Moving the corn belt northward: identifying key ultrastructural and physiological markers which provide chilling and frost stress resistance to enhance the breeding process

玉米（Zea mays L.）是具有重要经济价值的冷霜冻敏感作物。 玉米是全球第一大作物（2014年超过980，000，000公吨），其次是水稻、小麦和大豆（http：//www.statcan.gc.ca/pub/96-325-x/2014001/article/11913-eng.htm）。 仅在美国（约占世界产量的三分之一），2014年玉米的农场价值为520亿美元。 自2004年以来，玉米价格在十年内翻了一番多。 2014年，加拿大在全球玉米产量中排名第九（美国农业部）。 在加拿大，玉米是第三大最有价值的作物，从1971年到2011年，玉米生产面积翻了一番。然而，温暖的温度和漫长的生长季节是其生产面积的主要决定因素，因此，萨斯喀彻温省等地区拥有加拿大40%以上的可耕地，仅占加拿大玉米生产面积的0.3%。 因此，缺乏低温和霜冻胁迫抗性是限制整个草原谷物玉米生产的主要永久性限制因素。尽管进行了大量的研究工作，但在提高玉米的低温胁迫耐受性（低温和冷冻）方面尚未取得重大进展。 这可能与关注生长的早期阶段（几天龄的幼苗）、缺乏将对比基因型并入实验系统和应激施加方法（没有预先冷驯化的冷休克暴露）有关。 大草原生长季节的夜间温度通常为10 ℃，植物在这种条件下有可能适应寒冷。籽粒灌浆是秋季低温胁迫风险最高的阶段，对产量影响最大。 本研究的目的是确定关键的超微结构和生理标记，这是与低温和霜冻胁迫的抗性在营养和灌浆阶段在应激敏感和耐受谷物玉米线，没有事先驯化冷。 然后，这些鉴定的标记可用于通过靶向选择来提高育种过程的效率。 这项研究建立在两个正在进行的玉米抗冷和抗冻性研究项目的基础上，并对这两个项目进行了补充。

Corn (Zea mays L.) is a chilling and frost sensitive crop of significant economic value. Corn is the number one crop worldwide (over 980,000,000 million metric tonnes in 2014) followed by paddy rice, wheat and soybeans (http://www.statcan.gc.ca/pub/96-325-x/2014001/article/11913-eng.htm). In the USA alone (accounting for about one-third of world production), the farm gate value of corn was $52 billion in 2014. Corn prices have more than doubled in the ten years since 2004. In 2014, Canada was ranked 9th in corn production worldwide (USDA). In Canada, corn is the third most valuable crop and production area doubled from 1971 to 2011. However, the necessity of warm temperatures and a long growing season are the main determinants of its production area and thus regions such as Saskatchewan, which has over 40% of the arable land in Canada, has only 0.3% of Canada's corn production area. Accordingly, lack of both chilling and frost stress resistance are the primary perpetual constraints limiting grain corn production across the prairies. In spite of a large research effort, significant advancements in elevating low temperature stress tolerance (chilling and freezing) in corn have not been achieved. This may be related to the focus on the early stage of growth (few days old seedlings), lack of incorporation of contrasting genotypes into experimental systems and method of stress application (cold shock exposure without prior cold acclimation). Night temperatures during the growing season in the prairies are typically 10C and plants have potential to cold acclimate under these conditions. Grain filling is the stage of highest risk to low temperature stress in the fall and has the greatest impact on yield. The goal of this study is to identify key ultrastructural and physiological markers which are linked to chilling and frost stress resistance during both the vegetative and grain filling stages in stress sensitive and tolerant grain corn lines with and without prior acclimation to cold. These identified markers can then be used to enhance the efficiency of the breeding process through targeted selection. This study builds upon and complements two ongoing research projects on chilling and frost resistance in corn.