Wheat is one of the most important global food crops for humans, but one of the deadliest wheat diseases is the stem rust. However, scientists have bred stem rust resistant varieties for farmer adoption.
Wheat, also known by its scientific name Triticum aestivum L. is the most widely cultivated cereal grain worldwide, providing approximately 20 percent of global calories to humans, but it has a challenge of pest and disease burden. One of the major diseases include Fusarium head blight, a wheat infection caused by Fusarium spp. Scientists dealing in wheat breeding in the country say Fusarium head blight is a major challenge of wheat across the globe, but the current wheat breeding initiative is addressing it. One of the deadliest wheat diseases is the stem rust but scientists have bred varieties which are resistant, for farmer adoption.
Background
Wheat was first introduced to Uganda in 1912, grown on the slopes of the Mount Rwenzori. Historically, it was grown in high-altitude areas, including the slopes of Mountains Elgon, Rwenzori and Muhavura. Over time, production has expanded to districts like Kapchorwa, Kabale and Kasese, but it remains low, with local production meeting only a small fraction of around four percent of the nation's demand. A growing population and increased urbanisation in Uganda, like in other parts of Sub-Saharan Africa, have led to a rise in the demand for wheat-based foods like bread, pasta, and noodles.
Uganda faces challenges such as drought, heat and poor soil fertility, which hinder productivity in rain-fed environments.
However, scientists from the National Crops Resources Research Institute (NaCRRI) are actively involved in breeding and adopting new drought-tolerant and disease resistant varieties for local farmers. Ugandan researchers collaborate with international centres like International Maize and Wheat Improvement Centre (CIMMYT) and the International Centre for Agricultural Research in the Dry Areas (ICARDA) to access improved wheat germplasm and breeding technologies.
Wheat disease and breeding initiatives
Daniel Bormet Kwemoi, a wheat breeder at NaCCRI, explains that many farmers in Uganda are growing wheat in high altitude areas such as Kapchorwa, Kabale, Kisoro, Zombo, Buhweju and Insingiro. These farmers have been experiencing wheat diseases such as stem rust, also referred to as UG99, yellow rust and strip rust, which mainly thrive in cold areas, leading to loss of yield. However, with the is breeding varieties which are also resistant to wheat Fusarium head blight.
This is because farmers in Uganda are at risk of this disease as it is already in farmer fields in Morocco, Sudan and Egypt. In major wheat growing areas, it is already a big challenge.
There is an ongoing breeding programme by NaCRRI scientists, who are now at field trial stage focusing on heat stress tolerance as well as disease resistance.
The team has undertaken tests in eight agro ecological zones and has so far selected 40 production lines out of the 300 lines. They are in the second phase of the trials and they are testing for disease resistance, baking qualities and heat tolerance, among others. This will lead them to come up with four varieties, which will be released for farmer adoption. What farmers are growing right now are Naro I, II and III, which are resistant to yellow rust, leaf rust and UG99 and are high yielding.
Fuzarium head blight burden in Africa and efforts to curb it
Wheat production on the African continent, including Uganda, has been constrained by factors such as diseases, insect pests, variable climate conditions and competition from other crops. One of the diseases is Fusarium head blight, which is a pre-harvest disease, although Fusarium spp. can grow post-harvest if wet grains are not dried effectively. In the field, the disease is characterised by premature bleaching of the infected head shoots of the plant, and formation of orange spore bearing at the base of the leaves which protects the shoot.
This leads to reduction in grain yield due to reduced seed weight because the kernels will shrivel as a result of the disease infection. A team of scientists from Kenya led by John Maina Wagacha analyses the types of the disease as below: The major Fusarium spp. associated with FHB worldwide include: F. graminearum, F. poae, F. avenaceaum and F. culmorum. However, F. graminearum, F. poae, F. avenaceaum, F. chlamydosporum and F. culmorum are the major Fusarium spp. associated with the disease in Africa.
Most Fusarium spp. produce inocula and are most pathogenic to wheat heads at warm temperatures and humid climate.
Once the shooting head of the wheat plant is infested with the disease, it produces toxins which destroys the seed. Extended periods of greater than 90 percent relative humidity and 15-30 degrees Celsius temperature create suitable conditions for infection. Continued wet conditions after flowering may increase the potential of the spores to be blown by wind or rain-splashed to nearby ears.
How global scientists are preserving traditional varieties for breeding initiatives
Fusarium head blight being a major challenge as one of the wheat diseases across the globe has led scientists to collect traditional land races whose genes can be used for disease resistance. Dr Simon Grifiths from John Innes Centre explains that his team, in collaboration with scientists from China, have collected land races and are breeding wheat varieties with resistance against wheat diseases, including Fusarium head blight.
In a publication on the China Global Television Network, it is stated that a collaborative study led by scientists from China and Britain revealed that at least 60 percent of the genetic diversity found in a historic collection of wheat is unused, providing an unprecedented opportunity to improve modern wheat breeding and achieve food security. The study, jointly conducted by a research team from the Agricultural Genomics Institute in Shenzhen under the Chinese Academy of Agricultural Sciences, the John Innes Centre in Britain and other research organisations, was published in the latest issue of the academic journal, Nature.
Faced with a series of challenges such as the continuous growth of global population, complex climate change and the gradual slowing down of the cultivation of new wheat varieties, scientists urgently need to find efficient and precise methods for wheat breeding to cultivate high-yield and high-quality new varieties.
Experiments have been carried out across China, and a comparative analysis of the nearly century-old wheat with modern wheat varieties has been conducted.
Using modern technologies such as genomics, genetics, bioinformatics and molecular biology, scientists built a wheat genomic variation map and revealed that modern wheat varieties have lost more than 60 percent of their genetic diversity through long-term artificial selection. Dr Griffiths notes that the missing 60 percent discovered in the study is full of beneficial genes, which scientists are considering in their breeding programme to feed people sustainably
The team is optimistic that the functional and beneficial diversity that were lost in modern wheat varieties can be added into elite varieties in the breeding programmes. The research team also discovered new genes and thousands of genetic variation sites in wheat for high yield, high calcium content, resistance, efficient nitrogen use and resistance to blast and leaf spot diseases.
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