Host Plant Resistance, integrated with other IPM approaches, is an important part of the proposed ASEAN Resistance Management Plan work. But what does this mean and why is it important to the ASEAN Action Plan on Fall Armyworm?
In this Blog we ask international expert, Dr Prasanna Boddupalli, from CIMMYT’s Global Maize Program and CGIAR Research Program MAIZE to explain.
What do we mean when we talk about fall armyworm (FAW) and "host plant resistance"?
PB: “Host plant resistance” can be defined as “the collective heritable characteristics by which a plant reduces the possibility of damage by an insect-pest or a pathogen and/or the ability of the plant to recover or repair after the injury occurs, resulting in minimum reduction in yield as compared to other cultivars of the same plant species under similar conditions”.
What is the difference between native genetic resistance and Bt-based transgenic resistance to FAW?
PB: Host plant resistance (HPR) could be either native genetic resistance (with sources of resistance available within the plant’s own gene pool) or transgenic resistance (where a gene or combination of genes from an external source(s) is transferred to make the host plant resistant to an insect-pest like FAW). Genetically speaking, native genetic resistance to FAW is polygenic i.e., controlled by several genes, and does not confer high levels of resistance compared to Bt-based transgenic resistance, which is either monogenic (conferred by a single gene from an external source) or oligogenic (conferred by 2-3 genes from an external source).
We must also recognize that native genetic resistance, once identified, can be used in crop breeding programs similar to other traits and improved varieties developed and deployed to farming communities, while development of transgenic/Bt crops with resistance to an insect-pest like FAW requires access to specific intellectual property and significant institutional expertise to develop such varieties, before they are tested for their biosafety and efficacy, and released by regulatory authorities.
Why is HPR (integrated with other IPM approaches) an important part of the proposed ASEAN Resistance Management Plan work? Are native genetic resistance and Bt-based resistance complementary?
PB: The Bt approach, with an appropriate “event” against the target insect-pest like FAW, can indeed result in high levels of resistance in a host plant like maize. While this offers greater protection from the insect-pest, it also exerts high level of pressure on the insect to evolve resistance against the Bt event.
That is the reason why many individual Bt events released against FAW in the Americas had a life span of 3-6 years. “Insect resistance management” is, therefore, extremely important to delay the evolution of resistance through appropriate management practices especially when Bt varieties are released for commercialization.
Although Bt events could be integrated in any genetic background and released for offering protection against FAW, I strongly believe that in the interest of insect resistance management, it is highly prudent to complementarily use native genetic resistance and transgenic resistance. That means, instead of using any elite genetic background, we must deliberately introgress* the transgene(s) into an elite genetic background with native genetic resistance to FAW. This approach will then complementarily bring to the fore the polygenic native genetic resistance plus the monogenic/oligogenic transgenic resistance, which will make evolution of resistance in FAW against much less probable or significantly delayed.
* transfer of genetic material from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species.
What are the opportunities for Southeast Asia to develop Asia-adapted native genetic resistant maize germplasm (inbred lines and hybrids) for the management of FAW? And how long would it take to develop, if we had adequate investment and resources targeted on this?
PB: CIMMYT’s elite maize inbred lines with native genetic resistance to FAW have been already shared with several institutions across Asia as international public goods. These can be used as sources of resistance by the breeding programs to come up with Asia-adapted, FAW-tolerant/resistant maize hybrids.
Efforts are already underway by CIMMYT maize breeding team based in India to develop such hybrids. With adequate investment and resources (e.g., FAW mass-rearing plus screenhouses to identify germplasm with resistance under FAW artificial infestation) and extensive on-station and on-farm testing for key traits preferred by Asian farmers, it is possible for breeding institutions to develop elite Asia-adapted maize hybrids with native genetic resistance to FAW within the next 2-3 years.
This is then followed by varietal release/registration, based on respective country regulations which may take 1-2 years before the seed of the varieties reach farming communities. While this is the normal process, it is also possible to accelerate the process of development of elite Asia-adapted maize hybrids (e.g., by speed breeding coupled with molecular markers-based or genomic selection) and fast-track the varietal release process, if the regulatory authorities consider data generated by breeding institutions appropriately (e.g., on-station and on-farm data from similar agro-ecologies). This is indeed highly relevant as the pest is causing significant economic damage and is of high concern to the stakeholders.
Southeast Asia is expected to suffer more intense, more frequent drought conditions as a result of climate change at the same time that FAW and other pests threaten crops. What are the opportunities to develop new maize varieties for this region that can respond better to multiple threats such as FAW and drought?
PB: The probability of success of any elite variety will be high if it meets the requirements of the farmers in the target market segment. Climate change is a reality, and there is no doubt that Southeast Asia is one of the highly vulnerable regions or “hot spots” for climate-induced variabilities and extremes. Resistance to FAW cannot work as a standalone trait but has to be part of the “trait package” relevant for the needs of maize smallholders in SE Asia. This is what we call “product profile-based breeding” to develop farmer-preferred and market-preferred varieties.
CIMMYT’s vast germplasm base suitable for tropical stress-prone environments, coupled with more than four decades of experience and success in breeding for climate-resilient traits, is therefore highly important for effectively responding to multiple threats like climate-related abiotic stresses like drought, heat and waterlogging, and biotic stresses like FAW and major diseases.
One can have comprehensive details on this topic from a review article we have published very recently (Prasanna et al. 2021, Beat the stress: Breeding for climate resilience in maize for the tropical rainfed environments. Theoretical and Applied Genetics, https://doi.org/10.1007/s00122-021-03773-7).
Given your experience in working on FAW management in Africa, what are your key tips for helping farmers better control FAW in Southeast Asia?
PB: There are several lessons/tips that we can learn from the experiences of FAW management in Africa and apply these in Asia, and vice versa.
1. FAW cannot be eradicated in the conducing environments of Africa and Asia. Moreover, there cannot be a single solution that can offer sustainable control. Therefore, we need to implement effective, science-/evidence-based management tactics around the IPM concept.
2. We need to think beyond narrow disciplinary and institutional boundaries. IPM stands not just as a technical concept; it is more about “Integrating People’s Mindsets”.
3. Solutions for FAW control are emerging from multiple fronts. We need to intensify our efforts to enable farmers’ access to well-validated technologies, and deploy these solutions in an integrated manner, depending on the socio-economic contexts of farmers, value chains, and cropping system landscape.
4. Early detection of the pest (especially damage symptoms in the field) is important for the smallholder farmer to take informed decisions on interventions. Note that there could be multiple generations of the pest in a maize crop season. So, one must not let the guard down throughout the crop season.
By combining good agronomic practices, host plant resistance, biological control, and environmentally safer pesticides, we can effectively overcome the pest.
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