Cassava is the second most important crop staple in East and Central Africa after maize, providing food security to hundreds of millions of rural and urban households. Successive virus disease pandemics, however, have resulted in losses worth hundreds of millions of dollars each year, threatening the livelihoods of all those who depend on this source of calories. IITA has partnered with national research programs in the region to identify and promote varieties resistant to cassava mosaic virus (CMV), but this was curtailed by viruses causing cassava brown streak disease (CBSD), to which these varieties did not have resistance.
Recently, however, conventional, and marker-assisted breeding have been used to develop several varieties with good levels of resistance to both viral diseases. But some obvious and perennial challenges remain. Firstly, cassava is a clonally propagated crop with a low multiplication ratio, which means that it can take many years before a new variety becomes readily accessible to farmers.
Secondly, it is difficult to maintain the health of planting material over multiple cropping cycles in heavily infected production zones. The first challenge is being overcome using improved methods for rapid propagation. Systems for the screenhouse-based multiplication of virus-tested cassava plantlets derived from tissue culture have been established in several countries in East Africa. Most recently, the semi-autotrophic hydroponics (SAH) technology has been introduced to eastern Democratic Republic of Congo (DRC), Rwanda, and Tanzania. This allows for the multiplication of more than 200,000 SAH plantlets in a year from starting material of just 100 tissue culture plants, with SAH plantlets planted directly into an irrigated field. Arguably, the greater challenge facing cassava seed systems in East Africa, is protecting plant health from early generation seed up to the level of seed production within rural farming communities.
Pathogens causing diseases are easily spread from one generation of cassava plants to the next, as farmers use cuttings from parent plants to establish a new crop. This problem is particularly acute in East Africa, where the viruses causing CMD and CBSD are prevalent. The first step in overcoming this problem is to obtain source material from tissue culture, which ensures virus-free plantlets .
The first efforts to establish ‘clean’ fields of cassava planting material of improved varieties were undertaken in 2011 at Kunga, Tanga Region, north-eastern Tanzania. Cuttings from screenhouse-hardened virus-indexed tissue culture plantlets of variety Kiroba were obtained from the Tanzania Agricultural Research Institute’s (TARI) Kibaha research station. The Kunga site was isolated from other cassava fields and had very low vector and virus disease pressure due to its location in the Usambara Mountains. Unfortunately, the site proved too cool for vigorous cassava growth, and in 2012 the materials were moved to an isolated lower altitude farm at Mwele, near Tanga. Over a period of several seasons, and by applying measures to ensure that whiteflies were controlled, and virus-infected plants were removed, it was demonstrated that it was possible to maintain cassava planting material that is virus-free.
From 2012 onwards, IITA worked closely with the Tanzania Official Seed Certification Institute (TOSCI) to draft, validate, and publish guidelines for certifying cassava ‘seed’ at pre-basic, basic, and certified levels. These were formally gazetted and appended to the Seed Act in January 2017. Guidelines for quality declared seed (QDS), produced at community level, were added in April 2020. Capacity of TOSCI seed inspectors to implement the new quality assurance system was strengthened through training workshops. Furthermore, the capability of TOSCI to conduct the required virus tests for pre-basic cassava planting material was enhanced by designing testing protocols, training lab technicians, and providing key pieces of lab equipment to TOSCI’s HQ in Morogoro. The sustainability of this system was improved through TOSCI’s revision of its fee structure for inspections and lab testing, which was incorporated into guidelines appended to the Seed Act in 2017.
A system for certifying the quality of any seed can only exist within a sustainable and commercial seed system. To achieve this, IITA partnered with TARI, TOSCI, and the Mennonite Economic Development Associates (MEDA) in running a Bill & Melinda Gates Foundation-funded project called Building an Economically-Sustainable Seed System in Tanzania for Cassava (BEST-Cassava). One of the project’s key achievements has been the establishment of a country-wide network of >400 cassava seed entrepreneurs (CSEs). These seed producers operate at all levels of the system, from pre-basic to QDS, and have been trained in ‘clean’ seed production, business models, and marketing by the MEDA team.
Efficiency and responsiveness of the seed certification system delivered by TOSCI have been enhanced through the incorporation of IITA’s SeedTracker e-certification platform. TOSCI officers are now routinely using this system for registration and certification of CSEs. CSEs themselves also benefit from the opportunity to market their seed more widely, as anyone accessing the www.seedtracker.org website can see the locations of all registered cassava seed producers in Tanzania. Finally, TOSCI has led the training of extension officers who will take on the role of Authorized Seed Inspectors (ASIs). This is greatly extending the coverage of the cassava seed quality assurance system in Tanzania and making it simpler and cheaper for QDS producers to get certified and thereby grow their businesses.
The success in meeting the high-quality seed needs of tens of thousands of cassava growers in Tanzania has encouraged the implementation of similar initiatives in Burundi, Rwanda, and eastern DRC. As new opportunities arise for the production and marketing of both fresh and processed cassava products, the modernized quality-assured seed systems being developed are set to make a major contribution to the transformation of African agriculture.
Authors: James Legg, IITA-Tanzania (Dar es Salaam), Latifa Mrisho, IITA-Tanzania (Dar es Salaam) and University of Dar es Salaam,
Neema Mbilinyi, IITA-Tanzania (Dar es Salaam), Annalyse Kehs, Peter McCloskey, and David Hughes, Penn State University, USA