Relationships between Agronomic Practices, Soil Chemical Characteristics and Striga Reproduction in Dryland Areas of Tanzania

The parasitic weed Striga poses a serious threat to cereal production in sub-Saharan Africa. For many years, technological packages for the control of this weed were proposed and implemented on farmers＇ fields. A survey was carried out in farmers＇ fields in 2010/201l cropping season in selected dryland areas of Tanzania to： （a） determine the Striga plant counts, number of capsules/Striga plant and agronomic practices used by farmers to control Striga; and （b） evaluate the relationship between Striga reproduction, soil chemical characteristics and agronomic practices. Soil samples at 0-20 cm depth were collected from 20 different farmers＇ fields. The soil samples were analyzed for pH, organic carbon, N, P and K. Results showed that there was low adoption of recommended Striga control methods. Regression analysis of agronomic practices and soil chemical characteristics revealed a positive improvement of soil N and organic carbon and reduction of soil P and K content as one shifted from sole planting to intercropping. The results showed that potassium was highly positively related to number of capsules/Striga plant. There was a reduction in the number of capsules/plant as one moved from sole planting to intercropping. Based on these findings, K in the Striga infested in soils positively influenced Striga reproduction and seed bank replenishment, hence high soil K levels may lead to high Striga incidence.

Alectra vogelii: A Threat to Bambara Groundnut Production under Climate Change: A Review Paper

Bambara groundnut (BGN) is a protein-rich pulse with the ability to lead to more climate-resilient agriculture. The objective of this study was to review Alectra vogelii as a potential threat to BGN production as a result of climate change. However, the crop faces biotic and abiotic stresses. Alectra vogelii is a major biotic constraint to BGN production, especially in Africa’s non-fertile semi-arid regions. Alectra vogelii (L.) Benth is a parasitic weed in the Orobanchaceae family that causes major damage by forming haustoria attached to roots to enable absorption of nutrients from the BGN. Alectra vogelii produces a large number of minute seeds that can live in the soil for up to 20 years. Based on the reviewed literature, various control mechanisms for dealing with the harmful effects of Alectra vogelii have been proposed. The aim of this research was to reveal the effect of Alectra vogelii on BGN and possible control strategies. We discuss the different control methods such as cultural and mechanical management procedures, phosphorus fertilizers and resistant host crops, herbicide use, and integrated Alectra vogelii control methods. In adaptive methods, however, new techniques remain important. The life cycle of root parasitic weeds is inextricably linked to that of their host, making it an ideal target for such new control techniques, especially when aimed at the early stages of the host-parasite relationship. This review reveals additional information on the function of parasitic seed, strigolactones and how they can be used in breeding to management parasitic weeds.

On improving strigolactone mimics for induction of suicidal germination of the root parasitic plant Striga hermonthica

Strigolactones(SLs)are plant hormones that regulate the branching of plants and seed germination stimulants of root parasitic plants.As root parasites are a great threat to agricultural production,the use of SL agonists could be anticipated to provide an efficient method for regulating root parasites as suicidal germination inducers.A series of phenoxyfuranone-type SL mimics,termed debranones,has been reported to show potent bioactivities,including reduction of the tiller number on rice,and stimulation of seed germination in the root parasite Striga hermonthica.To exert both activities,two substituents on the phenyl ring of the molecules were important but at least a substituent at the 2-position must be an electron-withdrawing group.However,little is known about the effect of the properties of the substituents at the 2-position on bioactivities.Here,we found that different substituents at the 2-position give different preferences for bioactivities.Halogenated debranones were more effective than the others and SL agonist GR24 for inhibiting rice tiller but far less effective in the induction of S.hermonthica germination.Meanwhile,nitrile and methyl derivatives clearly stimulated the germination of S.hermonthica seeds.Although their IC_(50) values were 100 times higher than that of GR24 in the receptor competitive binding assay,their physiological activities were approximately 1/10 of GR24.These differences could be due to their uptake in plants and/or their physicochemical stability under our experimental conditions.These findings could support the design of more potent and selective SL agonists that could contribute to solving big agricultural issues.

Strigolactone Analogs as Molecular Probes in Chasing the （SLs） Receptor/s： Design and Synthesis of Fluorescent Labeled Molecules

Originally identified as allelochemicals involved in plant-parasite interactions, more recently, Strigolactones （SLs） have been shown to play multiple key roles in the rhizosphere communication between plants and mycorrhizal fungi. Even more recent is the hormonal role ascribed to SLs which broadens the biological impact of these relatively simple molecules. In spite of the crucial and multifaceted biological role of SLs, there are no data on the receptor（s） which bind（s） such active molecules, neither in the producing plants nor in parasitic weeds or AM fungi. Information about the putative receptor of SLs can be gathered by means of structural, molecular, and genetic approaches. Our contribution on this topic is the design and synthesis of fluorescent labeled SL analogs to be used as probes for the detection in vivo of the receptor（s）. Knowledge of the putative receptor structure will boost the research on analogs of the natural substrates as required for agricultural applications.

A Fluorescent Alternative to the Synthetic Strigolactone GR24

Strigolactones have recently been implicated in both above- and below-ground developmental pathways in higher plants. To facilitate the molecular and chemical properties of strigolactones in vitro and in vivo, we have devel- oped a fluorescent strigolactone molecule, CISA-1, synthesized via a novel method which was robust, high-yielding, and used simple starting materials. We demonstrate that CISA-1 has a broad range of known strigolactone activities and further report on an adventitious rooting assay in Arabidopsis which is a highly sensitive and rapid method for testing biological activity of strigolactone analogs. In this rooting assay and the widely used Orobanche germination assay, CISA-1 showed stronger biological activity than the commonly tested GR24. CISA-1 and GR24 were equally effective at inhibiting branching in Arabidopsis inflorescence stems. In both the branching and adventitious rooting assay, we also demonstrated that CISA-1 activity is dependent on the max strigolactone signaling pathway. In water methanol solu- tions, CISA-1 was about threefold more stable than GR24, which may contribute to the increased activity observed in the various biological tests.