Experts’ Insight on Rice Seed Treatment: Challenges, Innovations, and Integrated Solutions

Similar to human growth, the germination of rice seeds and healthy growth rice seedlings are very important stages in the whole growth period of rice, which have a vital impact on rice yields. However, throughout the life of rice, from sowing to germination and to growth, it will be affected by various biotic or abiotic stresses.

By managing a variety of abiotic and biotic stresses, rice seed coating treatments can maximize seed germination and promote seedling growth. Rice seed treatment technology is a very complicated system, especially for areas where rice cultivation methods are diverse. Therefore, many factors need to be considered in all aspects to ensure the best integrated treatment solution for rice seeds.

Experts from leading companies in the rice seed treatment field invited by AgroPages jointly analysed the problems and challenges faced in the rice seed treatment process, and shared the solutions and practical experiences they have. Those participating are: Lu Liang, Product development manager, Seedcare China at Syngenta; Sally Li, SAT Technical Services Manager - Asia Pacific, Corteva; Liu Runfeng, Director of R&D Center of PilarBio, and Sheng Guangwei, General manager at Guangzhou Doctor Miao Biotechnology.

What are the main biotic and abiotic stresses that affect the germination and healthy growth of rice seeds?

Lu Liang:The main biotic stresses that affect the germination and healthy growth of rice seeds are seed-borne and soil-borne diseases (such as: rice bakanae disease, seedling rot, seedling blight), insect pests (thrips, plant hoppers), bird damage and weeds. In particular, diseases can cause serious seed rot and seedling rot under suitable conditions. In addition, bakanae disease - as one of the most important seed-borne rice diseases - has become increasingly serious in recent years, partly due to its resistance to conventional active ingredients such as prochloraz and phenamacril. What’s more, existing conventional products, limited by their short persistence, are not effective enough to control bakanae disease in the late season after transplanting, which seriously jeopardizes rice production. 

Abiotic stresses mainly include drought, low temperature, high temperature, salt-alkali, herbicide damage, and heavy metals. All of these adverse abiotic stress conditions have a negative effect on the germination and growth of rice seeds. For example, under drought conditions rice seeds cannot absorb enough water, resulting in failure to germinate, growth inhibition or even death at seedling stage.

Moreover, the above biotic and abiotic stress factors also interact with one another, resulting in a compound effect on the germination and growth of rice seeds. For example, the risk of pre-emergency herbicide damage to rice is significantly increased under flooding conditions.

Sheng Guangwei: Many factors, internal and external, affect the germination and healthy growth of rice. The primary factor is the seed itself. The germination rate of rice seeds is associated closely with seed genes, seed screening, bacteria amounts in seeds, natural aging in the seed storage environment, among others. In particular, carrying bacteria and aging on the part of seeds are primarily responsible for the decline in the germination rate of commercial seeds. 

The second factor is the germination environment of rice seeds. Diseases and pests in the soil will affect the germination of rice, which can also be affected by poor environments, such as low temperature, drought, and flooding. 

Thirdly, human farming operations will also affect the germination of rice, such as the use of inferior seed coating agents for seed dressing or soaking, too high pregermination temperatures, and excessive pregermination. With the improvement of the ecological environment and the scaling of direct-seeding rice, growers are troubled by rats, birds, rabbits and other animals which eat rice seeds.

What are the current mainstream rice seed treatment methods?

Liu Runfeng: The main methods include seed soaking, priming, seed dressing and seed coating. Seed soaking can kill germs and viruses carried on the surface of seeds. Seed priming is used to promote the initial germination of rice seeds through temperature and humidity regulation, so as to improve the germination rate after raising seedlings or sowing in the later stage. Seed dressing with chemicals does not require film formation, or special requirements for the falling rate of chemicals. The emphasis is on treating the seed surface, which is similar to disinfection of the seed surface. In modern agricultural plant protection methods, seed dressing is gradually being replaced by seed coating. Seed coating is seed dressing with seed treatment agent containing film-forming additives, so the effective components of pesticides are fixed on the surface of seeds, which seems like putting coats on rice seeds to resist exotic pests and diseases.

Lu Liang: At present, the mainstream rice seed treatment methods are chemical soaking and seed treatment. Chemical soaking refers to the addition of active ingredients treatment during rice soaking period, and its advantage is that the method is relatively simple. However, because most of the active ingredients are distributed in the seed soaking solution, the method is only suitable for the control of seed-borne diseases, such as bakanae disease, and its effect and persistence against diseases and pests after sowing are very short. Seed treatment requires the active ingredients to be uniformly coated on the surface of the seed. Because most of the active ingredients are concentrated inside and around the seed after sowing, seed treatment can control a wide spectrum of diseases and pests in a more comprehensive way than chemical soaking. In addition, some research institutes have explored the application of seed-pelleting on rice.

Sally Li: In Asia, farmers historically soaked rice seed in a pesticide solution because these chemicals were not designed for seed treatment application. Nowadays, seed applied treatments include various fungicide and insecticide treatments. Once growers started to understand the benefits of seed treatment, there has been a growing trend in utilizing seed treatments in rice seed to have a healthy start to the growing season. Farmers are looking for ease and convenience for rice cultivation, reducing the need to work under high temperatures and reduce labor costs from foliar or granular application in the field.

What are the differences in the treatment methods of rice seeds in different planting area? 

Sheng Guangwei: Take China as an example, the northeast region is the main rice producing area in China. Because of the low temperature in early spring, this area generally adopts the way of using seedling trays in greenhouses for growing seedlings, which is prone to bakanae disease, pythium rot, seedling blight, and physiological bacterial wilt. As such, the rice seed treatment agents for this area need to effectively control bakanae disease, and pythium rot, particularly bakanae disease.

In southern China, we have direct-seeding rice and seedling growing rice. Direct-seeding rice is gradually adopted by farmers because of its time-saving and labor-saving features. Direct-seeding rice generally adopts direct seeding after seed soaking and pregermination, or even adopts direct seeding of dry seeds. During the planting process, rice is particularly susceptible to infestation by pests, especially borers, thrips, plant hoppers, etc., which requires the selection of insecticidal seed coating agents with an effective control effect on pests for coating. Some ecologically sound areas have a demand for repelling birds and rats.

What crop protection and nutrition products are applied in rice seeds? What are the target disease and pests?

Liu Runfeng: Rice seed treatment agents are usually compounded with insecticides and fungicides, which can kill insects and prevent diseases at the same time. Some plant growth regulator products are also used for seed treatment. Common fungicides include prochloraz, metalaxyl-M, fludioxonil, bronopol, hymexazol, etc., which are used to control rice blast, false smut, banded sclerotial blight, seedling rot, damping off, bakanae disease, bacterial leaf spot and flax leaf spot. The effective components of common pesticides include cartap, imidacloprid, carbosulfan, dinotefuran, clothianidin, thiamethoxam and pymetrozine, which target rice gall midge, rice planthopper and thrips oryzae. Common plant growth regulator products include S-ABA, compound sodium nitrophenolate, uniconazole, brassinolide, oxyenadenine and indoleacetic acid.

Sally Li: Insecticide seed treatments continue to grow. However, many farmers still rely on foliar or granular applications. In Asia, Corteva has introduced two rice seed treatment insecticides to the market in recent years. Lumivia™ 625 FS insecticide, with active ingredient chlorantraniliprole, is used to control stem borer and leaf folder. The second is Lumispance™ insecticide seed treatment, with the active ingredient pyraxalt, that protects a grower’s crops from brown planthopper in the paddy field. 

In the United States, rice growers utilize Dermacor^® X-100 seed treatment, with the active ingredient chlorantraniliprole, for protection against rice water weevil, Mexican rice borer, armyworm, rice stalk borer, sugarcane borer, and suppression of grape colapis.  

Lu Liang: All the seedcare products on rice sold and applied in China by Syngenta are intended for use in the method of seed treatment, and chemical soaking treatment is not recommended. At present, the main products are Apron Maxx^® (62.5 g/L Metalaxyl • Fludioxonil FS), Vibrance Maxx RFC^® (11% Sedaxane • Fludioxonil • Metalaxyl FS), and Cruiser Maxx B^® (25% Thiamethoxam • Fludioxonil • Metalaxyl FS). Depending on the needs from different regions, we provide disease and insect control solutions for the seedling stage, which can efficiently solve the damage caused by rice bakanae disease, seedling rot, seedling blight, and thrips. Meanwhile, these products can deliver the effect of crop enhancement.

Furthermore, in response to the needs of rice growers for light and simplified cultivation, Syngenta uses high-quality seed treatment products and technologies to help growers apply dry seed sowing technology on the seedling tray after seed treatment, thus skipping the traditional tedious soaking operation steps, especially pregermination. Currently, the annual application area of this technology exceeds more than 3 million mu (200,000 hectares) in China. This substantially saves multiple inputs, such as labor costs.

What is the effect of coating treatment on the emergence of rice seed?

Lu Liang: By managing a variety of abiotic and biotic stresses, rice seed coating treatment can maximize seed germination and promote seedling growth, ensuring full crop standing with strong roots and seedlings. However, it’s worth noting that the seed treatment tends to favor strong seeds over weak ones, so the seeds used for treatment should meet the national standard for improved varieties. If the rice seed is active enough, the application of seed treatment can effectively improve its ability to resist various stresses. If the seed is weak, negative performance may occur. In addition, high-quality seedcare products should be used for uniform coating to avoid some seeds failing to be good covered.

Liu Runfeng: In general, rice seeds coated according to the prescribed dosage and method have no adverse effect on the emergence of seedlings, and some of the active ingredients have certain growth-promoting effects. However, there are different kinds of surfactants, organic solvents and film-forming agents in different manufacturers. When encountering extreme weather or adverse conditions, there is occasionally phytotoxicity that causes low germination rates or rotten seeds. Therefore, when developing seed coating agents, we must perform safety tests under different conditions, including plot tests and safety tests in different regions and under different sowing conditions.

Sally Li: Corteva evaluates the impact of each active ingredient on seed quality before they bring it to market to ensure it does not negatively impact germination. 

Seed treatment insecticides and fungicides protect seed and seedlings in the early growth stages to reduce the negative impacts of diseases and insects. This results in a healthy start for the plants in the field, maximizing yield potential. 

What are the operation requirements of coated seeds when sowing? How do farmers avoid seed protection failure due to coating falling off?

Lu Liang: Coated seeds should be sown as soon as possible. If they need to be stored, they should be stored in a relatively ideal storage room or at room temperature to avoid accelerated aging due to high temperature and high humidity. Coated seeds must be placed in containers with clear labels. Do not put them together with food and feed to avoid accidental eating by children and livestock. 

At the time of sowing, the planting requirements are the same as for uncoated seeds. For safety reasons, however, make sure to wear protective clothing, wear protective gloves, and do not eat and drink water while sowing, or wipe eyes with bare hands. After sowing, wash hands and face with soap before eating.

To avoid coating dust off, first of all, it is necessary to ensure the use of high-quality seedcare products under suitable slurry volume ratio (1:25-50) and coating speed, and allow time for air drying if possible, to ensure uniform rice coated seeds with excellent film-forming properties and flow ability. Secondly, because physical friction is difficult to avoid across transportation, storage, and sowing, it is necessary to choose products with high adhesion and good wearability when coating. Finally, do not change water during soaking of the rice seeds that need to be soaked for pregermination after coating, so as to avoid active ingredients loss.

One more word here, Syngenta Seedcare Innovation Center (SCI) pre-tests and evaluates the coating quality of seedcare products, including uniformity, flow-ability, flow-ability and wearability, in an effort to avoid dust off through high-quality coating quality control.

Sally Li: Rice can be different from other crops because it often requires the seed to be soaked before sowing. There are two different recommended rice coating methods globally. First is dry seed coating similar to other crops where treatment can be done upstream, downstream, or on farm treatment. The second is applying the seed treatment after soaking the seed. The water solubility of active ingredients is the key to determine which method should be used. Lumivia 625 FS and Lumispance can be applied before soaking. In the U.S., Dermacor X-100 does not allow application after the seed is soaked and drained.

Treatment is carried out by rice seed companies, professional seed treatment providers, or on farm treatments following product labels. When treatment is applied by a professional, this can maximize the coating quality. Additionally, polymers can also be utilized to reduce abrasion and dust off to keep the active ingredients adhered to the seed. The other key point is the drying period, as seed coating takes time to fully dry after treatment, which can typically take 12 to 24 hours drying time before the treated seed should be sown or soaked. 

When handling coated seeds always follow the SDS and label’s PPE requirements to minimize exposure to chemicals.

Liu Runfeng: At present, it is more common that rice seeds are soaked and germinated after coating, which reduces the damage to buds due to coating, compared with the previous coating after germination. However, soaking seeds after coating to accelerate germination requires the film-forming agent to have excellent water resistance, so as to prevent the effective components from falling off after soaking in water, which reduces the effect of preventing pests and diseases. Therefore, high water resistance that ensures film-formation and excellent air permeability that ensures safety are the key indicators for screening film formers in seed coating agents.

Germination of treated rice seeds and crop establishment are usually impacted under the stress of chilling. What are ways to solve this problem?

Lu Liang: The reason why chilling stress has a great impact on rice seed germination and crop standing rates is exactly the typical manifestation of the interactions and superimposed effects of biotic and abiotic stress factors, as mentioned above. On the one hand, under a low temperature and cold environment, abiotic stress significantly inhibits rice seed germination and growth, and weakens seedlings. On the other hand, the slow growth of rice at low temperatures makes the suitable infection period of various seed-borne and soil-borne diseases longer, and weak seedlings caused by low temperature are more subject to diseases. After understanding the reasons, we can solve this problem in the following ways.

• To improve the ability of rice to resist seed-borne and soil-borne diseases: Use the seedcare products with both higher and lower fungus control and seed-borne and soil-borne diseases control. Meanwhile, make sure to select high-quality seedcare products with superior safety for rice seeds, given the low temperature stress of rice seeds under low temperature conditions.
  

  
  

• To improve the cold resistance of rice: Add biostimulants and microelements to the basic recipe of seed treatment, or select more cold-resistant varieties or pretreat seeds at low temperature.

• Improve the temperature conditions of cultivation facilities: Such as growing seedlings in greenhouses and using mulch for thermal insulation.

Sheng Guangwei: First of all, it makes sense to figure out the degree of chilling stress, that is, whether the low temperature is below or above zero, the low temperature below zero mainly occurs in the northeast region of China. Then, we should try our best to prevent rice from low temperature stress, which requires us to sow at appropriate times (according to the climate and solar terms), and avoiding premature planting. Of course, weather changes defy forecasts, especially in Northeast China, where sub-zero low temperatures often occur. Sub-zero low temperatures require farmers to keep their greenhouses warm, and even warmer to protect rice seeds and seedlings from sub-zero freezing damage.

For the low temperature above zero, the use of some low-temperature resistant seed coating agents can help protect the seeds well, maintain the vitality of the seeds in the low temperature environment, and prevent the seeds from damage by pathogens in the soil. If emergent rice seedlings suffer from continuous low temperatures, it will be necessary to supplement appropriate fungicides and nutritional foliar fertilizer to reduce the occurrence of physiological and pathological bacterial blight.

What are the new rice seed treatment products and formulations that your company has recently launched or is developing? What are the advantages of these products?

Lu Liang: Syngenta will launch new MOA seedcare products under the latest generation succinate dehydrogenase inhibitor (SDHI) class on rice, including 200 g/L cyclobutrifluram FS and 200 g/L pydiflumetofen FS (Shiyi), to be registered for the control of rice bakanae disease. These compounds act on the succinate dehydrogenase of complex II on the electron transport chain for mitochondria respiration in the cell, thereby affecting the electron transport system of the respiratory chain of the pathogenic fungi and impeding the energy metabolism of pathogenic bacteria and leading to their deaths. These compounds have high activity against Fusarium fujikuroi, and feature a very low dosage and long persistence.

These compounds have no cross-resistance with existing conventional active ingredient for bakanae disease. What’s more, because of their long persistence, they can better prevent and control the bakanae disease in the late season and ensure the yield. Syngenta’s new generation of SDHI seedcare products will redefine the market benchmark for the control of bakanae disease and lead this market over the next 10 years.

Liu Runfeng: The rice seed treatment product under research and development is Miaowanjin^® -25% clothianidin • metalaxyl-M • fludioxonil (mixed formulations of CS and SC for seed treatment agent), which, like Miaojianqiang, belongs to the Yunxin family. Through microencapsulation technology, beta-cypermethrin/metalaxyl-M is wrapped to alleviate the degradation of the compound itself in soil and the loss of metalaxyl-M due to its high water solubility. Moreover, the microcapsule wall material, as polymer material, has a certain film-forming effect and is beneficial to the adhesion of drugs on the seed surface.

Sheng Guangwei: The products we recently introduced to the market include: Boshidun. It features an excellent ability to prevent insects and diseases and to strengthen seedlings. With our patented slow-release film-forming agent technology, it is highly resistant to water soaking and the soaked seeds will not fade, so the duration of the agent is prolonged. Meanwhile, with Seed Doctor’s newly developed bird repellant technology, Boshidun can effectively reduce the probability of seeds being eaten by birds and protect seedlings without harming birds, thus truly realizing the harmony between man and nature.

Yilidan: With exceptional efficacy in controlling bakanae disease, it can effectively prevent rice bakanae disease in Northeast China.

We are also focusing on the technology to delay the aging of rice seeds, which can effectively reduce the decline in germination rates caused by the aging of rice seeds in circulation.

In your opinion, what is the best integrated solution for rice seed treatment today? What can we learn from your company’s advanced practical experience?

Liu Runfeng: Rice seed treatment technology is a very complicated system, and especially at present there are various cultivation methods of rice in China, so the best solution should have the following characteristics: 

(1) It adapts to the local mainstream cultivation methods or seed treatment methods. For example, the above-mentioned method of coating and then soaking seeds requires the products to have excellent water resistance, and when sowing rice seeds by machine, there are certain requirements for seed surface smoothness.

 (2) It has extremely high safety. Phytotoxicity in extreme environments can be effectively avoided by using environmentally-friendly surfactants, not using or using less organic solvents, and using efficient and safe film-forming additives. 

(3) It has reasonable collocation of effective components. Reasonable compounding of insecticides and fungicides can help achieve the synergistic effect of both pest and disease prevention. 

(4) It has nutrients. The nutrients, such as plant growth regulators, amino acids, bio-fertilizers, and various elements needed for seed germination and growth should be added to improve the stress resistance of seeds or promote rooting and growth.

Lu Liang: Again, take China as an example because of the wide areas of rice cultivation in China with a wide range of cultivation patterns and varieties, the quality and vitality of rice seeds are unstable. This means seed treatment places an ultra-high demand for the adaptability to complex production problems and safety therein. Therefore, I believe that the best integrated solution for rice seed treatment needs to do the best in every aspect of ″P (products)-A (application)-S (services)″, and PAS is also the core concept of ″different care, more than seeds″ that Syngenta seedcare has always adhered to.

Products: High-quality seedcare products should have a superior formula to ensure the safety of seeds, while exerting the effect of products and ensuring coating quality. In addition, they should have excellent control over product quality, including in terms of raw materials and production batch stability. In the meantime, the effective ingredients of low-toxicity and low-risk seed coating products need to be properly selected and reasonably combined to efficiently and pertinently tackle various biotic and abiotic stresses across different places. As it continues to innovate in the development of new products and formulations, Syngenta has been leading the development of rice seedcare in China, whether it is the development of Apron Maxx and Vibrance Maxx RFC, the classic rice seedcare products first registered, promoted, and applied in China, or the development of the latest generation of SDHI patented compounds specific for fusarium against rice bakanae disease in China, as well as the development and introduction of biological products against various abiotic stresses.

Application: It is necessary to provide the optimal coating solution for different rice seed treatment methods and mechanical equipment, such as product and product combination, coating time, rotation speed, slurry volume, and to ensure that the solution possesses the best coating uniformity, flow ability, and dust off, as well as comprehensive coating quality, including in seed safety under various environments and seed vitality conditions. Before the launch of the product, Syngenta SCI (Beijing) will conduct a comprehensive test on coating quality and seed safety in the above coating application indicators to ensure the high-quality application of Syngenta’s seed coating products and formulations. Meanwhile, Syngenta carries out customized testing for large customers, such as seed companies. In addition, Syngenta SCI, which has a global technical service network, serves Chinese customers with global coating application technology standards.

Services: It is necessary to stay oriented around the needs of customers and farmers and think like growers, such as in rice coating services, front-line technical guidance, safe medication management and training services. Take the coating service as an example. Because the channels face tight schedules and large workloads for coating, over the past more than ten years, Syngenta has provided and promoted excellent coating machine equipment to the channels, and established coating service centers in the channels to improve the coating efficiency of farmers, while ensuring coating uniformity and safety, and improving coating quality. Syngenta updates and replaces about 3,000 sets of coating equipment each year. At the seed company level, during each processing season the SCI dispatches salespersons to customers’ processing factories. They work with customers to debug the mechanical equipment to ensure that the coating solution performs well in the actual processing.

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This article was initially published in AgroPages' '2023 Seed Treatment Special' magazine.

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