Advanced Technologies for Parasitic Weed Control

Parasitic weeds such as Phelipanche and Orobanche are obligate holoparasites that attack roots of almost all economically important crops in semiarid regions of the world. A wide variety of parasitic weed control strategies (chemical, biological, cultural, and resistant crops) has been tried. Unfortunately, most are partially effective and have significant limitations. The current mini review will discuss the needs for alternative methods and will summarize current and new biotechnology-based approaches for broomrape control. At present, we have generated transgenic tobacco plants expressing a cecropin peptide (sarcotoxin IA), under the control of the inducible HMG2 promoter. Transgenic lines enhanced host resistance to the parasitic weed; transgenes showed higher numbers of aborted parasitization events, reduced Phelipanche biomass, and increased host biomass. Sarcotoxin IA had no obvious effect on growth and development of transgenic host plants. Mannitol content in the parasite is regulated by Mannose 6-Phosphate Reductase (M6PR) gene, an essential process to broomrape species for water and nutrient uptake from the host. In our study, we used the inverted repeat technique to silence the parasite target gene, M6PR. In this study it was shown that the endogenous M6PR mRNA from P. aegyptiaca tubercles or shoots grown on transgenic tomato plants harboring the M6PR silencing construct was reduced by 60 to 80%. The number of dead tubercles was also increased significantly on transgenic plants as compared with the control plants. The strategies presented here are potentially superior to other methods in that they are effective, have a low cost of implementation for producers, and are safe for the environment.

Induced Expression of Sarcotoxin IA Enhanced Host Resistance Against Both Bacterial and Fungal Pathogens in Transgenic Tobacco

We demonstrate here that induced expression of sarcotoxin IA, a bactericidal peptide from Sarcophaga peregrina, enhanced the resistance of transgenic tobacco plants to both bacterial and fungal pathogens. The peptide was produced with a modified PR1a promoter, which is further activated by salicylic acid treatment and necrotic lesion formation by pathogen infection. Host resistance to infection of bacteria Erwinia carotovora subsp. carotovora and Pseudomonas syringae pv. tabaci was shown to be dependent on the amounts of sarcotoxin IA expressed. Since we found antifungal activity of the peptide in vitro, transgenic seedlings were also inoculated with fungal pathogens Rhizoctonia solani and Pythium aphanidermatum. Transgenic plants expressing higher levels of sarcotoxin were able to withstand fungal infection and remained healthy even after 4 weeks, while control plants were dead by fungal infection after 2 weeks.