Fighting maize lethal necrosis disease

Dr Boddupalli Maruthi Prasanna, the Global Maize Programme director at the Maize and Wheat Improvement Centre (CIMMYT), and also the director of Consultative Group for International Agriculture Research (CGIAR) programme, MAIZE, spoke to Brian Okinda on Maize Lethal Necrosis disease.

What is the current situation on the spread and control of Maize Lethal Necrosis Disease in Kenya and eastern Africa? What are its effects on food security?

A recent survey indicates that the incidences countrywide were 28.5 per cent.

Regionally, MLND is still in Kenya, Uganda, Tanzania, Rwanda and Ethiopia, with an average prevalence of 27.5 per cent.

The Democratic Republic of Congo, Burundi and South Sudan have also showed signs of the disease although these are not covered in the MLN Diagnostics and Management project implemented by International Maize and Wheat Improvement Centre and other partners.

Malawi, Zambia, Zimbabwe and Mozambique are all free from the disease.

What are the symptoms of the disease? How is it spread and what preventive measures can farmers take?

Its symptoms include severe chlorosis or loss of green colouration on leaves and their mottling. It usually leads to necrosis (dead plant parts)

The necrosis starts at the leaf margin and progresses to the interior. Other symptoms are formation of sterile tassels with no pollen production, premature drying of husks and poor or no grain filling.

Death of young leaves in the whorl results in the “dead heart” symptoms. Severely affected plants die prematurely or form small cobs/ears with little or no grain.

The predominant of the two MLND-causing viruses — MCMV and SCMV — is MCMV. It can survive in soil or plant debris as virions and can be transmitted through plant tools. It has to be introduced to a living cell to reproduce.

The disease can spread from plant to plant by mechanical/sap transmission, whereby viruses in the sap are passed from an infected plant to a healthy one through a ‘wound’.

Transmission also occurs through insect vectors like aphids, thrips and leaf beetles and infected or contaminated seed.

While reports from early research on seed transmission in the US indicate seed-borne transmission occurs at very low rate, results from East Africa indicate a much higher frequency.

CIMMYT and other organisations have advanced several MLN management practices in farmers’ and in seed fields. What are these practices?

The practices being disseminated, include detailing MLND’s typical symptoms and how to manage the disease.

Farm tools and implements should be disinfected before they are used in new fields.

Practising a closed maize season of at least two months, where applicable, and crop rotation for at least one season with non-cereal crops, preferably legumes, is important.

The use of certified maize seed produced in an MLND-free environment is also important. Seeds from previous crop or from other sources other than commercial seed dealers should be avoided, especially in MLN-endemic areas.

Seeds from MLND-infected maize plants or fields should not be used for planting.

Avoid feeding MLND-infected plants to livestock. Removing infected plants from fields and burning them prevents the spread of the virus to other plants through insect vectors.

Involving agriculture experts and officials on appropriate control measures is advisable.

CIMMYT, together with the Alliance for a Green Revolution in Africa (AGRA), African Agricultural Technology Foundation (AATF) and through consultations with important stakeholders in the maize value chain also developed MLND-free seed production checklists used by seed companies and their contract farmers to produce MLND-free seed in endemic regions.

Your organisation and other research institutions have developed varieties resistant or tolerant to MLND. Which are these varieties and how accessible are they?

There are about 15 varieties of maize deemed resistant to the virus causing the disease.

These are Bazooka (UH5354) released in 2014 in Uganda, H12ML and H12ML produced by Kenya Seed Company, Meru HB607 expected to be produced by Meru-Agro in Tanzania, WE5135, WE5140, WE6109, WE6110, KATEH16-01, KATEH16-02, KATEH16-03, WHMLN, WE7117, WE7118 and WE7119, which are all recommended for licence, production, certification and release through Kenya Agricultural and Livestock Research Organisation in collaboration with Agri-Seed and Western Seed Company.

Despite progress made in fighting the disease, there is a resurgence of MCMV in Uganda which could spread to Kenya. Why is this so?

One probable reason is that previous surveillance mechanisms may not have been exhaustive enough to detect the exact points of MLND incidences in the country.

It is likely that the most recent and intensive survey with more sampling points have led to more detailed results.

Another possibility is the spread of MLND through infected seed.

MLND thresholds in commercial seed production fields and on packaged seed are not encompassed in regulations for maize seed certification in Uganda.

Likewise, it seems checklists for production of MLND-free seed is still not fully observed by some companies.

What are the repercussions for using recycled and farm saved maize seeds as opposed to certified seeds?

Recycled and farmer-saved seeds are not certified. Chances of such seed being contaminated with MLN-causing viruses are high.

Plants from these seeds are weak for they do not typically have the same vigour as hybrids. Such crops are more vulnerable to biotic and abiotic stresses, resulting in low yields.

There are regulatory procedures governing production and release of high quality maize varieties to farmers. What is your opinion?

Regulatory agencies are sensitive to the needs of farmers. Their efforts should be intensified as new varieties with improved genetics are needed to replace those developed and more than 15 to 20 years ago.

This process, called varietal turnover, is important in increasing maize productivity and resilience to climate-induced stresses. Varietal turnover has to be supported by seed companies.

Are the varieties developed also resilient to adverse ecological conditions like drought, heat, poor soils, waterlogging, acidity and weeds?

There are hybrids that show MLN and drought tolerance like Bazooka. Other hybrids that are MLN tolerant are in various stages of release.

Breeding for fall armyworm has just been initiated and will take a while to have elite varieties completely resistant to the pest.