Striga seed-germination activity of root exudates and compounds present in stems of Striga host and nonhost (trap crop) plants is reduced due to root colonization by arbuscular mycorrhizal fungi.

Root colonization by arbuscular mycorrhizal (AM) fungi reduces stimulation of seed germination of the plant parasite Striga (Orobanchaceae). This reduction can affect not only host plants for Striga, resulting in a lower parasite incidence, but also false hosts or trap crops, which induce suicidal Striga seed germination, thereby diminishing their effectiveness. In order to better understand these AM-induced effects, we tested the influence of root colonization by different AM fungi on the seed-germination activity of root exudates of the Striga hermonthica nonhost plants cowpea and cotton on S. hermonthica. We also tested the effect of AM fungi on the seed-germination activity of the Striga gesnerioides host plant cowpea on S. gesnerioides. Moreover, we studied whether mycorrhization affects the transport of seed-germination activity to above-ground plant parts. Mycorrhization not only resulted in a lower seed germination of S. gesnerioides in the presence of root exudates of the S. gesnerioides host cowpea but also seed germination of S. hermonthica was also lower in the presence of root exudates of the S. hermonthica nonhosts cowpea and cotton. Downregulation of the Striga seed-germination activity occurs not only in root exudates upon root colonization by different AM fungi but also in the compounds produced by stems. The lowered seed-germination activity does not appear to depend on the presence of seed germination inhibitors in the root exudates of mycorrhizal plants. The implication for Striga control in the field is discusse

A Review on: The Effect of Agro Forestry Trees on Minimizing Infestation of Striga hermonthica Through the Enhancement of Arbuscular mycorrhiza (AM) with Sorghum in the Northern Part of Ethiopia

Sorghum is one of the major food grain crops in Ethiopia, especially in the northern part of the country. The production and productivity of sorghum is affected by the root hemi parasite Striga hermonthica (Del.) Benth. (Orobanchaceae). In Ethiopia it is limited integrated control measure have been carried out to combat Striga. Reasons for the limited success in Striga control include prolific seed production, monocropping, close coupling of its life cycle to that of its host, and the fact that effective control methods are not within the reach of farmers practicing subsistence agriculture (Oswald A.2005). Sustainable management systems targeting Striga management on cereals in general or sorghum in particular might benefit from managing this symbiotic interaction. Agro forestry trees have the capacity to enhance AM and symbiotic relationship between sorghum can blocks for Striga hermonthica so as not to get any communication with its host. Keywords: AM symbiotic, Striga hermonthica

Stacking tolerance to drought and resistance to a parasitic weed in tropical hybrid maize for enhancing resilience to stress combinations

Open Access JournalMaize is a food security crop cultivated in the African savannas that are vulnerable to the occurrence of drought stress and Striga hermonthica infestation. The co-occurrence of these stresses can severely damage crop growth and productivity of maize. Until recently, maize breeding in International Institute of Tropical Agriculture (IITA) has focused on the development of either drought tolerant or S. hermonthica resistant germplasm using independent screening protocols. The present study was therefore conducted to examine the extent to which maize hybrids simultaneously expressing resistance to S. hermonthica and tolerance to drought (DTSTR) could be developed through sequential selection of parental lines using the two screening protocols. Regional trials involving 77 DTSTR and 22 commercial benchmark hybrids (STR and non-DTSTR) were then conducted under Striga-infested and non-infested conditions, managed drought stress and fully irrigated conditions as well as in multiple rainfed environments for 5 years. The observed yield reductions of 61% under managed drought stress and 23% under Striga-infestation created desirable stress levels leading to the detection of significant differences in grain yield among hybrids at individual stress and non-stress conditions. On average, the DTSTR hybrids out-yielded the STR and non-DTSTR commercial hybrids by 13–19% under managed drought stress and fully irrigated conditions and by −4 to 70% under Striga-infested and non-infested conditions. Among the DTSTR hybrids included in the regional trials, 33 were high yielders with better adaptability across environments under all stressful and non-stressful testing conditions. Twenty-four of the 33 DTSTR hybrids also yielded well across diverse rainfed environments. The genetic correlations of grain yield under managed drought stress with yield under Striga-infestation and multiple rainfed environments were 0.51 and 0.57, respectively. Also, a genetic correlation between yields under Striga-infestation with that recorded in multiple rainfed environments was 0.58. These results suggest that the sequential selection scheme offers an opportunity to accumulate desirable stress-related traits in parents contributing to superior agronomic performance in hybrids across stressful and diverse rainfed field environments that are commonly encountered in the tropical savannas of Africa

Cloning and characterisation of a maize carotenoid cleavage dioxygenase (ZmCCD1) and its involvement in the biosynthesis of apocarotenoids with various roles in mutualistic and parasitic interactions

Colonisation of maize roots by arbuscular mycorrhizal (AM) fungi leads to the accumulation of apocarotenoids (cyclohexenone and mycorradicin derivatives). Other root apocarotenoids (strigolactones) are involved in signalling during early steps of the AM symbiosis but also in stimulation of germination of parasitic plant seeds. Both apocarotenoid classes are predicted to originate from cleavage of a carotenoid substrate by a carotenoid cleavage dioxygenase (CCD), but the precursors and cleavage enzymes are unknown. A Zea mays CCD (ZmCCD1) was cloned by RT-PCR and characterised by expression in carotenoid accumulating E. coli strains and analysis of cleavage products using GC¿MS. ZmCCD1 efficiently cleaves carotenoids at the 9, 10 position and displays 78% amino acid identity to Arabidopsis thaliana CCD1 having similar properties. ZmCCD1 transcript levels were shown to be elevated upon root colonisation by AM fungi. Mycorrhization led to a decrease in seed germination of the parasitic plant Striga hermonthica as examined in a bioassay. ZmCCD1 is proposed to be involved in cyclohexenone and mycorradicin formation in mycorrhizal maize roots but not in strigolactone formatio

LONG-RUN STRIGA CONTROL BY SUBSISTENCE FARMERS IN MALI

A dynamic programming model is developed to identify barriers to the adoption of long-run control programs for the parasitic weed Striga. The model is applied to Sirakorola in northwestern Mali. The ability of national and village-level institutions to overcome the barriers to adoption is explored.Community/Rural/Urban Development, Research and Development/Tech Change/Emerging Technologies,

Genetic diversity and population structure of Striga hermonthica populations from Kenya and Nigeria

Article purchasedStriga hermonthica is a parasitic weed that poses a serious threat to the production of economically important cereals in sub-Saharan Africa. The existence of genetic diversity within and between S. hermonthica populations presents a challenge to the successful development and deployment of effective control technologies against this parasitic weed. Understanding the extent of diversity between S. hermonthica populations will facilitate the design and deployment of effective control technologies against the parasite. In the present study, S. hermonthica plants collected from different locations and host crops in Kenya and Nigeria were genotyped using single nucleotide polymorphisms. Statistically significant genetic differentiation (FST = 0.15, P = 0.001) was uncovered between populations collected from the two countries. Also, the populations collected in Nigeria formed three distinct subgroups. Unique loci undergoing selection were observed between the Kenyan and Nigerian populations and among the three subgroups found in Nigeria. Striga hermonthica populations parasitising rice in Kenya appeared to be genetically distinct from those parasitising maize and sorghum. The presence of distinct populations in East and West Africa and in different regions in Nigeria highlights the importance of developing and testing Striga control technologies in multiple locations, including locations representing the geographic regions in Nigeria where genetically distinct subpopulations of the parasite were found. Efforts should also be made to develop relevant control technologies for areas infested with ‘rice-specific’ Striga spp. populations in Kenya

Assessment of Striga hermonthica infestation and effectiveness of current management strategies in maize-based cropping systems in eastern Uganda

Striga is a major constraint to cereal production in the tropics, particularly on soils of low fertility. Striga causes 30 to 80% cereal crop losses in sub-Saharan Africa. The objective of this study was to assess farmers’ perception of level of infestation and efficacy of current management options of Striga (Striga hermonthica (Delile) Benth) in maize-based cropping systems in eastern Uganda. A survey was conducted in Iganga district in eastern Uganda, involving 360 households. On the basis of the survey outputs, on-farm trials were conducted to assess the efficacy of a herbicide seed-coating technology, imazapyr herbicide resistant maize (IR-maize) variety, either as a sole crop or intercropped with soybean (Glycine max) or common beans (Phaseolus vulgaris L). The study revealed that S. hermonthica caused more than 50% maize (Zea mays) yield loss and farmers were dissatisfied with the existing control practices. Farmers’ knowledge about Striga was mainly sourced from agricultural extension service providers. The on-farm trials revealed that IR-maize provided effective protection against S. hermonthica infestation. Also, intercropping Longe 6H maize variety with either soybean or common beans significantly reduced Striga infestation in farmers’ fields. Longe 6H-soybean intercropping reduced Striga infestation by 32%; while Longe 6H-common bean intercropping reduced Striga infestation by 14%. Intercropping either IR-maize or Longe 6H hybrid (farmer-preferred) with the aforementioned legumes, reduced S. hermonthica infestation (30–50%) and improved maize yield parameters (20-30%). For effective management of S. hermonthica in the maize-based cropping systems in eastern Uganda, farmers should be encouraged to adopt the improved IR-maize and intercrop farmer-preferred maize varieties with legumes in order to improve maize yields

Potential Markets for Herbicide Resistant Maize Seed for Striga Control in Africa

Striga is an obligate parasitic weed attacking cereal crops in Subsaharan Africa. In Western Kenya, it is identified by farmers as their major pest problem in maize. A new technology, consisting of seed coating of herbicide tolerant maize varieties, has prove to be very effective in farmer fields. To bring this technology to the farmer, a sustainable delivery system needs to be developed, preferably through the private sector. To help of the seed companies develop a strategy, the potential market for this technology is hereby calculated, combines different data sources into a Geographic Information System (GIS). Superimposing secondary data, field surveys, agricultural statistics and farmer surveys makes it possible to clearly identify the Striga-prone areas in western Kenya. According to the analysis, the area has 212,000 ha in maize annually, with a population of 5.9 million people and a maize production of 480,000 kg, or 81 kg/person. Population density is high at 359 people/km2. A farmer survey reveals that 70% of farmers in this zone have Striga in their fields. Contingent valuation methods indicate that farmers' would be willing to buy on average 3.67 kg of the new seed each. This translates into a potential demand of 3,400 to 5,200 tons annually. Similar calculations, but based on much less precise data and expert opinion, not farmer surveys, estimate the potential market for herbicide tolerant maize against Striga at 64,600 tons annually, with an estimated value of $129 million.maize, Striga, Africa, weeds, pest control, Crop Production/Industries, Q12,

Occurrence and growth inhibitory activity of Striga hermonthica (delile) benth on Sorghum bicolor (L.) moench in Lafia, Nigeria

Incidence of Striga hermonthica was investigated on some Sorghum bicolor farms in Lafia, Nigeria. Quadrant sampling technique was used and a total of six plots of size 10m x 10m each were sampled randomly in three locations, namely; Shabu, Shendam Road and Makurdi Road in Lafia North, East and Central respectively. Incidence parameters such as the number of Striga and Sorghum, the height of Striga, distance of Striga to infected Sorghum and height of Sorghum were documented. A total of 572 stands of Striga were counted in all sampled locations. Sorghum farms in Shabu had the highest mean population of Striga (261), followed by both Shendam and Makurdi Road with mean populations of 13 Striga each. Negative correlations were observed between height of Striga and height of infected Sorghum (-0.371), as well as between number of Striga and number of Sorghum plants (-0.818). Distance of Striga to infected Sorghum correlated positively with height of infected Sorghum (0.153). Positive correlation was also observed between number of Striga and height of infected Sorghum (0.584). It was thus concluded that Striga had a significant negative effect on growth of Sorghum in the study area. Therefore this activity of Striga require integrated management approaches for sustainable Sorghum production and yield improvement.Keywords: Incidence, Lafia, Parasitic activity, Striga, Sorghu