Latest insights into parasite control

Understanding the fundamentals of parasite development, metabolism and function is fascinating in itself... but the real driving force behind all such research is HOW it can be applied to control these agricultural pests.
This was one of my favourite sections of the meeting and is a topic close to my heart. Here are some of the highlights for me from the session:

Precision control for Orobanche: The herbicide Glyphosphate can be used effectively to control Orobanche, yet can also induce damage for the host & environment and is expensive for small-scale farmers. Extensive studies in Carrot (a major crop in Israel) have identified that applying low doses of herbicide at 600 growing degree days (an early stage of Orobanche development) is the optimum time for treatment; later applications are significantly less effective (Cochavi et al. Neww Ya'ar Research Centre, Israel). Such "precision timing" enables limited stocks of herbicide to be exploited to their full potential, whilst minimising host damage. But how to estimate the developmental stage of a below-ground parasite? A comprehensive study of Orobanche infestation of tomato in Israel  demonstrated the potential of mathematical modelling to address such issues (Eizenberg et al. Newe Ya'ar Research Centre, Israel). For irrigated crop systems, the main constrain on Orobanche development is the soil temperature , rather than moisture availability. In this project, a "drone" device was used to provide aerial mapping of the infected fields - the images provided such good resolution, that the infection stage could be visually assessed (whilst avoiding the need for laborious ground-level assessment). By correlating this to real-time soil temperature data, a model was formulated which could calculate Orobanche development based on the soil temperature. Hence, these methods can empower farmers with the knowledge of when the parasite is most vulnerable to herbicide treatment.

Combining resistance to drought and Striga: when considering methods for parasite control, these should not be isolated from other environmental or biological challenges constraining production. This was demonstrated superbly in a study which quantified drought tolerance among cultivars developed originally for Striga tolerance (Menkir et al, International Institute of Tropical Agriculture IITA). Striga itself is adapted to thrive in regions erratic rainfall and plants weakened by drought have been shown to be more susceptible to infection. The most drought-tolerant cultivars were crossed to produce hybrids, some of which demonstrated an incredible yield increase under infestation conditions (in one case 4113 kg/ha compared to 875 kg/ha for the parent line). As the speaker noted, selecting for these plants could address the dual problem of low moisture availability and parasite control in a way akin to "carrying two goats on the same motorbike" (the image helped to explain this!). Nevertheless, it was noted that the selection mechanism may simply be for higher yielding lines if the relative loss of yield between well irrigated/drought or uninfected/Striga infested conditions was the same as that experienced by the parents. Based on the significant differences in yield however, I'm not sure the farmers themselves would be too concerned about this point.

Arbuscular Mycorrhizae to the rescue? Having based my final year Undergraduate literature review on Arbuscular Mycorrhizal Fungi (AMF), I am perhaps slightly biased towards their intricate lifestyle and benefits. These fungi form intricate symbioses with most plant species, providing nitrogen and phosphorous in return for photosynthate sugars; the development of this association was thought to be instrumental in allowing plants to first colonise the land. Louarn et al. (INRA, France), have demonstrated however, how AMF may also have a practical use in controlling agricultural parasites. Strigolactones are produced by plants to recruit AMF but these have also been exploited by parasites to induce germination (allowing parasitic seeds to remain dormant until an available host is in close proximity). AMF colonised sunflowers were shown to be less susceptible to infection by Orobanche, yet this may simply be a consequence of decreased strigolactone production (if the roots are already colonised, the need to recruit AMF is reduced). In accord with this, root exudates from AMF colonised roots show lower germination stimulation of Orobanche than non-colonised root exudates. However, complementing the AMF root exudate with the classical synthetic strigolactone GR24 did NOT fully restore germination to the level of application of GR24 alone, suggesting that AMF produce a germination inhibitor which passes into root exudates. Characterising this inhibitor could offer an exciting avenue of research into parasite control, at least for Orobanche cumana.

Finally, the most popular talk was "Shoot the mistletoe", which described the development of a novel mistletoe controlling device at the University of Sao Paulo, Brazil. Gregorio Ceccantini humorously described how, at a different scientific gathering, involving considerable consumption of alcohol, an idea was born to use an air-triggered paintball gun to fire pellets of herbicide at mistletoes attached to commercially important trees. Besides proving that scientists love their toys (also justified by the "drone" study above - we were treated to many videos of it in action), this method does actually seem to be effective! Perhaps a way for bored teenagers to work off aggression?