The results demonstrate considerable efficacy of natural phytoecdysteroids against major agricultural pests, and suggests that these materials should be considered for potential development of friendly control agents.

No abstract

RNA silencing refers to diverse mechanisms that control gene expression at transcriptional and post-transcriptional levels which can also be used in parasitic pathogens of plants that Broomrapes (Orobanche/Phelipanche spp.) are holoparasitic plants that subsist on the roots of a variety of agricultural crops and cause severe negative effects on the yield and yield quality of those crops. Effective methods for controlling parasitic weeds are scarce, with only a few known cases of genetic resistance. In the current study, we suggest an improved strategy for the control of parasitic weeds based on trans-specific gene-silencing of three parasite genes at once. We used two strategies to express dsRNA containing selected sequences of three Phelipanche aegyptiaca genes PaACS, PaM6PR, and PaPrx1 (pma): transient expression using Tobacco rattle virus (TRV:pma) as a virus-induced gene-silencing vector and stable expression in transgenic tomato Solanum lycopersicum (Mill.) plants harboring a hairpin construct (pBINPLUS35:pma). siRNA-mediated transgene-silencing (20–24 nt) was detected in the host plants. Our results demonstrate that the quantities of PaACS and PaM6PR transcripts from P. aegyptiaca tubercles grown on transgenic tomato or on TRV-infected Nicotiana benthamiana plants were significantly reduced. However, only partial reductions in the quantity of PaPrx1 transcripts were observed in the parasite tubercles grown on tomato and on N. benthamiana plants. Concomitant with the suppression of the target genes, there were significant decreases in the number and weight of the parasite tubercles that grew on the host plants, in both the transient and the stable experimental systems. The results of the work carried out using both strategies point to the movement of mobile exogenous siRNA from the host to the parasite, leading to the impaired expression of essential parasite target genes.

Many species of the genus Ajuga (family Lamiaceae) contain phytoecdysteroids and clerodane diterpenes. Phytoecdysteroids are triterpene-derived analogues of steroid hormones that control molting and metamorphosis in arthropods, whereas clerodanes deter phytophagous insects. We identified and quantified phytoecdysteroid and clerodane contents in three Ajuga plant species in Israel. Leaves and roots of Ajuga iva, Ajuga chamaepitys (Ajuga chia), and Ajuga orientalis were collected from three different populations. Using liquid chromatography–time of flight–mass spectrometry analysis, we identified three phytoecdysteroids: 20-hydroxyecdysone (ecdysterone), makisterone A, and cyasterone and two clerodanes: dihydroajugapitin and columbin. Their contents varied significantly among plant species, organs, and populations. The highest concentrations of 20-hydroxyecdysone, makisterone A, and cyasterone were recorded in leaves and roots of A. iva. Cyasterone content tended to be higher in leaves of A. chamaepitys. Clerodane concentrations were generally negligible or nonexistent. Dihydroajugapitin concentrations were highest in A. iva leaves but were lower or undetectable in the roots and in the other two species. Columbin concentration was similar in all species and organs. Phytoecdysteroid contents also varied among populations within species. Because phytoecdysteroids have disruptive effects on phytophagous insect growth, the potential role of extracts of A. iva in pest-management programs is of interest.

Solanum rostratum Dunal is an invasive weed species that invaded Israel in the 1950s. The weed appears in several germination flashes, from early spring until late summer. Recently, an increase in its distribution range was observed, alongside the identification of new populations in the northern part of Israel. This study aimed to investigate the efficacy of herbicide application for the control of S. rostratum using two field populations originated from the Golan Heights and the Jezreel Valley. While minor differences in herbicide efficacy were recorded between populations, plant growth stage had a significant effect on herbicide response. Carfentrazone-ethyl was found to be highly effective in controlling plants at both early and late growth stages. Metribuzin, oxadiazon, oxyfluorfen and tembutrione showed reduced efficacy when applied at later growth stage (8–9 cm height), as compared to the application at an early growth stage (4–5 cm height). Tank mixes of oxadiazon and oxyfluorfen with different concentrations of surfactant improved later growth stage plant control. Taken together, our study highlights several herbicides that can improve weed control and may be used as chemical solutions alongside diversified crop rotation options. Thus, they may aid in preventing the spread and further buildup of S. rostratum field populations.