icipe - MESHA

By Christine Ochogo I christawine@gmail.com

Every season, Margaret Kenzi, a potato farmer in Kenya’s Rift Valley, tirelessly works in her potato farm with hopes of a bumper harvest.

To her dismay, her efforts of three years have hardly yielded as she does not use certified potato seeds. She attributes this sorry state to the high cost of certified seeds, which has driven her to use regenerated seeds every planting season that are prone to attacks by pests and diseases.

“I depend on recycled seeds because certified seeds cost Sh3,000 (U$30) per bag of 50kg which I cannot afford due to the hard economy. And after harvesting, we are forced to sell our produce at a throwaway price to middlemen and brokers who invade our farms with ready cash. A 50kg bag of potatoes goes for between Sh1,500 (U$15) and Sh2,000 (U$20) while a 2kg package sells at Sh100 (U$1),” decries Kenzi.

Researchers put it that only maize is grown in more countries than potato, with Africa producing about seven percent of global potato output, mainly in Egypt and South Africa. The crop is popular and valuable for both food security and income generation, competing well with maize in the subtropical climates at higher altitudes.

Under these conditions, year-round production can be possible, often with at least two seasons per annum. In recent years, however, yields have shown notable declining trends, mainly attributed to major disease outbreaks, inappropriate cropping practices by farmers, substandard seed quality, and lack of organized market infrastructure for produce.

Emerging markets for processed potatoes (such as chips, crisps, starch) have increasingly focused attention on the crop, with rising demand from the fast-food industry and processing for added economic value. Processed potatoes, however, also demand high levels of quality, which can be difficult to sustain in the face of high pest and disease pressures.

In Kenya, according to Farming Success with Potatoes in Kenya, a publication by the International Centre of Potato (CIP), potato is the second most important staple food crop after maize and is valued at nearly $500 million (Sh50 billion) annually.

About 800,000 Kenyans directly benefit from potato production, while across the whole value chain about 2.5 million people receive income from potato. However, in Kenya, yields have declined and currently average 9-10 tonnes per hectare, much below the potential of 20–40 t/ha, and this is reflected across the region.

As if Mother Nature is adding insult to injury, farmers like Ms. Kenzi’s woes are not helped by the emergence of new pests and diseases, such as the recently detected potato cyst nematodes (PCNs), Globodera rostochiensis and G. pallida, a key threat to potato production in eastern Africa, according to an article published recently in the Frontiers in Plant Science journal by International Centre of Insect Physiology and Ecology (icipe); International Institute of Tropical Agriculture (IITA); North Carolina State University, USA; and Kenyatta University, Kenya.

The occurrence of PCN presents a key threat to potato production in Kenya, as well as to the entire East Africa region where potato features prominently as a food security or income generation crop for millions of smallholder farmers. The good news, states the study in its conclusion, is that it may be possible to manage the nematodes by inducing ‘suicidal hatching’ of the pests using naturally occurring chemicals in crop roots.

Nematodes are tiny microscopic worms, with some soil-dwelling species infecting and adversely affecting most, if not all, cultivated crops. Potato cyst nematodes (PCNs) are invasive nematode pests that were first reported in Kenya in 2015 and have since been confirmed from other countries in eastern Africa.

Studies by icipe and partners have shown that these nematodes cause up to 80 percent yield loss in potatoes.

“The management of the nematodes understudy is particularly challenging due to the pest’s ability to survive in the soil as tiny protective cysts. These cysts can contain up to 600 eggs but are able to remain dormant in the absence of a host plant for up to 20 years. Once they infest a field, it is impossible to eradicate. Therefore, a possible effective approach is to avoid the build-up and spread of the pest,” says Prof Baldwyn Torto, Head of Behavioural and Chemical Ecology Unit at icipe.

In over 100 countries, this has been achieved by strict quarantine regulations because they are globally considered as the most important pests threatening potato production but are all too often overlooked in less developed countries.

The recent studies by icipe and partners aimed to manage their spread by exploring several known facts about potato cyst nematodes. First, is the fact that potato cyst nematodes eggs hatch only in the presence of suitable host plants such as potato, tomato, and African nightshade, which scientists refer to as the Solanaceae family.

Once hatched, the infective juvenile nematodes that emerge from the cyst seek host crop roots to invade and feed upon. The developing female nematodes swell and eventually become a new cyst full of eggs. These eggs hatch only once triggered by chemical signals produced by the roots of the host plant. The aim of the research was to identify these signals, and whether they can be exploited to induce hatch of the potato cyst nematodes juveniles in the absence of host crops and thus lead to their eventual death; or rather the ‘suicidal hatch’ of the nematodes.

“We noted that most juvenile PCN that hatched in response to some chemical signals, known as steroidal glycoalkaloids (SGAs) and steroidal alkaloids (SAs), remained encysted. In other words, they did not leave the cyst to invade crop roots but remained encapsulated in the cyst,” noted a Kenyan scientist, Juliet Ochola, who was involved in the research as part of her MSc studies, based at icipe and registered at Kenyatta University.

Prof Danny Coyne, a soil health scientist at IITA, explains that the SGAs and SAs could be used in synthetic forms to stimulate suicidal hatch of PCN in infested fields before farmers plant potatoes.

Alternatively, plants that produce the chemicals but are not usually infected by PCN could be incorporated in a crop rotation system to stimulate PCN hatch, thereby reducing populations of the pest.

“Blends of the compounds obtained from crude material of such plants may be used to treat potato fields as organic soil amendments. This approach would be environmentally attractive and better than using nematicides, which can be hazardous, and due to their dependence on single compounds, are prone to pest resistance,” says Prof Coyne.

The study presents the results of a countrywide survey undertaken to determine the distribution of PCN and the potential damage it is causing in the major potato growing regions of Kenya.

Additionally, the study team examined farmers’ potato production practices and how these will need to be taken into consideration for the implementation of future pest management strategies.

It is hoped that the information provided in the study will serve as a wakeup call that should further help policymakers and regional stakeholders to make informed decisions related to PCN containment and mitigation.

The fall armyworm is a moth that causes devastating damage to almost 100 plant species, including sorghum, rice, wheat and sugarcane, thereby threatening food and nutritional security, trade, household incomes and overall economies. The fall armyworm spreads very fast – in its adult stage it can move over 100 kilometres in a single night. The pest is also capable of laying hundreds of eggs, with the emerging larvae burrowing into crops, destroying and eventually killing the plants.

Until 2016, the fall armyworm was constrained to its native region of origin, the Western Hemisphere (from the United States of America to Argentina). However, in January 2016, the pest was reported in Nigeria and it has since spread at an alarming rate across Africa; its presence has been confirmed in more than 28 African countries, while a further nine either strongly suspect, or are awaiting confirmation of invasion.

Already, in less than 2 years, the impact of the fall armyworm is being felt across Africa. Estimates from 12 African countries indicate that the pest is causing annual maize losses of between 8 and 21 million tonnes, leading to monetary losses of up to US$ 6.1 billion, while affecting over 300 million people in Africa, who, directly or indirectly, depend on the crop for food and well-being. The pest’s impact is likely to be even higher when its damage on other crops is quantified.

This new menace piles onto a range of existing challenges afflicting Africa. For instance, many regions of the continent are already experiencing the impacts of climate-change, including drier and hotter weather, stressed out soils, various invasive pests such as Tuta absoluta, and increased outbreaks of existing pests such as stemborers and the parasitic Striga weed.

“Efforts to control the fall armyworm through conventional methods, such as use of insecticides is complicated by the fact that the adult stage of the pest is most active at night. The pest also has a diverse range of alternative host plants that enables its populations to persist and spread. Moreover, fall armyworm has been shown to develop resistance to somewhile the performance of such chemicals is also hindered by limited knowledge and purchasing power of farmers, resulting into use of low quality, and often harmful products,” notes icipe scientist, Dr Charles Midega.

A recent study has established that a climate-adapted version of Push-Pull, an already widely used technology developed by icipe and partners is effective in controlling the fall armyworm, providing a suitable, accessible, environmentally friendly and cost-effective strategy for management of the pest.

Push-Pull, an innovative companion cropping technology developed over the past 20 years by icipe in close collaboration with national partners in eastern Africa and Rothamsted Research, United Kingdom, is modelled along the African smallholder farming system of multiple cropping. Originally developed for the control of stemborers, the key pests of cereal crops across most of Africa, and the parasitic Striga weeds, Push-Pull involves intercropping cereal crops with insect repellent legumes in the Desmodium genus, and planting an attractive forage plant such as Napier grass as a border around this intercrop. The intercrop emits a blend of compounds that repel (‘push’) away stemborer moths, while the border plants emit semiochemicals that are attractive (‘pull’) to the pests. Push-Pull has recently been adapted to drier areas through the incorporation of drought tolerant companion plants: Greenleaf Desmodium as an intercrop and Brachiaria cv Mulato as a border crop. In addition, Push-Pull also controls maize ear rots and mycotoxins, while improving soil health and providing high quality fodder, since the companion crops are superior forages. Therefore, the technology facilitates crop-livestock integration thus expanding farmers’ income streams.

“Over the past several months we received information from Push-Pull farmers that their fields were free of fall armyworm infestation while neighbouring monocrop plots were being ravaged by the pest. Therefore, we evaluated the climate-adapted version of the technology as a potential management tool for fall armyworm in Kenya, Uganda and Tanzania,” explains Prof. Zeyaur Khan, Push-Pull leader at icipe.

The study revealed fall armyworm infestation to be more than 80% lower in plots where the climate-adapted Push-Pull is being used, with associated increases in grain yields, in comparison to monocrop plots. The findings were supported by farmers’ perceptions through their own observations regarding significantly reduced presence of fall armyworm in Push-Pull plots.

“The ability to manage such a devastating pest clearly demonstrates Push-Pull’s utility as a platform technology in addressing the multitude of challenges that affect cereal-livestock farming systems in Africa. icipe intends to continue disseminating the technology as widely as possible across Africa, while advancing studies to understand the scientific basis of its effectiveness against the fall army worm,” says icipe Director General, Dr Segenet Kelemu.