Periodic Reporting for period 1 - DARES (Associational resistance and neighbor recognition of in common dandelion roots) Reporting period: 2016-03-01 to 2018-02-28 Summary of the context and overall objectives of the project Plants grow and interact in diverse and heterogeneous communities. Interactions with their neighbors not only affect growth and reproduction but also defensive investment and herbivore resistance. So-called “associational” effects are common and widespread. While the impacts and mechanisms of associational effect on above ground plant-herbivore interactions have been studied extensively, they have rarely been investigated below ground. Investigating how roots recognize and respond to signals from neighboring plants is crucial to understanding plant community dynamics in nature. The overall research objective of DARES was to investigate the impact and mechanism of associational effect on root defenses of Taraxacum officinale (common dandelion) and on performance of its root feeder Melolontha melolontha (white grub). Specifically, we asked three questions: (1) How does the presence of neighboring plants affect T. officinale root defenses and M. melolontha larval performance? (2) What is the general mechanism of neighbor recognition by T. officinale - below ground volatiles or root exudates? (3) Which chemical compounds of neighbors does T. officinale respond to? Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far In this project, I used Taraxacum officinale (common dandelion) as focal plant and Poa pratensis (kentucky bluegrass) and Centaurea stoebe (spotted knapweed) as neighboring plants. Taraxacum officinale is a perennial herbaceous plant co-occurring with P. pratensis and C. stoebe in Eurasia. I furthermore worked with Melolontha melolontha (white grub) larva, which are highly polyphagous but prefer to feed on T. officinale. The project had three major scientific objectives: (1) Determine the impact of plant neighbor and neighbor attack on root metabolism of T. officinale and the performance of M. melolontha larvae, (2) Disentangle the chemical signals of neighbor recognition, below ground volatiles or root exudates, and (3) Identify chemical signals involved in neighbor recognition.Basically, I have fully reached objective (1) and (2) and made significant progress towards three over last two years from March 1, 2016 to September 30, 2017. I found that neighboring plant significantly affected T. officinale root defenses, which in turn influenced the performance of M. melolontha larvae feeding on T. officinale. This associational effect was triggered by both root volatile and exudates released by neighboring plant. Terpenes were identified as major active singles. So far, one paper entitled “Neighbourhood effects determine plant-herbivore interactions below-ground” has been published in Journal of Ecology in 2017 and also presented as a poster in 16th Symposium on Insect-Plant Relationships in France, one manuscript is being under review in Functional Ecology, and some raw data is being processed. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) Associational effect has been widely acknowledged as a major determinant in the plant-herbivore interactions in the field. My study provided first evidence that the associational effect is an important factor in below ground plant-herbivore interactions, extending the knowledge of associational effect into rhizosphere. This will strengthen and help to enhance the ERA’s position in this field. Furthermore, my results had important implications for weed and pest management below ground. Melolontha melolontha remains an important grassland and orchard pest in many regions of central Europe, and T. officinale is an undesired weed on lawns. Understanding T. officinale resistance against M. melolontha will contribute to identifying weaknesses in both organisms, which in the long run may help to reduce their negative impact on agriculture and recreational environments. Melolontha melolontha growth is affected by terpenes Melolontha melolontha growth is affected by root volatile and exudates emitted by neighboring plants Melolontha melolontha larvae cause serious damage to Taraxacum officinale in the field Melolontha melolontha growth is affected by neighboring plants
