Striga Aspera Research Articles

Striga aspera (witchweed)

Striga aspera (witchweed)

Striga (Witchweed) Threats to Cereal Crops Production and Its Management: A Review

Striga (witchweed) is one of the most successful parasitic weeds of cereal crops in Africa. It is ‘a poor farmer’s problem’ as there is a near perfect ecological overlap between areas of Striga infestation and where hunger prevails. It is originated in Semien hills of Ethiopia and the Nubian hills of Sudan and later expanded in about 42 African countries. Striga hermonthica, Striga asiatica, Striga gesnerioides, and Striga aspera constitute the greatest economic threat to cereal crops’ yield losses. They are obligate root parasites causing growth inhibition and yield losses of 20-100% in maize, rice, sorghum, pearl millet, finger millet, sugar cane and cowpea. Cultural practices such as long-term rotational cultivation of cereal crops with legume crops unaffected by the parasite is effective in managing the weed. Besides, biological control by use of parasitic fungi ( Fusarium oxysporum and Vesicular arbuscular mycorrhiza) play a role in managing the weed. In addition, chemical control with imidazolinone herbicide, ethylene gas, dicamba and 2,4-D are effective in managing striga in cereal crops in extreme cases. Integrated use of striga resistant crop varieties with water conservation practices, soil fertility amendment and use of parasitic fungi ( Fusarium oxysporum and Vesicular arbuscular mycorrhiza) is effective in control, economically safe, socially acceptable and environmentally friendly than a single control measure. Therefore, the promising integrated striga management practices should be highly promoted. Moreover, host and Striga species specific integrated Striga management should be designed. Keywords: Haustoria; Obligate parasite; Root parasite; Strigolactones; Witchweed DOI: 10.7176/ALST/88-02 Publication date: July 31 st 2021

Striga species distribution and infestation in cereal food crops of northern Côte d’Ivoire

Most cereal food crops in Côte d'Ivoire are infested by Striga species. In this study the distribution, abundance and degree of infestation of Striga species were determined. Infested areas under cereal crops were estimated. Data was collected through extensive and intensive surveys and field visits. According to the updated map of Striga infestation, infested areas covered all the north of the country between latitudes 8°47.17' N to 10°38.84' N and longitudes 2°47.68' W to 7°55.20' W. The infested zone covered 3,191,850 hectares of farmland. 71.8% of the villages located in the region were infested by Striga species. The hypothesis of an extension of Striga infestations according to a north-south gradient was confirmed. Infestations began in the Sudan Savannah zone and have now reached half of the sub-Sudanian Savannah zone. Striga hermonthica, with a frequency of 97.1%, was the most abundant species under cereal crops, followed by Striga aspera (2.0%) and Striga asiatica (0.9%). Striga gesnerioides was not recorded on cowpea. Mutants of S. hermonthica and S. aspera with white flowers were identified. Red-flowered morphotypes of S. asiatica were found parasitizing upland rice. S. hermonthica is a major threat to cereal crop production in northern Côte d'Ivoire where it severely infested 57.2% (268,250 ha) of lands under maize (108,160 ha), millet (38,300 ha), sorghum (30,360 ha) and upland rice (91,430 ha). The infestation rates under millet, maize, sorghum and upland rice were 65.9%, 56.5%, 51.0% and 40.5%, respectively. Striga has today become a major national threat to the production of these cereals as well as to food security in endemic areas.

Infestation of crop fields by Striga species in the savanna zones of northeast Nigeria

Abstract Parasitism of crop plants by Striga species is a major constraint in the savanna zones of West Africa. Farmers ranked Striga as a leading constraint during a livelihood analysis of 30 communities in northeast Nigeria. A field survey was conducted to ascertain the extent of infestation by Striga spp. About 935 crop and fallow fields were surveyed across 30 communities in three agro-ecological zones. Four major Striga species were identified: Striga hermonthica in sorghum or maize; Striga aspera in rice; Striga densiflora in pearl millet and fallow and Striga gesnerioides in cowpea. About 68% of all fields sampled were infested, about 75% of compound fields and 60% of bush fields. The level of infestation was 60% in southern Guinea, 68% in Sudan and 74% in northern Guinea savanna. The level of infestation of cereal fields by S. hermonthica was in the order of Sudan savanna > Northern Guinea > Southern Guinea. Infestation of cowpea with S. gesnerioides was in the order of Northern Guinea savanna > Sudan savanna > Southern Guinea savanna. Across the three ecozones, about 85% of fields planted to maize and sorghum were infested with S. hermonthica and 81% of cowpea fields with S. gesenerioides. S. aspera infested 40–59% of rice fields and S. densiflora infested 27–60% of millet fields and fallow.

Evaluation of variability in Striga aspera, Striga hermonthica and their hybrids using morphological characters and random amplified polymorphic DNA markers

Striga aspera and Striga hermonthica are recognized as separate species, but their close morphological similarity causes difficulty in distinguishing between them in areas where they coexist in Africa. In this study, crosses between the species were made using randomly selected morphologically typical parental plants collected from different locations in Nigeria. Genetic analysis of both species and their reciprocal F1 hybrids were determined using cluster analysis of DNA profiles derived from genetic polymorphism (RAPD)‐polymerase chain reaction (PCR) markers. Principal component and hierarchical cluster analyses were used to separate parental and hybrid populations based on 13 morphological characteristics. Morphological data from wild samples of both species were compared with the hand‐pollinated parental, F1 and F2 hybrids, and back‐crosses. Results showed that S. aspera and S. hermonthica were genetically and morphologically distinct. Morphological and genetic analyses revealed two major clusters: a S. aspera cluster and a S. hermonthica cluster. Genetically, the F1 hybrids showed closer affinity to their maternal parents, while morphologically, the F1 hybrids formed distinct clusters intermediate to the parents. Most F2 plants and back‐crosses were morphologically similar to S. hermonthica. Comparative morphological analysis of wild and hand‐pollinated populations showed some samples from the wild clustered with the hybrids, suggesting that hybrids may exist in nature.

Tropical grasses vary in their resistance to Striga aspera, Striga hermonthica, and their hybrids

The genus Striga contains some of the most damaging parasitic plant species of the world, and it causes large problems in agricultural systems of Africa and Asia. Effective, cheap, and easy applicable methods for Striga control do not yet exist. One method with great potential may be the use of resistant crops. However, resistant crops are not widely available, hence, these genetic traits will have to be obtained from another source. Here we report the results of a screening in which it is shown that several native African savannah grass species possess a high level of resistance to Striga hermonthica (Del.) Benth., Striga aspera (L.) Kuntze, and interspecific hybrids of these two Striga species. This trait could be of potential value for the development of resistant crops. Resistance to Striga was not expressed at the levels of germination and attachment. Root exudates of all 14 grass species tested induced Striga seeds to germinate. Furthermore, attachment to the host roots was always observed. Subsequent development of the Striga seedlings, however, was absent or heavily impaired in resistant grasses. Preliminary observations suggested that the parasite could not breach the endodermal barrier of the roots. The host range of interspecific hybrids of S. aspera and S. hermonthica appeared to be a combination of the host ranges of their parents. They could not attack grass species that were resistant to both parents.Key words: Striga aspera, Striga hermonthica, interspecific hybrids, germination, attachment, tropical grasses, resistance.

Relationship between Smicronyx spp. population and galling of Striga hermonthica (Del.) Benth

Investigations were conducted in six farm fields (1.5 to 3 ha each) in Burkina Faso with objectives to (1) study adult Smicronyx spp. (Coleoptera: Curculionidae) population dynamics during Striga hermonthica (Scrophulariaceae) seed-pod production, (2) assess the impact of different population levels of Smicronyx spp. on St. hermonthica capsule production and, (3) estimate Smicronyx female reproductive success in seed-pod galls. A Univac portable sampler was used to sample adult Smicronyx spp. and St. hermonthica densities were assessed using a 1 m2 metal quadrat. Fifty St. hermonthica shoots per field were sampled each week. Before the emergence of St. hermonthica, Smicronyx adults were found on nearby Striga aspera (Willd) Benth. fields. Striga hermonthica shoots produced on average ca. 24 seed capsules each, while each female Smicronyx galled froml2 to 32 seed pods. Seed-pod galling alone was not sufficiently high to be considered as a successful reduction factor for St. hermonthica seed production in natural conditions. Smicronyx spp. adult population levels decreased during the St. hermonthica capsule production period. Increased population levels of Smicronyx spp. resulted in higher percentages of St. hermonthica seed-pod galls, suggesting that augmentative techniques, if used as part of an integrated control programme could be a worthwhile strategy.

Tropical grasses vary in their resistance to <i>Striga aspera</i>, <i>Striga hermonthica</i>, and their hybrids

Tropical grasses vary in their resistance to <i>Striga aspera</i>, <i>Striga hermonthica</i>, and their hybrids

Étude structurale et ultrastructurale de l'haustorium de Striga aspera (Willd.) Benth.

Summary Striga aspera (Willd.) Benth. (Scrophulariaceae) a parasitic plant on Sorghum (Sorghum vulgare L.) or on maize (Zea mays L.) in Senegal, is attached to host roots by suckers named haustoria. The mature haustorium, from the mother root to the host root, is divided into three areas: the vascular head, the vascular parenchymatous core and the endophyte (intrusive cells). The ultra- structure of these areas was studied by transmission electron microscopy. In the vascular parenchymatous core, the hyaline body shows intense meristematic and metabolic activity. The presence of numerous plasmodesmata in the cell walls of the parenchymatous cells of the cortex suggested that this tissue could play a key role in the metabolites transfer in place of phloem which was not identified in the haustorium of S. aspera.

GC/MS Evaluation of Compounds in Dry and Conditioned Striga Species Seeds

We have analyzed the dichloromethane (CH2Cl2) extracts of seeds of dry and conditioned Striga hermonthica (Del.) Benth., S. aspera (Willd.) Benth., and S. gesnerioides (Willd.) Vatke by means of gas chromatography (GC) coupled to mass spectrometry (MS). Sixteen compounds were identified on the basis of their mass spectra and their retention indices. All Striga spp. extracts contained tetradecanoic acid, cis,cis-9,12-octadecadienoic acid, cis-9-octadecenoic acid, and sitosterol. Also, 2,6-dimethoxy-p-benzoquinone (2,6-DMBQ) and several long chain aldehydes and n-hydrocarbons were detected in some of the extracts. The nature of the chemical changes induced by seed conditioning is discussed. Keywords: Striga aspera; S. hermonthica; S. gesnerioides; Scrophulariaceae; seed chemical constituents; CH2Cl2; GC/MS

Biochemical composition and photosynthetic activity of chloroplasts from Striga hermonthica and Striga aspera, root parasites of field‐grown cereals

Striga hermonthica(Del.) Benth. and Striga aspera (Willd.) Benth. are root parasites causing dramatic losses in field‐grown cereals in semi‐and tropics. Being achlorophyllous and obligate parasites during their underground development, upon emergence from the soil, they become green leafy plants; but, despite the presence of chlorophyll, they exhibit only low rates of photosynthesis. To investigate if deficiency in the photosynthetic apparatus could account for the low rates of photosynthesis, chloroplasts were isolated from S. hermonthica parasitizing sorghum [Sorghum bicolor (L.) Moench cv. Tiemarifing] and from S. aspera parasitizing maize (Zea mays L. cv. Tiémantié) grown under greenhouse conditions or in their natural surroundings. Isolated chloroplasts exhibited the characteristics of chloroplasts from C3 plants but displayed low levels of chlorophyll and polar lipids, while the protein content was less reduced. Main changes occurred in polar lipid composition, with decreases in monogalactosyldiacylglycerol and digalactosyldiacylglycerol. All polar lipids showed a decrease in the degree of unsaturation of fatly acids. All these changes were particularly pronounced in chloroplasts from plants that experienced heavy drought in Africa. On a chlorophyll basis, chloroplasts did not display a dramatic decrease in photosynthetic activities. These results are discussed in relation to parasitism and drought adaptation.