Mechanisms and genetics of iron toxicity tolerance in African rice

大米是撒哈拉以南非洲(SSA)的主要主食，随着消费者偏好的变化和城市化，对大米的需求正在迅速增长。然而，目前国内生产仅占消费量的60%左右；SSA的进口占全球大米贸易的三分之一。因此，有各种国家和国际倡议，制定了雄心勃勃的计划，以提高整个南沙地区的产量。内陆山谷和其他地方有充足的适合农业气候的湿地，可以支持水稻面积的大规模集约和扩大。在雨季，水稻是低洼湿地上唯一可能的作物，因此它不会与其他作物争夺土地或水。然而，除了农业生产，即主要以水稻为基础的系统，包括鱼、蔬菜、水果和牲畜生产外，内陆山谷还为当地社区提供森林、饲料、狩猎和渔业资源，它们对于缓冲水源和作为生物多样性热点非常重要。农业生产的发展必须避免损害这些在当地和区域上重要的生态系统服务。这将需要改进水稻种质以及与这些系统相适应的营养和水分管理，以最大限度地减少所需的土地面积。它还需要评估整个南沙地区哪些地区最适合集约化和扩大以水稻为基础的农业，而不损害其他生态系统商品和服务的技术。据估计，随着种质和管理的切实改进，南沙内陆河谷总面积的不到10%将足以满足非洲对大米的总需求。但需要克服各种生物物理限制；其中最重要的是土壤健康问题铁(Fe)毒性。铁毒性是一组与淹水水稻土中高浓度还原亚铁(Fe(II))有关的严重限产疾病。这完全是水稻的问题，与淹水的厌氧土壤的生物地球化学有关。这在非洲水稻系统中是一个特别的问题，因为土壤的性质是高度风化、养分枯竭和富含铁氧化物，与亚洲低地的年轻冲积水稻土形成对比。它影响到SSA现有的和潜在的水稻面积的很大一部分(估计从面积的20%到60%不等)，并造成很大的产量损失(高达90%)。目前正在努力在非洲水稻和其他地方的育种和管理方案中利用非洲本土水稻种质对它的耐受性。但这受到这种疾病的复杂性以及对耐受性的潜在机制和遗传学缺乏了解的限制，这反映出它在亚洲水稻系统中相对不重要，而亚洲水稻系统是大多数水稻研究的重点。我们建议提供所需的生物科学和工具，以(A)阐明非洲本土种质对铁毒的耐受性机制和遗传学，以支持水稻育种和管理计划，以及(B)评估改进种质和管理的潜力，以提高整个南沙地区现有和新的以水稻为基础的耕作系统的生产力。我们将特别关注原产于非洲西部的水稻品种，以及原产于马达加斯加的水稻亚种。我们将结合土壤化学、植物生理学和分子遗传学方法，在非洲西部和马达加斯加进行实地研究，并在英国的受控环境和实验室工作的支持下进行。我们还将绘制南沙现有和潜在稻区不同类型铁毒的空间范围，并开发地理信息系统工具，以评估改善种质以及养分和水管理的潜力，以提高这些地区以水稻为基础的耕作系统的生产力。

Rice is a major staple food across sub-Saharan Africa (SSA) and demand for rice is increasing rapidly with changes in consumer preferences and urbanization. However, domestic production currently accounts for only about 60% of consumption; imports to SSA amount to a third of the global rice trade. Accordingly there are various national and international initiatives with ambitious plans for increasing production across SSA. There are ample agro-climatically suitable wetlands in inland valleys and elsewhere to support a large intensification and expansion of rice area. During the rainy season, rice is the only possible crop on low-lying wetlands, so it does not compete with other crops for land or water. However, besides agricultural production, i.e. mainly rice-based systems including fish, vegetable, fruit and livestock production, inland valleys also provide local communities with forest, forage, hunting and fishing resources and they are important for water buffering and as biodiversity hot spots. Development for agricultural production must be done in such a way as to avoid compromising these locally- and regionally-important ecosystem services. This will require improved rice germplasm and nutrient and water management suited to these systems, so as to minimise the land area required. It will also require technologies for assessing which areas across SSA are best suited to intensification and expansion of rice-based farming, without compromising other ecosystem goods and services. It is estimated that with realistic improvements in germplasm and management, less than 10% of the total inland valley area in SSA would be sufficient to meet the total demand for rice in Africa. But various biophysical constraints need to be overcome; one of the most important is the soil health problem iron (Fe) toxicity.Iron toxicity is a set of severely yield-limiting disorders associated with high concentrations of reduced ferrous iron (Fe(II)) in flooded paddy soils. It is exclusively a problem of paddy rice, linked to the biogeochemistry of flooded, anaerobic soil. It is a particular problem in African rice systems because of the nature of the soils, which are highly weathered, nutrient-depleted and rich in Fe oxides, in contrast to the young alluvial rice soils of the Asian lowlands. It affects a large part of the existing and potential rice area in SSA (estimates vary from 20-60% of the area) and causes large yield losses (up to 90%). There are currently efforts to exploit tolerance of it in the indigenous African rice germplasm in breeding and management programmes at AfricaRice and elsewhere. But this is constrained by the complexity of the disorder and by poor understanding of the underlying mechanisms and genetics of tolerance, which reflects its relative unimportance in Asian rice systems where most rice research has been focused. We propose to provide the bioscience and tools required to (a) elucidate the mechanisms and genetics of tolerance to Fe toxicity in indigenous African germplasm, in support of rice breeding and management programmes, and (b) assess the potential of improved germplasm and management to raise the productivity of existing and new rice-based farming systems across SSA. We will especially focus on Oryza glaberrima ('African' rice) species, indigenous to W Africa, and sub-species of Oryza sativa ('Asian' rice) indigenous to Madagascar. We will use a combination of soil chemistry, plant physiology and molecular genetics approaches with field work in W Africa and Madagascar, supported by controlled-environment and laboratory work in the UK. We will also map the spatial extent of different types of Fe toxicity in existing and potential rice areas across SSA, and we will develop GIS tools for assessing the potential for improved germplasm and nutrient and water management to raise the productivity of rice-based farming systems in these areas.