Reviewing research priorities in weed ecology, evolution and management: a horizon scan.

Weedy plants pose a major threat to food security, biodiversity, ecosystem services and consequently to human health and wellbeing. However, many currently used weed management approaches are increasingly unsustainable. To address this knowledge and practice gap, in June 2014, 35 weed and invasion ecologists, weed scientists, evolutionary biologists and social scientists convened a workshop to explore current and future perspectives and approaches in weed ecology and management. A horizon scanning exercise ranked a list of 124 pre-submitted questions to identify a priority list of 30 questions. These questions are discussed under seven themed headings that represent areas for renewed and emerging focus for the disciplines of weed research and practice. The themed areas considered the need for transdisciplinarity, increased adoption of integrated weed management and agroecological approaches, better understanding of weed evolution, climate change, weed invasiveness and finally, disciplinary challenges for weed science. Almost all the challenges identified rested on the need for continued efforts to diversify and integrate agroecological, socio-economic and technological approaches in weed management. These challenges are not newly conceived, though their continued prominence as research priorities highlights an ongoing intransigence that must be addressed through a more system-oriented and transdisciplinary research agenda that seeks an embedded integration of public and private research approaches. This horizon scanning exercise thus set out the building blocks needed for future weed management research and practice; however, the challenge ahead is to identify effective ways in which sufficient research and implementation efforts can be directed towards these needs.

First Report of the Parasitic Plant Phelipanche aegyptiaca Infecting Kenaf in Israel.

Kenaf (Hibiscus cannabinus L.; Malvaceae) is an annual fiber crop that has recently been introduced as a niche crop in Israel, and grown mainly at areas with high summer temperatures. It is advantageous in crop rotation in these areas since it can rapidly accumulate biomass under high temperatures when other crops (e.g., tomato, sunflower, corn, and sorghum) cannot be cultivated. Additionally, the fact that it can be irrigated with waste water makes it attractive under these climatic conditions. Broomrapes (Phelipanche and Orobanche spp.) are chlorophyll-lacking obligatory root-parasitic plants that parasitize the root system of many field crops and vegetables (1). Parasitism by P. aegyptiaca has economic impacts on various crops belonging to several botanical families (e.g., Solanaceae, Apiaceae, Fabaceae, and Asteraceae). This parasitic weed is common in most agricultural areas in Israel including the coastal plain, Yisre'el Valley, the Jordan Valley, and the Negev Desert. High infection levels by P. aegyptiaca have result in a severe yield losses and quality reduction in these crops. Parasitism of P. aegyptiaca on kenaf was observed in September 2012 in a field located in Bet-Shean Valley (Latitude 32° 30' N; Longitude 35° 30' E; 105 m), with an average density of 0.7 plant/m2, in a total area of 0.3 ha. This crop was planted on May 2012 in plots that were previously affected. Infection did not lead to visible symptoms or damage to kenaf, but allowed seed production by the parasite. In order to verify that kenaf was a host of P. aegyptiaca, 10 samples of kenaf plants infected with P. aegyptiaca were taken to the lab and the root systems of the plant and the parasite were carefully washed. Cross-sections of the connection between kenaf and the parasite were taken and inspected for xylem connections under a compound microscope (BX61, Olympus) equipped with high-resolution digital camera (DP-70, Olympus), under 40× magnification. A clear xylem connection between the weed's tubercles and kenaf roots was observed, confirming the development of functional Phelipanche haustoria. To our knowledge, this is the first report of kenaf as a host for P. aegyptiaca. Kenaf has been reported to induce the germination of O. cernua in India (3). Cotton, another member of the Malvaceae, has also been reported to stimulate seed germination of O. minor (4) and P. aegyptiaca (2). However, to the best of our knowledge, this finding reports the first occurrence of a Malvaceae crop as a host for P. aegyptiaca. References: (1) H. Eizenberg et al. Weed Sci. 55:152, 2007. (2) M. Ghotbi et al. Int. J. Agri. Sci. 2:62, 2012. (3) G. V. G. Krishnamurthy et al. Indian J. Weed Sci. 9:95, 1977. (4) Y. Ma et al. Agron. J. 104:569, 2012.

First Report of Orobanche crenata Parasitism on Ornamental Anemone (Anemone coronaria) in Israel.

Broomrapes (Orobanche spp.) are obligatory parasitic weeds that infect roots of vegetables and field crops worldwide, resulting in severe damage. Orobanche crenata Forsk is common in agricultural fields in the Mediterranean Basin, Southern Europe, and the Middle East and is known as an important scourge of grain and forage legumes and of some Apiaceous crops such as carrot (Daucus carota L.) and celery (Apium graveolens L.) (3,4). To our knowledge, in this note, we report for the first time on Anemone coronaria L. (Ranunculaceae) as a new host for O. crenata and this is also the first report of Orobanche parasitism on a geophytic crop. Anemone (Anemone coronaria L.) is a high-value ornamental crop, which is commercially grown for cut flowers. Four anemone cultivars (Meron Red, Galil White, Jerusalem Blue, and Jerusalem Pink) were planted in September 2006 in a 2-ha field in Israel. The previous crop, broad bean (Vicia faba L.), was heavily infected during 2005 by O. crenata. In February 2007, O. crenata parasitized the anemone plants and developed numerous fertile flowering stalks throughout the field. The four anemone cultivars were equally infected by the parasite. Additional flowering stalks were still emerging on anemone plants during July 2007. Washing the root system clearly verified direct connection between the parasite and anemone roots. The parasite species was identified morphologically after Flora Europea (1) and Flora Palaestina (2). In addition, the stem had the fragrance typical of O. crenata. Neither symptoms nor visible qualitative or quantitative damage could be detected on infected anemone plants compared with noninfected plants. However, anemone appears to be an alternate host on which O. crenata can produce additional seed for the parasite seed bank. References: (1) A. O. Chater and D. A. Webb. Orobanche. Page 285 in: Flora Europaea. T. G. Tutin et al., eds. Vol. 3. University Press, Cambridge, 1972. (2) N. Feinbrun-Dothan. Page 210 in: Flora Palaestina. Vol. 3. Israel Academy of Sciences and Humanities, Jerusalem, 1978. (3) D. M. Joel et al. Hortic. Rev. 33:267, 2007. (4) C. Parker and C. R. Riches. Page 111 in: Parasitic Weeds of the World: Biology and Control. CAB International, Wallingford, Great Britain, 1993.

A new method for in-situ monitoring of the underground development of Orobanche cumana in sunflower (Helianthus annuus) with a mini-rhizotron.

AIMS: To develop an in-situ, non-destructive method for observation and monitoring of the underground developmental stages of the root parasite Orobanche cumana. SCOPE: The parasitic weed Orobanche causes severe damage to vegetables and field crops. Most of the damage caused to the crops occurs during the underground, unobservable parasitism stage. Sunflower (Helianthus annuus 'Adi') plants were planted in soil that was artificially inoculated with O. cumana seeds. Clear Plexiglas mini-rhizotron plastic observation tubes were inserted into the soil. Seed germination, early stage of penetration, and formation of tubercles and spikes were observed non-destructively and were monitored throughout the growing season by mean of a mini-rhizotron camera. Use of this technology enabled the complete individual parasite life cycle from the very early development (including germination) to Orobanche shoot to be monitored. In addition, the effect of the systemic herbicide Cadre (imazapic) on the development of O. cumana was inspected and quantified. CONCLUSIONS: This novel methodology facilitates the in-situ study of major aspects of the host-parasite interaction and of parasite suppression, such as parasitism dynamics, parasite growth rate, and the effect of chemical treatments on the parasite.

First Report of a New Race of Sunflower Broomrape (Orobanche cumana) in Israel.

The genus Orobanche includes chlorophyll-lacking root parasites that parasitize many dicotyledonous species and causes severe damage to vegetable and field crops worldwide. Sunflower broomrape (Orobanche cumana Wallr.) is known in Eurasia as a specific parasite of sunflower, which differs from the nodding broomrape (O. cernua Loefl) in host specificity and morphological characteristics (3). Together with Egyptian broomrape (O. aegyptiaca Pers.), it seriously parasitizes sunflower (Helianthus annuus L.) in Israel (1). Prior to 2000, the local confectionary sunflower cvs. Ambar and Gitit proved to be resistant to the local O. cumana populations in Israel (2). A preliminary study, which we conducted in 1995 using the Vranceanu's differentials (4), indicated that O. cumana populations in Israel behave like the known race C. Using random amplified polymorphic DNA analysis, we also found a very low intraspecific diversity of this species in Israel at that time. However, in 2000, infection of the sunflower cvs. Ambar and Gitit was reported in two fields (Gadot and Afek) in northern Israel. In 2001 and 2002, O. cumana parasitized these cultivars in three more locations as much as 50 km apart (Tel-Adashim, Mevo-Hama, and Bet-Hilel). To determine the virulence of O. cumana populations on sunflower cultivars under controlled conditions, O. cumana seeds were collected in the above mentioned sunflower fields. In addition, we also used seeds from an O. cumana population collected in Alonim in 1997. This latter population did not infect the above mentioned 'resistant' sunflower cultivars in the field (2,); therefore, represented the previously known O. cumana populations in Israel. Resistant (Ambar) and susceptible (D.Y.3) sunflower cultivars were planted in separate pots that were differentially filled with soil that was inoculated with O. cumana seeds of the different populations. The experiment was performed in a full factorial arrangement with six replications. As expected, O. cumana from Alonim failed to attack the resistant sunflower. However, the O. cumana populations that were collected in the five other fields seriously attacked both sunflower cultivars, indicating higher virulence. O. cumana from all five new populations proved more virulent than the Alonim population on cvs. Ambar and D.Y.3. The occurrence of these new virulent populations could have several reasons including: (i) importation of virulent parasite seeds from abroad; or (ii) local development of virulence from previously avirulent populations. The latter could be favored by the continuous and repeated use of the available resistant varieties that are all based on a single resistance response (2). References: (1) H. Eizenberg and D. M. Joel. Orobanche in Israeli agriculture. Workshop of COST Action 849, Parasitic Plant Management in Sustainable Agriculture, 2001. (2) H. Eizenberg et al. Plant Dis. 88:479, 2003. (3) D. M. Joel. Phytoparasitica 16:375, 1988. (4) A. V. Vranceanu et al. Proc. 9th Sunflower Conf. 1:74-82, 1980.

Variation in Responses of Sunflower Cultivars to the Parasitic Weed Broomrape.

Development of four Orobanche species, O. cumana, O. aegyptiaca, O. ramosa, and O. cernua, was compared on resistant and susceptible sunflower cultivars. Sunflower plants were infected by O. cumana, O. aegyptiaca, and O. ramosa, but not by O. cernua, in field and greenhouse studies. However, cultivating the hosts and parasites in a polyethylene bag system allowed the observation that sunflower induced O. cernua seed germination. This difference demonstrates that O. cernua is unique from the other three species. O. cumana, O. aegyptiaca, and O. ramosa attached to and developed tubercles on the susceptible sunflower 'Adi.' On the resistant 'Ambar' sunflower, a greater percentage of tubercles were degenerated or dead than on the susceptible cultivar. Thus, resistance of Ambar appears to manifest during tubercle development. Seed production of Adi sunflower was greatly reduced with infection by O. cumana.

Resistance to broomrape (Orobanche spp.) in sunflower (Helianthus annuus L.) is temperature dependent.

The effects of various temperature regimes in the range 29-17/21-9 degrees C day/night on each stage of the parasitism process of Orobanche cumana and O. aegyptiaca on sunflower were studied under controlled conditions in polyethylene bags. The response of the resistant sunflower variety 'Ambar' was expressed as the degeneration of the parasite tissues after its establishment in the plant roots, and this stage was found to be temperature dependent. The degeneration rate of Orobanche tubercles in the resistant sunflower variety was also found to be temperature dependent and was about five times as great as that in the sensitive variety in the highest temperature regime tested of 29/21 degrees C day/night. The ability to reject the parasite by causing its degeneration and death is the main factor that determines the resistance. As the temperature rises, more tubercles degenerate and die, that is the sunflower plant expresses higher levels of resistance.

First Report of the Parasitic Plant Orobanche aegyptiaca Infecting Olive.

Broomrapes (Orobanche spp.) are obligatory parasitic plants that infect the root system of vegetables and field crops worldwide resulting in severe damage. Five broomrape species are known as significant parasites of crops in Israel: O. aegyptiaca Pers., O. cernua Loefl., O. cumana Wallr., O. crenata Forssk., and O. ramose L. (1,2). Recently, O. aegyptiaca was found to parasitize roots of young olive trees (Olea europaea) in a 1-year-old plantation located in Esdraelon Valley, Israel (voucher specimens deposited in Newe-Ya'ar Weed Herbarium, Ramat Yishay, Israel). To our knowledge, this is the first time that a tree in general and olive in particular has been reported to serve as host for O. aegyptiaca. Washing the root system clearly verified connections between the parasite and olive roots. Cross sections of an attachment site confirmed the development of functional haustoria. Trees were planted in a field where tomatoes had been previously parasitized by O. aegyptiaca for several years. In April 2001, many O. aegyptiaca plants emerged under each olive tree in a total area of 0.3 ha. Additional emergence of O. aegyptiaca was observed until July 2001. The high level of Orobanche infection did not lead to visible damage in the trees. However, the mature parasite developed massive amounts of seeds, serving to increase the population of O. aegyptiaca in the field. References: (1) D. M. Joel and H. Eizenberg. Three Orobanche species newly found on crops in Israel. Phytoparasitica 30:187, 2002. (2) C. Parker and C. R. Riches. Parasitic Weeds of the World. CAB International, Wallingford, UK, 1993.