ProMED-mail is a program of the
International Society for Infectious Diseases
Date: Sun 15 Mar 2020
Source: Henan Provincial Government [in Chinese, machine trans., summ. Mod.DHA, edited]
An unusually high incidence of both stripe rust and scab of wheat crops is being reported. Areas of particular concern that are mentioned are in the provinces of Henan, Guangdong, Gansu, Anhui, the southern coastal Nanyang region, and the Hanshui River Basin.
Large amounts of pathogen inoculum, global temperature rise, susceptibility of planted wheat varieties to the fungi, and higher than usual rainfall are listed as contributing factors leading to a current epidemic of wheat stripe rust and scab.
It is stressed that control of wheat diseases and pests is at a critical stage.
Stripe rust (also called yellow rust) of cereals is caused by the fungus _Puccinia striiformis_. The disease affects wheat (_Triticum aestivum_), durum wheat (_T. turgidum_), some barley varieties, triticale (wheat/rye hybrids) and a number of wild grasses. It causes yellow stripes on leaves, which leads to loss of photosynthetic ability and plant vigour as well as stunting of plants. Yield losses of 40-100 percent have been reported in wheat.
Spores are wind dispersed in several cycles during the cropping season. Grasses and volunteer crop plants may generate a "green bridge", providing inoculum for the next crop cycle. Disease monitoring is important so that timely action can be taken to limit the spread of the pathogen as well as a build-up of inoculum. Disease management may include the use of resistant varieties, fungicide applications, and control of pathogen reservoirs. Monitoring and resistance breeding programmes have been established in different regions for early detection of new rust strains and to attempt to stay ahead of pathogen evolution.
While stem rust (_P. graminis_) poses a huge potential threat to world wheat production, stripe rust is currently causing the most damage to wheat crops on a global scale. New strains of both rusts with increased virulence and additional fungicide resistances have been reported in recent years from wheat-growing areas worldwide. Climate warming allowing survival of wheat rusts on green bridges into higher latitudes is another example of pathogens extending their range due to climate change (see also ProMED-mail posts 20141024.2895414, 20120809.1235745, 20090914.3230, and 20110718.2172). Projects for double-resistance breeding to manage both stripe and stem rusts simultaneously are in progress (see ProMED-mail post 20120831.1274190).
Stripe rust outbreaks are currently also being reported from India (ProMED-mail post 20200204.6950281 & link below) and Pakistan (see link below), an alert has been issued in the US for the eastern Pacific Northwest (see link below).
Fusarium head blight
Fusarium head blight (FHB; also called ear blight, scab) of small grain cereal crops (wheat, barley, rye, oats, maize) is caused by several fungal species originally classed into the genus _Fusarium_. FHB causes yield losses of up to 45 percent and reduces the grade of harvested grain. The fungi can also cause foot rot and seedling blight and form a complex of diseases on seeds, seedlings and adult plants. Current names of the fungi include _Fusarium graminearum_ (synonym _Gibberella zeae_), _Fusarium poae_, _Microdochium nivale_ (synonyms _Fusarium nivale_, _Monographella nivalis_), and _Microdochium majus_. The pathogens are favoured by humid conditions.
Depending on fungal strains involved and environmental factors during plant growth and grain storage, infection may also contaminate the grain with fungal toxins. The total crop may be lost because of toxin levels. The fungi persist and multiply on infected crop residues; spores are spread by wind, water, mechanical means, and with infected plant material (including seeds). For seedling blights, the main pathogen source is contaminated seed. Disease management includes fungicides as crop sprays or seed treatments, long crop rotations with non-hosts, and planting of cereal varieties with reduced susceptibility. Use of certified clean seeds is essential.
New fungal strains are emerging worldwide. Examples are the re-emergence of some fusarium diseases thought to be driven mainly by changes to climate and agronomic practices in the UK (ProMED-mail post 20100726.2497) and new FHB strains with increased mycotoxin levels in Canada (ProMED-mail post 20091210.4211). Continuing breeding programmes for new FHB resistant (or tolerant) crop varieties are needed to stay ahead of pathogen evolution.
Stripe rust symptoms on wheat:
Stripe rust on barley:
Ryegrass with stripe rust:
Fusarium head blight (FHB) on cereals: