Striga hermonthica is one of the most important parasitic weeds affecting sorghum productivity in sub-Saharan African regions, characterized by dry and harsh environmental conditions 10. Nutrients depletion in the soil were noticed as the major constraints limiting sorghum cultivation 17 and the expected grain yield 4. Thus, in some African countries, affected by poverty and low soil fertility farmers are not able to increase productivity of sorghum because of limited resources 3. The lack of nutrients in the soil predispose plants to diseases and also to Striga, which seriously affects sorghum productivity in sub-Saharan African region with yield losses of between 20 to 80% 20.

In fact, there is a high correlation between soil fertility decline and the negative impact of Striga. Thus,

when there are sufficient nutrients like nitrogen in the soil it will reduce strigolactone production from the host plant and vice versa 9. Otherwise nitrogen presence in the soil considerably increase yield and reduce the impact of Striga 18. Nutrient deficiency in the soil highly affect organic matter and biomass production 15. In addition, phosphate utilization also has the ability to decrease strigolactone secretion and reduce Striga germination 7.

Fertilizer application can produce vigorous plants that smother the weed and improve sorghum yield 16. Striga seed germination is an important step in the infection process between sorghum plants root and Striga root. The germination is conditioned by the presence of molecular signals from the host plants. Those signals are called strigolactone and are produced by an arbuscular mycorrhizal (AM) fungi through symbiotic interactions in the rhizosphere. When there is a lack of nutrients in the soil, strigolactone hormones are produced by the host plant for nutrients acquisition 6. Fertilizer application that contains nitrogen and phosphorous can reduce Striga incidence through low strigolactone secretion in the soil 13.

In African countries, the inputs are greater than the outputs in terms of nutrients utilizations and are considerably affecting the yield 19. Poverty, globalization, soil infertility coupled with the impact of Striga, has necessitated the investigation of fertilizer micro dosing application at very low levels for better grain yield. In Niger, in order to control the weed and to regenerate soil fertility, farmers are using Nere powder (Parkia biglobosa), fertilizers (NPK 15-15-15, Urea, DAP) and sesame seed. As the most accessible crop utilized by farmers’ to fight the weed in Niger, sesame is a drought tolerant crop which give more benefit for less cost than the other crops. In Niger, it is cultivated in divers’ agro ecological areas as a cash crops 2. For many years’ suicidal germination has been also promoted as a powerful technique for reducing Striga seed in the soil using sesame seed or cowpea. This Integrated Striga management (ISM) allows smothering of Striga plant after the germination process 14.

The high prices of fertilizers and manure inaccessibility are pushing the smallholder farmers to re-orient

their energies on traditional management methods to reduce Striga incidence and increase sorghum grain yield.

The main objective of this study was to assess the effectiveness of three doses of sesame (0, 0.5 and 1.5 g) and DAP (0, 2 and 5 g) on Striga impact and sorghum grain yield.

Sorghum and Striga seeds materials: This study involved twenty (20) sorghum varieties from diversified countries and landraces from Niger (Table 1). From the 20 varieties, 15 are documented Striga resistant lines and the five 5 others lines are Niger susceptible landraces highly preferred by famers in Tahoua and Maradi regions.

The Striga hermonthica seeds for the field experiment were collected in November 2016 in Tahoua region, in highly infested farmers’ sorghum fields. Thereafter the Striga plants were dried and seed extracted.

The extracted seeds were stored in bottles at 25 °C for use at Konni station in the Konni seed laboratory.

The study was conducted in Konni station located around 5 km to Konni (Latitude: 13 48' 00'' Longitude: 5 15' 00'') a department of Tahoua region. It is located about 417 Km from Niamey the capital. In this area, the rainfall is around 500 to 600 mm per year. Konni is an important area devoted to agriculture (INS, 2017). It is a center of excellence of diverse sorghum varieties cultivation. However, the area is highly infested by the weed and an ideal site for field screening and sorghum cultivation. Thus, Konni is identified as one the most important sorghum producing places in Niger. Konni station is the only research center of INRAN Niger authorized to undergo Striga field screening activities with experienced technicians. Since 1990, several field screening activities were elaborated by diverse projects based on Striga management 21.

SAS 9.4 software was used in a general linear model (GLM) for ANOVA of the different variables scored. Correlation was also determined to establish the relationships among the traits. Before the analysis a test for normality was performed using GenStat 15th Edition (2007).

Nitrogen deficiency and phosphorous depletion in the soil were reported by many researchers to be involved in the increases of Striga hermonthica impact in sorghum cultivation in sub-Saharan African regions 1.

In this experiment characterized by the utilization of three different doses of DAP and sesame seeds utilization respectively at 0, 2, 5 g and 0, 0.5, 1.5 g on Striga emerged plants number and sorghum plant growing parameters. Thus, those parameters include the plant vigor, the Striga emergence, the number of Striga plants that have emerged at 45, 60, 90 days after sorghum sowing date, and the grain yield. The assessment also concerned the interaction effect of DAP and sesame. The different results obtained on each treatment gave more information on the impact of the different doses effect used in the study. Therefore, the DAP was highly significant on the plant vigor. Between the three level of DAP use, the dose one of DAP (2g) have positively impact the plant vigor. Concerning the Striga emergence, no significant impact was observed from the sesame seeds doses. Thus, for the DAP application at different doses on the Striga emergence, moderate effect was observed with the dose two of DAP. For the interaction several combinations have performed well for Striga emerged plant number reduction, it concerns the combination one (T1), two (T2), seven (T7), five (T5) and three (T3). Between the cited combinations, the number one and two are the best response in terms of less emerged Striga plants. The different effect of the DAP fertilizer and the sesame seed have consistent effect on the plant vigor and the Striga emergence. The number of emerged Striga plants at 45, 60 and 90 days were also highly impacted by the different combinations in this study, confirmed by the study made Jamil 2012. Thus, the DAP fertilizer micro dose level one (2g) performed well by decreasing the Striga plant numbers in the different plots at 45, 60 and 90 days as mentioned by Jamil 2012 where it reduced Striga plant number from 66 to 70%. The sesame level two (1.5 g) well performed on the Striga plants number reduction at 45, 60, 90 days. Concerning the interaction impact, according to the different parameters the responses were different. Therefore, for the number of Striga plants at 45 days after sowing, the combination one, two, three, four, five, seven gave less Striga plants compared to the other combinations. Among those treatment, the number one, four, seven were the best treatment which highly reduced Striga plants number at the 45 days. Thus, concerning the entries responses at 45, 60 and 90 days after sowing there were nine genotypes which performed well by showing less Striga plants around, those genotypes are the genotype 3 (P9401), the genotype 4 (P9403), the genotype 5 (Brahan), the genotype 6 (S35), the genotype 7 (F2-20), the genotype 8 (CE 150-262), the genotype 9(04CZ-F5P-52), the genotype 10 (ICS1049), the genotype 13 (P9406), the genotype 14 (P9405) and the genotype 16 (TXN13 BC3F5-41).

Those genotypes are documented Striga resistant sorghum genotypes from diverse countries 58. This confirmed the fact that there are Striga resistant varieties despite the aggressiveness of the Striga hermonthica found in Niger. For the grain yield, the sesame seed effect was not significant. That means, it does not affect the yield of the twenty genotypes used in the experiment.

Concerning the DAP, it is highly effective on the grain yield with the level 2. The results confirm the previous studies made by Jamil 2010, where they have mentioned that West African country soil are characterized by less nitrogen and phosphorous, and the effectiveness of DAP micro dosing utilization can increase the yield with different level of micro dosing. Thus, according to the country and the type soil we are dealing with, the DAP quantity for the grain yield and the Striga management should be different. The interaction sesame and DAP also performed well on the grain yield with the treatment one and the treatment eight.

DAP utilization at the level one micro dosing (2 g) highly reduced Striga emergence and plant number distribution in sorghum cultivation. Concerning the sesame seed, effective responses were also observed on Striga related parameters with the level two micro dosing (1.5g) by reducing striga effect. In this study, the combination sesame seed, and DAP significantly reduced the negative impact of Striga on sorghum plants and increased sorghum grain yield.