Genetic variation in yield under hot ambient temperatures spotlights a role for cytokinin in protection of developing floral primordia.

Unusually hot ambient temperatures (HAT) can cause pre-anthesis abortion of flowers in many diverse species, limiting crop production. This limitation is becoming more substantial with climate change. Flower primordia of passion fruit (Passiflora edulis Sims) vines exposed to HAT summers, normally abort. Flower abortion can also be triggered by gibberellin application. We screened for, and identified a genotype capable of reaching anthesis during summer as well as controlled HAT conditions, and also more resistant to gibberellin. Leaves of this genotype contained higher levels of endogenous cytokinin. We investigated a possible connection between higher cytokinin levels and response to gibberellin. Indeed, the effects of gibberellin application were partially suppressed in plants pretreated with cytokinin. Can higher cytokinin levels protect flowers from aborting under HAT conditions? In passion fruit, flowers at a specific stage showed more resistance in response to HAT after cytokinin application. We further tested this hypothesis in Arabidopsis. Transgenic lines with high or low cytokinin levels and cytokinin applications to wild-type plants supported a protective role for cytokinin on developing flowers exposed to HAT. Such findings may have important implications in future breeding programmes as well as field application of growth regulators.

Shielding Flowers Developing under Stress: Translating Theory to Field Application.

Developing reproductive organs within a flower are sensitive to environmental stress. A higher incidence of environmental stress during this stage of a crop plants' developmental cycle will lead to major breaches in food security. Clearly, we need to understand this sensitivity and try and overcome it, by agricultural practices and/or the breeding of more tolerant cultivars. Although passion fruit vines initiate flowers all year round, flower primordia abort during warm summers. This restricts the season of fruit production in regions with warm summers. Previously, using controlled chambers, stages in flower development that are sensitive to heat were identified. Based on genetic analysis and physiological experiments in controlled environments, gibberellin activity appeared to be a possible point of horticultural intervention. Here, we aimed to shield flowers of a commercial cultivar from end of summer conditions, thus allowing fruit production in new seasons. We conducted experiments over three years in different settings, and our findings consistently show that a single application of an inhibitor of gibberellin biosynthesis to vines in mid-August can cause precocious flowering of ~2-4 weeks, leading to earlier fruit production of ~1 month. In this case, knowledge obtained on phenology, environmental constraints and genetic variation, allowed us to reach a practical solution.