2013. ceballos. cassava diseases

How to get high and stable yields in cassava?

Dealing with diseasesHernán Ceballos

2nd Starch World 2013Jakarta, Indonesia

(February 2014)

How to get high and stable yields in cassava?

Use improved,high-yielding

varieties

Quality of planting material

Adequate weed control

Timely land preparation

Timely planting

Soil fertility

Pest and diseases

How to manage the problem of diseases in cassava?

Identification of the pathogen

Understanding the pathogen

Avoiding the pathogen

Controlling the pathogen

Identifying the pathogen

It is the first step for defining adequate management practices

In most cases the identification is veryeasy and fast, but not always….

Viral diseases

Cassava mosaic disease (CMD): a devastating disease in Africa /India.

Cassava brown streak (CBSD): a growing.problem in Eastern Africa

Super elongation disease.

Cercospora leaf spot

Fungal diseases

Root rots

Bacterial diseases

Cassava bacterial blight

Unknown pathogen: “frog skin disease”

Suspects: a virus (complex), phytoplasm or bothTransmitted by the use of cuttings from diseased plants There must be an (unknown) vector transmitting it from infected to healthy plants

Unknown pathogen: “witches´broom”

Most likely induced by a phytoplasmTransmitted by the use of cuttings from diseased plants There must be an (unknown) vector transmitting it from infected to healthy plants

Identifying the pathogen

It is the first step for defining adequate management practices

In most cases the identification is veryeasy and fast, but not always….Once the pathogen is identified proper control strategies can be implemented


Key elements in the disease cycle are:

The source of inoculum

Mealy bug in planting material Stems with witches´ broom



The source of inoculumThe ways of transmission

Insects (particularlywhite flies) are important vectors

The cuttings are the most common

way of transmission

Tools may transmitdiseases



The source of inoculumThe ways of transmission

Environmental factors that influence it

Water logging conditions promote root rots

In general, adequate

fertilization will allow the plant to

defend itself(particularly in

relation to K)

NEVER introduce into a country vegetative material

For centuries cassava production in Asia has benefitted from little disease and pest pressuresThe best situation is when the cassava plant does not have to face a source of biotic stressHowever, this implies that Asian cultivars are most likely susceptible to the diseases they have never facedRecent events demonstrate the risk of unsupervised movement of planting material


The introduction inAsia of the mealybug (from Africaor southern Brazil) illustrates the huge economic damage that introducing new pests or diseases into Asia can have


Has frog skin disease been introduced into Asia?


This restriction isalso applicable to relatives of cassava such as Jathrofa

Avoiding the pathogen can also be achieved through good quality

planting material

… so it may be convenient to clean knives and machetes

Tools may transmitdiseases

El “Rincón de la Fortuna”The “Corner of Prosperity”

A good variety is not enough to have high andstable yields

The objective of most cassava breeding is toproduce varieties that can efficiently take advantage of whatever the environment canoffer to them

The best racing car still needs gasoline for winning a race…

Farmers select the best area of the field (typically10%)Special care (proper weeding + fertilizers) in that areaElimination of diseased plants (e.g. witches broom)

Inspection of the roots (e.g. good yield or diseases)


Harvest the Corner of Prosperity just before planting material for the new cycle is required

At harvest take stems ONLY from productive plants

Visual inspection of

root health (e.g. rots, frog

skin, etc.)

Farmers select the best area of the field (typically10%)Special care (proper weeding + fertilizers) in that areaElimination of diseased plants (e.g. witches broom)

Inspection of the roots (e.g. good yield or diseases)


Take stems only from plants after root inspection

Harvest the Corner of Prosperity just before planting material for the new cycle is required

High-yielding variety +

Good quality planting material



Several strategies can be used to slow down or reduce the impact of diseases:

Chemical protection of cuttings or the plant

Chemical control

Chemical protection of cuttings with fungicides and pesticides is sometimes necessary (+

nutrients…)

But has to be done responsibly…


Thermotherapy of the cuttings can be useful for some diseases , buttemperature needs to be checked very carefully….

If things are done properly, however, chemical protection to the plant is seldom necessary in cassava

Chemical control




The use of resistant varieties

Cassava mosaic disease (CMD): a devastating virus for cassava in Africa and India.

ResistantSusceptible

CBSV(Cassava brown streak virus)

“Clean”Infected

It should be mentioned that it is possible to producetransgenic cassava… and one of the first applications of the technology was to create resistance to viruses

Resistant

Susceptible

Bacterial blight (Xanthomonas sp.)

Super elongation disease (fungal)Resistant Susceptible




The use of resistant varieties

Helping the plant defend itself

Helping the plant defend to itselfA cassava plant originated from a healthy and physiologically sound cutting will not need much support to defend itself. However, some practices are recommendable: Crop rotations are always a smart

approach to prevent building up of the inoculumFields with adequate drainage prevent root rotsAdequate fertilization will produce a vigorous plant that will withstand most biotic problemsAdequate management of weeds also contributes to a healthy cassava crop

We have a great opportunity to make a difference in cassava’s future. However,we must act with responsibility and react fast when a problem arises

You are not alone ! Look for help if there is a problem.

Thank you for your attention

Contacts:[email protected]@cgiar.org

2013. ceballos. cassava diseases

Science