Drought-tolerant Desmodium species effectively suppress parasitic striga weed and improve cereal grain yields in western Kenya

Abstracts The parasitic weed Striga hermonthica Benth. (Orobanchaceae), commonly known as striga, is an increasingly important constraint to cereal production in sub-Saharan Africa (SSA), often resulting in total yield losses in maize (Zea mays L.) and substantial losses in sorghum (Sorghum bicolor (L.) Moench). This is further aggravated by soil degradation and drought conditions that are gradually becoming widespread in SSA. Forage legumes in the genus Desmodium (Fabaceae), mainly D. uncinatum and D. intortum, effectively control striga and improve crop productivity in SSA. However, negative effects of climate change such as drought stress is affecting the functioning of these systems. There is thus a need to identify and characterize new plants possessing the required ecological chemistry to protect crops against the biotic stress of striga under such environmental conditions. 17 accessions comprising 10 species of Desmodium were screened for their drought stress tolerance and ability to suppress striga. Desmodium incanum and D. ramosissimum were selected as the most promising species as they retained their leaves and maintained leaf function for longer periods during their exposure to drought stress conditions. They also had desirable phenotypes with more above ground biomass. The two species suppressed striga infestation, both under controlled and field conditions, and resulted in significant grain yield increases, demonstrating the incremental capability of Desmodium species in striga suppression. These results demonstrate beneficial effects of Desmodium species in enhancing cereal productivity in dry areas

A climate-adapted push-pull system effectively controls fall armyworm, Spodoptera frugiperda (J E Smith), in maize in East Africa

Fall armyworm, Spodoptera frugiperda (J E Smith), an economically important pest native to tropical and subtropical America has recently invaded Africa, causing substantial damage to maize and other crops. We evaluated functionality of a companion cropping system, ‘climate-adapted push-pull’, developed for control of cereal stemborers in drier agro-ecologies, as an added tool for the management of fall armyworm. The technology comprises intercropping maize with drought-tolerant greenleaf desmodium, Desmodium intortum (Mill.) Urb., and planting Brachiaria cv Mulato II as a border crop around this intercrop. Protection to maize is provided by semiochemicals that are emitted by the intercrop that repel (push) stemborer moths while those released by the border crop attract (pull) them. 250 farmers who had adopted the technology in drier areas of Kenya, Uganda and Tanzania were randomly selected for the study during the long rainy season (March-August) of 2017. Each farmer had a set of two plots, a climate-adapted push–pull and a maize monocrop. Data were collected in each plot on the number of fall armyworm larvae on maize, percentage of maize plants damaged by the larvae and maize grain yields. Similarly, farmers' perceptions of the impact of the technology on the pest were assessed using a semi-structured questionnaire. Reductions of 82.7% in average number of larvae per plant and 86.7% in plant damage per plot were observed in climate-adapted push-pull compared to maize monocrop plots. Similarly, maize grain yields were significantly higher, 2.7 times, in the climate-adapted push-pull plots. Farmers rated the technology significantly superior in reducing fall armyworm infestation and plant damage rates. These results demonstrate that the technology is effective in controlling fall armyworm with concomitant maize grain yield increases, and represent the first documentation of a technology that can be immediately deployed for management of the pest in East Africa and beyond

Qualitative Distribution of Candidatus Phytoplasma Oryzae in Roots, Stems and Leave of Napier Grass (Pennisetum purpureum)

For sustainable production of Napier grass (Pennisetum purpureum), screening for the absence of phytoplasma on propagation material (stem) is carried by Nested-PCR in detection of 16S rDNA on leaves.  However, the aim of this study was to investigate if there is uneven distribution of the pathogen in roots, stems and leaves of the infected plants that could influence screening results. A total of 294 Napier grasses infected with candidatus phytoplasma oryzae were sampled from western Kenya for detection of Napier Stunt Disease (Phytoplasma Oryzae) by nested PCR. There was significant difference on distribution of phytoplasma in roots, stems and leaves (F=36.26, df=2, p<0.001). The results show that high number of positive samples were detected from stem (94.1 %), leaves (77 %) and roots (44.1 %) samples, respectively. Conclusively, the study revealed uneven distribution thus inclusion of stem samples should be considered during screening procedures. Other factors like seasonal variation are also essential to be studied. Keywords: Phytoplasma, Napier grass, nested PCR, Distribution of the pathogen, Propagatio

Homecoming of Brachiaria: Improved hybrids prove useful for African animal agriculture

Species of the genus Brachiaria originate primarily from Africa, where they are constituents of natural grasslands. Due to their adaptation to acidic, low-fertility soils, millions of hectares of Brachiaria species have been sown as improved pastures in South and Central America, especially B. brizantha cv. Marandu and B. decumbens cv. Basilisk. Due to B. decumbens' susceptibility to spittlebug insect pests in the Americas, CIAT in Colombia and EMBRAPA in Brazil initiated breeding programmes in the 1980s. First cultivars released from CIAT's breeding programme – cvs. Mulato and Mulato-II – have also been investigated in African countries. They have been examined for integration in conservation agriculture systems (Madagascar), for drought and acidic soil tolerance (Rwanda) and for intercropping forages in dairy systems (Uganda, Madagascar), among others. Seed sales to African countries suggest that an area of at least 1,000 ha has been sown so far. The largest adoption of cv. Mulato-II is currently happening in eastern Africa, where it is used by over 20,000 farmers as a trap plant in the push-pull system for control of maize stem borers and parasitic Striga weed. Cv. Mulato-II's particular advantage is its relatively high crude protein content due to greater leafiness and thinner stems than those of traditional Napier grass, resulting in higher nutritive quality. Yet new pest challenges have emerged, requiring further research attention. Diverse hybrids are in the pipeline for release, among them those that are suitable for cut-and-carry systems which are prevalent in eastern Africa. This paper reviews research, development and incipient adoption of new Brachiaria hybrids in African countries. (Résumé d'auteur

Genotypic response of brachiaria (Urochloa spp.) to spider mite (Oligonychus trichardti ) (Acari: Tetranychidae) and adaptability to different environments

Grasses in the genus Urochloa, commonly known as brachiaria, are grown as forage crops in sub-Saharan Africa, with some genotypes being used in management of insect pests. However, spider mite, Oligonychus trichardti Meyer (Acari: Tetranychidae), has recently been reported as its major pest in the region. We evaluated 18 brachiaria genotypes to identify sources of resistance to O. trichardti, and to determine their adaptability to different environments in western Kenya. Response to artificial infestation with O. trichardti was evaluated under controlled conditions in a screenhouse while adaptability to different environments and field resistance to mites was evaluated in three locations for two cropping seasons in 2016 and 2017 under farmers’ conditions. The parameters evaluated as indicators of resistance to pest damage included leaf damage, chlorophyll content reduction, plant height, leaf area, number of tillers and shoot biomass. Rainfall played a role in reducing mite infestation and increasing biomass yield of the genotypes. Significant correlations between parameters were only observed between leaf damage and yield (r = -0.50), and leaf damage and chlorophyll loss (r = 0.85). The cultivar superiority index (Pi) ranked Xaraes, Piata, ILRI 12991 and ILRI 13810 as reliable genotypes that combined moderate resistance to the mite (Pi ≤ 48.0) and high biomass yield (Pi ≤ 8.0). Since this is the first documentation of interactions between O. trichardti and different brachiaria genotypes, we propose these genotypes as potential candidates for improved forage yields in areas prone to O. trichardti infestation in Africa

Signal Grass (Brachiaria brizantha) Oviposited by Stemborer (Chilo partellus) Emits Herbivore-Induced Plant Volatiles That Induce Neighbouring Local Maize (Zea mays) Varieties to Recruit Cereal Stemborer Larval Parasitoid Cotessia sesamiae

Plants respond to attack by herbivores with the release of herbivore-induced plant volatiles (HIPVs). In return, natural enemies (predators and parasitoids) respond to these emitted herbivore-induced plant volatiles while foraging for their hosts. Neighboring plants of the same family may be induced by the emitted HIPVs. This is a tritrophic interaction that leads to a

Do NERICA rice cultivars express resistance to Striga hermonthica (Del.) Benth. and Striga asiatica (L.) Kuntze under field conditions?

The parasitic weeds Striga asiatica and Striga hermonthica cause high yield losses in rain-fed upland rice in Africa. Two resistance classes (pre- and post-attachment) and several resistant genotypes have been identified among NERICA (New Rice for Africa) cultivars under laboratory conditions (in vitro) previously. However, little is known about expression of this resistance under field conditions. Here we investigated (1) whether resistance exhibited under controlled conditions would express under representative Striga-infested field conditions, and (2) whether NERICA cultivars would achieve relatively good grain yields under Striga-infested conditions. Twenty-five rice cultivars, including all 18 upland NERICA cultivars, were screened in S. asiatica-infested (in Tanzania) and S. hermonthica-infested (in Kenya) fields during two seasons. Additionally, a selection of cultivars was tested in vitro, in mini-rhizotron systems. For the first time, resistance observed under controlled conditions was confirmed in the field for NERICA-2, -5, -10 and -17 (against S. asiatica) and NERICA-1 to -5, -10, -12, -13 and -17 (against S. hermonthica). Despite high Striga-infestation levels, yields of around 1.8 t ha−1 were obtained with NERICA-1, -9 and -10 (in the S. asiatica-infested field) and around 1.4 t ha−1 with NERICA-3, -4, -8, -12 and -13 (in the S. hermonthica-infested field). In addition, potential levels of tolerance were identified in vitro, in NERICA-1, -17 and -9 (S. asiatica) and in NERICA-1, -17 and -10 (S. hermonthica). These findings are highly relevant to rice agronomists and breeders and molecular geneticists working on Striga resistance. In addition, cultivars combining broad-spectrum resistance with good grain yields in Striga-infested fields can be recommended to rice farmers in Striga-prone areas