Unravelling the effect of winter warming on flowering time, flower fertility and crop yield

Climate change is predicted to warm winters in western Europe between 2C and 8C above pre-industrial temperatures this century. It is well known that warm winters negatively affect the yield of perennial crops where incomplete chilling of flower buds in winter leads to weak bud break and fewer open flowers: indeed the requirement for winter chill generally determines the climate zones favourable for cultivation of temperate perennial crops. In Europe high yielding major arable crops are grown as winter annuals, that is they are sown in late summer or autumn and have a requirement for winter chilling to promote the transition to flowering in spring, a process known as vernalisation. However, we have recently shown that for the winter oilseed rape crop this vernalisation process actually happens in mid-autumn, followed quickly by the floral transition and formation of a flower bud in late autumn. We also showed that the stage of flower bud development corresponds to a period in the field where warm winter temperatures have a substantial negative affect on the UK yields the following summer. This raises the question of whether like perennials, winter annual crops have a requirement for chilling of flower buds to maximise crop performance in the following spring, and whether climate change is reducing yields in climate zones where winter chilling is not guaranteed. The preliminary data provided here provides compelling support for this hypothesis. Most specifically, we show that chilling of flower buds promotes earlier bud break in spring, and that winter warming of flower buds leads to production flowers in spring with obvious abnormalities and poor fertility.

This proposal uses a combination of physiology, molecular genetics, breeding and genomic approaches to understand the mechanism by which warm winters negatively impacts winter oilseed rape yields, especially in climate zones prone to warm spells during early winter when inflorescence development is taking place, such as the United Kingdom and China. Then we will use genomic approaches to breeding to clone genes in oilseed rape that may confer more resilient yields in growing seasons with warm winters, exploiting our previous discovery of one variety that we show has no significant yield response to temperature variation during inflorescence development. By introgressing these traits into elite germplasm we can determine whether climate change resilient genetics can be combined with modern high yielding lines to generate lines suitable for modern breeding programmes.

Winter annuals are generally accepted to germinate in summer or autumn and require vernalisation to promote the transition to flowering in response to the longer days and the warmth of spring. However, in WOSR we have shown that the vernalisation requirement for the floral transition is filled during October, mid autumn in the UK. Instead we show here that the chilling-responsive floral repressors known as MAF2-4, as well as two copies of the FLC gene, only respond to chilling after the floral transition, and provide evidence for a previously unknown second chilling response in flower buds which is also important for the control of flowering time and crop yields. This proposal aims to test the hypothesis that this second chilling response can be disrupted by warmth in early winter, and that lack of chilling enables persistence of these floral repressors during inflorescence development, causing the development flowers with obvious defects and poor fertility. This is accompanied by lower seed set and yield the following summer. We will use tissue specific inducible expression systems to fine tune expression of FLC and MAF4 in inflorescences and flowers and uncover the mechanism of this newly discovered response to temperature in winter crops. Then we will provide a platform for breeding yield resilience to warm winters through characterisation of a variety discovered through statistical analysis of past National List trial data to be yield insensitive to winter temperature variation. We subsequently found that this variety vernalises more quickly at warmer temperatures than other WOSR and has an unusual yield distribution across the inflorescence, each of which may underlie the yield resilience. By identifying the underlying genes and determining whether they can be breeding into elite cultivars, we aim to create germplasm useful for breeding increased climate change resilience into the UK WOSR crop.