Germplasm Bred for Resistance to Striga hermonthica Exhibited High Resistance Levels to Striga asiatica Compared to Commercial Checks

Parasitic weeds belonging to the Orobanchaceae family are a menace in Sub-Saharan African (SSA). Specifically, the two witchweeds from the genus Striga, S. hermonthica and S. asiatica, are jointly responsible for land abandonments and cereal yield reductions in the SSA. Factorial experiments involving fourteen maize genotypes and two levels of Striga asiatica infestation (infested and noninfested) were conducted under pot and laboratory experiments at the Department of Plant Production Sciences and Technologies, University of Zimbabwe, during the 2014/2015 season. A 14 × 2 factorial pot experiment was arranged in a 7 × 4 α-lattice design replicated four times, whereas the laboratory agar gel was arranged in a complete randomized design with four replications. Results revealed significant differences ( p < 0.05) for S. asiatica and genotype main effects for the recorded traits. S. asiatica-infested genotypes had lower biomasses than noninfested ones. However, the University of Zimbabwe bred hybrids such as Ax31, Ax28, Ax7, and Ax32 had similar plant heights and stem, leaf, and cob biomass across the two Striga levels unlike the local checks, particularly SC513, SC537, and SC637, under Striga infestation. Moreover, these genotypes also had the least Striga germination percentage and furthest germination distance indicating that they are resistant/tolerant to Striga asiatica. The University of Zimbabwe bred hybrids, using Striga hermonthica resistance from the International Institute of Tropical Agriculture, exhibited resistance/tolerance to Striga asiatica compared to local checks. Therefore, these varieties could offer a better and viable Striga spp. control option to farmers in both S. hermonthica and S. asiatica endemic areas.

Identifying cultural, climatic and temporal factors influencing Striga asiatica abundance within rice--maize systems in mid-west Madagascar

The parasitic weed genus Striga causes huge losses to crop production in sub-Saharan Africa, estimated to be in excess of $7 billion per year, affecting subsistence farmers who frequently lack access to novel technologies proposed for control. Effective Striga management therefore requires the development of strategies utilising existing cultural and management practices. We report a multi-year, landscape-scale monitoring project for Striga asiatica in the mid-west of Madagascar, undertaken over 2019-2020 with the aims of examining cultural, climatic and edaphic factors currently driving abundance and distribution. Long-distance transects were established across the middle-west region of Madagascar, over which Striga asiatica abundance in fields was estimated. Analysis of the data highlights the importance of crop variety and legumes in driving Striga density. Moreover, the dataset revealed significant effect of precipitation seasonality, mean temperature and altitude in determining abundance. A composite management index indicated the effect of a range of cultural practices on changes in Striga abundance. The findings support the assertion that single measures are not sufficient for the effective, long-term management of Striga. Furthermore, the composite score has potential as a significant guide of ISM control beyond the geographic range of this study.

Genome-Wide Association Studies for Striga asiatica Resistance in Tropical Maize

Striga asiatica L. is a parasitic weed in cereal crops including maize leading to tremendous yield losses up to 100% under severe infestation. The available S. asiatica control methods include cultural control options such as uprooting and burning the Striga plants before they flower, field sanitation, crop rotation, intercropping, organic matter usage, improved fallows, and application of herbicides. Resource limitation among smallholder farmers renders almost all of the control methods impossible. Development and use of Striga resistant genotypes are seen as the most feasible management option. Marker identification formulates tools that are faster, cheaper, and easier to utilise in breeding for S. asiatica resistance which has low heritability. The objective of this study was to identify single nucleotide polymorphism (SNP) markers for Striga resistance using the genome-wide association study (GWAS). Genotyping by sequencing was done on tropical maize inbred lines followed by their evaluation for Striga resistance. Analysis of variance showed significant ( p < 0.05 ) variation among evaluated genotypes for Striga resistance traits such as germination distance, germination percentage, haustoria root attachments, total Striga plants emerged, total biomass, and growth rate. There were also significant differences ( p < 0.05 ) for cobs, leaves, stems, and roots weight. The broad sense heritability was fairly high (up to 61%) for most traits. The means for derived traits on stress tolerance indices were subjected to a t -test, and significant differences ( p < 0.05 ) were found for leaves, stem, roots, shoots, and total biomass. The Manhattan plots from GWAS showed the presence of three SNP markers on chromosome numbers 5, 6, and 7 for total Striga plants emerged. The identified markers for resistance to S. asiatica should be validated and utilised to breed for Striga resistance in tropical maize.

Striga asiatica (witch weed).

S. asiatica is a hemiparasitic plant, native to Africa and Asia. In common with most other parasitic weeds, it is not especially invasive in natural vegetation, but is much feared in crop land where infestations can build up to ruinous levels, especially with repeated growing of susceptible cereal crops. For this reason it is included in almost all lists of noxious, prohibited plant species. It has recently been reported in Queensland, Australia. There is also evidence for its continuing spread and intensification within a number of countries in Africa in particular in rice in Tanzania and maize in Malawi. A study by Mohamed et al. (2006) suggests that on the basis of climatic data, there are many territories into which Striga species, including S. asiatica, could be introduced and thrive. Global warming could further increase this potential.

Breeding Strategy for Resistance to Striga Asiatica Based on Genetic Diversity and Population Structure of Tropical Maize Lines

Maize (Zea mays L.) is a major staple crop in southern Africa and is produced on millions of hectares. However, its yield is greatly reduced by Striga spp, a parasitic weed which is causing US$ 7 billion losses annually. Use of host resistance could be an effective way of controlling Striga and resistance to Striga is quantitative, mainly controlled by additive gene action. Understanding the population structure and genetic diversity is therefore key in designing an effective breeding program targeting grain yield heterosis and resistance to Striga. The aim of this study was to determine the genetic diversity and population structure of the key germplasm from tropical Africa. This information could guide in the identification of heterotic groups and potential testers required to kick start a maize breeding program for Striga asiatica in southern Africa. A total of 222 maize inbred lines from IITA and CIMMYT were used in this study. The materials were genotyped using the genotyping-by-sequencing method. A total of 45 000 SNP markers were revealed, and these were subjected to analysis of molecular variance, structure analysis and clustering using the Gower’s distance and neighbor joining algorithm. Molecular variance was lager within individuals (91%) than among populations (9%). The inbred lines clustered into three major groups, with the IITA germplasm clustering separately from CIMMYT germplasm. A breeding strategy for Striga asiatica resistance was proposed with the aim of increasing genetic gains in both the resistance and grain yield.

Impact of mulch-based cropping systems using green mulch and residues on the performance of advanced mutant lines of maize (Zea mays (L.)) under infested field with the parasitic weed Striga asiatica (L.) Kuntze in Madagascar.

In Madagascar, cereal yields remain insufficient due to various biotic and abiotic constraints, including Striga asiatica, a parasitic weed that has contributed to decreased maize yield up to 100%. This work aims to assess the impact of the practice of two cropping systems on the maize crop infested by S. asiatica. PLATA maize seed of the putative tolerant mutant line from the M5 generation after gamma irradiation at 100, 200 and 300 Gy and of the sensitive parent variety were grown in fields naturally infested or artificially inoculated with one pinch of around 3000 ready-to-germinate seeds of S. asiatica. The cropping system (SCV) is a community of plants that is managed by a farm unit to achieve various human goals. The residue of Stylosanthes sp. legumes was used as mulch SCVm and the legume cowpea was planted with the host plant for the intercropping system SCVv. Results have shown that the use of mulch, either residue SCVm or green mulch SCVv, minimizes S. asiatica infestation on maize plants. The SCV reduces significantly the number of emerging Striga plants with an emergence of 1.33 ± 0.36 for SCVm, 4.33 ± 0.27 for SCVv and 15.00 ± 1.08 for the control. Moreover, M5 lines have shown significant differences in plant survival rate of 50.57 ± 1.25% to 80.00 ± 0.91%, versus 13.50 ± 0.47% for the parent variety. Yields of the parent and M5 lines on SCVm are, respectively, 3.46 ± 0.02 t/ha and 4.64 ± 0.01 t/ha, and 2.30 ± 0.04 t/ha and 3.61 ± 0.05 t/ha for SCVv, while that of the control plot remains low, varying from 0.50 ± 0.04 t/ha to 2.29 ± 0.01 t/ha. Cover increases soil humidity and delays the development of S. asiatica and infection of the host plant, thus improving host plant yield. These results demonstrate the benefit of the integrated approach of mutation breeding and cultural practice to ensure more durable crop production under heavy Striga infestation.

Some noteworthy plants record to the flora of Yavatmal district, Maharashtra, India

The present paper deals with the addition of 05 new plant species i.e. Tephrosia pumila, Striga asiatica, Tecomella undulata, Orobanche cernua and Sauromatum venosum belonging to 05 different families; from this 01 additional family i.e. Orobanchaceae is reported for the first time to the flora of Yavatmal district. This study provides the correct and updated detail information about morphology, phenology and occurrence of these new additional plant species for the future work.