges. In the final stage of this disease, a milky ooze will drip from the plant leaves, which will then be left to dry out. 

What are the Methods of Controlling Bacterial Blight Disease?

There are two standardised approaches for the cultivators to seek the rice improvement and make it resistant to bacterial blight disease. And that includes biological control and chemical methods. As far as biological remedies are concerned, there are no commercial products that can be applied directly over the plants to keep the rice free from this disease. But, there are some copper-centric products that might help you in reducing the symptoms but cannot control the disease entirely.

Similarly, chemical methods were also used for the process. Under this, the rice seeds were treated with some authorised antibiotics with copper sulfate or copper oxychloride, as per recommendations. But, in some countries, the use of these antibiotics is prohibited, for which you must check with the country guidelines as well. 

However, as biological solutions aren’t effective enough and chemical infusions might hamper the premiums of the rice quality, the need for genetic changes was introduced. 

Genetic Changes Made to Rice for Resisting Bacterial Blight

Genetic changes over time by scientists gave rise to the XA1 gene of rice, which is considered resistant to the race 1 Xanthomonas oryzae bacterial blight. With further identification and cloning of resistant genes, XA13 was introduced, which is a cloned recessive resistance gene which plays a major role in developing rice pollen. 

Upon running a detailed analysis of the XA13 gene, experts came to the conclusion that this dominant gene gets activated when the plant experiences any bacterial infection. The constitutive silencing of this cloned gene enhanced the ability of rice to resist bacterial blight but also resulted in pollen sterility and reduced the seed-setting rate. 

The XA13 gene, when mutated within the promoter region, the functions associated with bacterial blight were lost. After this, the expert researchers continued their search for the multiple genes that have the ability to control the resistance against bacterial blight, which has now become a boon to the standard or basmati rice breeders associated with gene pyramiding by the MAB. 

Different genes are used in combination to ensure utmost resistance to this deadly disease and plant only the rice seeds that are safe from it. Deploying the host plant resistance is the best ideology for handling biotic stresses. Breeding all the rice variants with resistance to various insect damage or diseases will increase the spectrum and durability. 

In combination with diverse genes brought together to introduce various resistances, a lot of bacterial blight and other disease-resistant rice seeds were developed. Hence, this is how genetic changes have helped improve the rice quality by saving them from losing out on nutrients or dying without the plants reaching maturity. 

Conclusion

This is a brief explanation of how the best basmati rice and standard rice has undergone genetic improvements for promoting bacterial blight resistance. Prior to introducing the resistant genes, the researchers tried developing biological products to minimise the effects by topical or root-level application. But that didn’t help too much extent, and the use of chemicals degraded the quality of rice, which was not something acceptable at all. 

Therefore, scientists took up the mantle and planned on introducing genetic improvements to the rice for not just resistance from bacterial blight but a lot of other diseases.