Claudio Screpanti

Strigolactone derivatives for potential crop enhancement applications.

New technologies able to mitigate the main abiotic stresses (i.e., drought, salinity, cold and heat) represent a substantial opportunity to contribute to a sustainable increase of agricultural production. In this context, the recently discovered phytohormone strigolactone is an important area of study which can underpin the quest for new anti-stress technologies. The pleiotropic roles played by strigolactones in plant growth/development and in plant adaptation to environmental changes can pave the way for new innovative crop enhancement applications. Although a significant scientific effort has been dedicated to the strigolactone subject, an updated review with emphasis on the crop protection perspective was missing. This paper aims to analyze the advancement in different areas of the strigolactone domain and the implications for agronomical applications.

Strigolactam: New potent strigolactone analogues for the germination of Orobanche cumana

Very recently, strigolactones have been conclusively identified as phytohormones. The progresses achieved in this field are culminating in the identification of the molecular receptors involved in the signal transduction mechanism. The exact mechanism of the mode of action of strigolactones still remains to be fully elucidated and we were interested to gain some insight into the mechanism of action of strigolactones by selectively modifying the reactivity of the lactone C-ring. Therefore, we report here the synthesis of strigolactams 1 and 16 and their surprisingly good activity on the germination of Orobanche cumana parasitic weed seeds.

Simplified strigolactams as potent analogues of strigolactones for the seed germination induction of Orobanche cumana Wallr

BACKGROUND Strigolactones play an important role in the rhizosphere as signalling molecules stimulating the seed germination of parasitic weed seeds and hyphal branching of arbuscular micorrhiza, and also act as hormones in plant roots and shoots. Strigolactone derivatives, e.g. strigolactams, could be used as suicidal germination inducers in the absence of a host crop for the decontamination of land infested with parasitic weed seeds. RESULTS We report the stereoselective synthesis of novel strigolactams, together with some of their critical physicochemical properties, such as water solubility, hydrolytic stability, as well as their short soil persistence. In addition, we show that such strigolactams are potent germination stimulants of O. cumana parasitic weed seeds and do not affect the seed germination and the root growth of sunflower. CONCLUSIONS The novel strigolactam derivatives described here compare favourably with the corresponding GR-28 strigolactones in terms of biological activity and physicochemical properties. However, we believe strigolactone and strigolactam derivatives require further structural optimisation to improve their soil persistence to demonstrate a potential for agronomical applications.

Strigolactones and parasitic weed management 50 years after the discovery of the first natural strigolactone strigol: status and outlook

1 BRIEF HISTORY This year, it will be 50 years since the first scientific report was published on the isolation and characterization of strigol, a potent stimulant of the germination of Striga lutea seeds1. The paper from Cook and collaborators paved the way for the discovery of a range of similar molecules, collectively called strigolactones, from many different plant species, that stimulate the germination of the seeds of root parasitic plants. The discovery that strigolactones are also host detection signals for arbuscular mycorrhizal fungi and have an endogenous role as plant hormone opened up an exciting new area of research and today the strigolactones, with their multiple roles in rhizosphere signaling including but not limited to parasitic weeds and with new additional functions as plant hormone, are a hot topic. Particularly in the last few years, we have witnessed an exponential increase in scientific publications on the strigolactones (figure 1), which highlights the strigolactones as a very quickly evolving domain in plant science. Similarly, the substantial increase in numbers of patents filed (figure 2) on the use of strigolactones demonstrates the increasing commercial interest, particularly in agriculture. Among the different applications, the use of strigolactones to control parasitic weeds remains one of the main endeavours. Indeed parasitic weeds of the Striga and Orobanche genera, represent a serious threat to agriculture in several regions of the world and there is therefore an urgent need to find reliable solutions. Already in 2009 this journal devoted a special issue to this topic specifically on “managing parasitic weeds: integrating science and practice” and highlighted several of the associated challenges2. Since then the domain has evolved so much that a first international congress on strigolactones was organised in Wageningen in March 2015 (http://www.strigolactones.org/).

Aerial and Ground Based Sensing of Tolerance to Beet Cyst Nematode in Sugar Beet

The rapid development of image-based phenotyping methods based on ground-operating devices or unmanned aerial vehicles (UAV) has increased our ability to evaluate traits of interest for crop breeding in the field. A field site infested with beet cyst nematode (BCN) and planted with four nematode susceptible cultivars and five tolerant cultivars was investigated at different times during the growing season. We compared the ability of spectral, hyperspectral, canopy height- and temperature information derived from handheld and UAV-borne sensors to discriminate susceptible and tolerant cultivars and to predict the final sugar beet yield. Spectral indices (SIs) related to chlorophyll, nitrogen or water allowed differentiating nematode susceptible and tolerant cultivars (cultivar type) from the same genetic background (breeder). Discrimination between the cultivar types was easier at advanced stages when the nematode pressure was stronger and the plants and canopies further developed. The canopy height (CH) allowed differentiating cultivar type as well but was much more efficient from the UAV compared to manual field assessment. Canopy temperatures also allowed ranking cultivars according to their nematode tolerance level. Combinations of SIs in multivariate analysis and decision trees improved differentiation of cultivar type and classification of genetic background. Thereby, SIs and canopy temperature proved to be suitable proxies for sugar yield prediction. The spectral information derived from handheld and the UAV-borne sensor did not match perfectly, but both analysis procedures allowed for discrimination between susceptible and tolerant cultivars. This was possible due to successful detection of traits related to BCN tolerance like chlorophyll, nitrogen and water content, which were reduced in cultivars with a low tolerance to BCN. The high correlation between SIs and final sugar beet yield makes the UAV hyperspectral imaging approach very suitable to improve farming practice via maps of yield potential or diseases. Moreover, the study shows the high potential of multi- sensor and parameter combinations for plant phenotyping purposes, in particular for data from UAV-borne sensors that allow for standardized and automated high-throughput data extraction procedures.