New complex diseases threaten tobacco
RESEARCH firm Kutsaga has recorded increased incidences of wilting in the tobacco crop in the current farming season amid an outbreak of new complex diseases, putting production of one of Zimbabwe’s largest forex earners under threat.
In its latest report, Kutsaga said diagnoses on plants submitted for testing had shown that most of the wilts were being caused by co-infections of fusarium spp and phytophthora spp resulting in a fusarium wilt or black shank (FW/BS) disease complex.
“This phenomenon has been widely observed in the 2023/24 farming season, but isolated cases have been reported since the 2018-19 season,” the report read in part.“For example, in the 2019/20 farming season, there were 15 recorded cases; then in 2021/22, there were five recorded cases. The number of recorded and reported cases has risen astronomically to more than 40 this season.”
While the FW/BS disease complex is a recent phenomenon in Zimbabwe, Kutsaga said it was one of several complex diseases threatening tobacco production in other tobacco growing countries such as the United States (US) and China.
“It was anticipated that climate change would pose certain challenges in agriculture, including a change in the status of pests and diseases,” said the research institution.“Indeed, following the extremely hot and dry conditions experienced in Zimbabwe this agricultural season, certain pests and diseases, previously considered not economically important on tobacco have become prominent.”
Fusarium wilt of tobacco is a widespread disease that occurs in many countries. It was first reported in the US in 1916. By the 1990s, it had become the most notorious and damaging disease of cigar wrapper tobacco in Connecticut and Massachusetts, affecting approximately 20% of tobacco production fields and causing severe yield losses. It is present in all countries on the American continent and is widespread in Asia and Oceania.
In Africa, fusarium wilt is particularly severe in Malawi, and until recently, it was of minor importance in Zimbabwe. Fusarium wilt symptoms start as vein-clearing on the younger leaves with simultaneous drooping of the older lower leaves.
This is followed by stunting, yellowing of the lower leaves, defoliation, marginal necrosis and plant death. Sometimes, the wilting and yellowing symptoms appear on one side of the plant.
The disease can cause significant damage under high temperature and humid conditions. Several fusarium spp causes wilting and root rots in tobacco. Previously, Kutsaga said fusarium oxysporum f.sp. nicotianae was the predominant disease in tobacco.
However, in recent Kutsaga studies, the highly virulent generalist pathogen fusarium falciforme and fusarium foetens were also detected in samples collected countrywide and are now among the pathogens causing fusarium wilt in Zimbabwe.
Both F. falciforme and F. foetens have also been detected on potatoes in the country. “Thus, there is high likelihood that these fusarium wilt pathogens could spread and infect other key food and cash crops thereby threatening the profitability and sustainability of the agricultural sector in the country,” Kutsaga said.
“Research is underway at Kutsaga to understand the dynamics of this new disease complex.”With the inclement weather being experienced and ongoing climate change, Kutsaga urged farms to be on the lookout for changes in disease and pest profiles on crops, and how they can impact tobacco.
“Growers are encouraged to report any atypical behaviour in pests, diseases or varieties on the various communication platforms offered by Kutsaga so that appropriate advice can be given,” Kutsaga added.
-newsday
