What is Sugarcane Mosaic Virus?

Discover Sugarcane Mosaic Virus

Sugarcane mosaic virus (SCMV) is a plant disease belonging to the Potyviridae family that poses serious challenges in Florida turfgrass environments.

Investigators could not infect plants experimentally with this sugarcane mosaic disease for years until Kamerling 193 believed it to be contagious and used juice derived from infected sugarcane to inoculate plants with diseased sugarcane juice.

What Is It?

Sugarcane mosaic virus (SCMV), one of the major plant diseases afflicting sugarcane, results from either single or combined infections of three viruses: Sugarcane Mottle Virus (SCMV), Sorghum Dwarf Mosaic Virus (SrMV) and Sugarcane Streak Mosaic Virus (SCSMV).

The sugarcane mosaic virus causes poor-quality cane with less sucrose. This has a big effect on production costs and economic losses. Mosaic disease in sugarcane can be detected through visual inspection and PCR testing of leaves without symptoms. Visual inspection requires professional knowledge, skill, and the ability to recognize mosaic symptoms quickly while testing by PCR identifies specific strains of the virus responsible.

PCR testing of symptomless leaves provides more accurate and detailed information regarding virus presence than visual inspection, although it is more expensive and labor-intensive than its visual equivalent. Furthermore, sugarcane can challenge this testing method due to genetic segregation within its hybrid seed crop and the multiple resistance genes present.

Studies have demonstrated that planting virus-free cultivars can significantly decrease incidences of mosaic disease in sugarcane and increase sucrose content and yield.

Resistant varieties offer the most practical and cost-effective means of mitigating the impact of mosaic disease on sugarcane production. A recent metagenomics study demonstrated that SCMV had not been found in commercial sugarcane plantings during these years (Filloux et al., 2018). However, severe outbreaks have occurred since 2013 in St Augustine grass (cultivar Floratam) and annual grain crops and grasses like sorghum in the EAA.

The emergence of SCMV-causing strains poses a grave threat to future sugarcane production, so all known hosts of SCMV must remain away from sugarcane fields, particularly those known to harbor SCMV strains, through proper weed management practices.

Symptoms

Mosaic Disease, caused by a plant virus, manifests similarly to other plant ailments like nutritional deficiencies. Signs may appear on either leaves or stems of affected plants and, depending on their severity, may even result in their death.

Mosic disease can cause significant yield losses in sugarcane, sorghum, annual grasses, and turfgrass.

The symptoms include:

• Green stripes on the paler green to yellow chlorotic areas with yellow stripes or streaks;

• Usually developing on foliage;

• Sometimes leading to leaf necrosis, defoliation, reduced growth, wilting, or stunting of plants.

This virus can be spread by weeds, infected seeds, or even the wind and can have disastrous effects on harvest product quality. Symptoms may mimic those caused by nutritional deficiencies; intensity and appearance depend on the season and environmental conditions.

In Kharif 1966, a devastating mosaic disease hit finger millet crops in Southern Karnataka and border districts of Andhra Pradesh in India, leading to their abandonment. The infection was caused by a potyvirus later known as sugarcane mosaic virus, Sorghum Red Stripe Virus (SCRSV), and Sorghum Rhizome Mosaic Virus; with high transmission potential and infected plants highly vulnerable to other members of its family (Subbayya & Raychaudhuri, 1970).

St. Augustinegrass has shown some resistance to SCMV; however, this disease remains highly prevalent in sugarcane-producing areas of central Florida and is an acute threat for growers in these regions due to its negative effect on sugarcane production as well as symptomatic turfgrass in fields nearby.

Researchers in India conducted research that demonstrated S. robustum genotypes to have resistance to SCMV and SrMV due to having lower levels of the SCSMV plasmid that causes symptoms. A 0-6 scale mosaic phenotyping technique developed here will be useful for screening Saccharum germplasm collections against mosaic virus and identifying resistant genotypes.

Prevention

Florida gardeners are alarmed about the recent outbreak of sugarcane mosaic virus, as gardeners fear its possible impact on their lawns. Mosaic is caused by a virus first identified in sugarcane and now found affecting turfgrass across North, Central, and South Florida counties. Mosaic symptoms in turfgrass include dieback in its green blade and other parts of its plant with distinct blotchy and streaky patterns; symptoms often worsen in fall months.

According to the UF/TREC Plant Diagnostic Clinic, you can prevent mosaic disease from appearing in your yard in a few ways. One is planting resistant varieties known for resisting SCMV; another way is avoiding mowing lawns when wet (especially those showing symptoms) - instead, it would be wiser to mow healthy lawns before those showing mosaic symptoms; additionally, it is wise not to water or irrigate immediately following mowing, since watering may contribute to further spreading it around.

Fungicides may not be effective at treating lawn diseases, so it is wise to prevent their recurrence by not applying fertilizers with high nitrogen contents that promote grass growth - something that could become an entryway for viruses to invade and take hold. To do so, avoid fertilizers with high nitrogen levels since that will allow it to create an ideal breeding ground for viruses to flourish.

As another preventive measure hiring a professional lawn care service with experience dealing with this disease is another effective preventive strategy. These companies should have a program in place that includes regular treatments of your lawn with environmentally safe chemicals and keeping an eye out for signs of the fungus so fungicides can be applied quickly to limit potential damage.

Studies on artificial transmission of the virus have been performed extensively, with most researchers believing that when exposed to air after extraction from infected plants, extracted juice becomes much weaker or loses its capacity for producing mosaic symptoms and must, therefore, not be exposed again until inoculation takes place. Therefore, methods were devised that allow more flexibility when manipulating juice without exposing it directly to air, maintaining its infectiousness.

Treatment

The mosaic virus has long been detected in sugarcane fields around Miami, Florida; however, it appears to be spreading recently. Recently it has been seen in many fields south of 38th Avenue N near Biscayne Bay, where UF/TREC tested several turfgrass samples, and all tested positive for sugarcane mosaic virus.

Mosaic symptoms appear as blotchy and streaky patterns of green and yellow leaves caused by viruses attacking invading cells in the plant's epidermal layer. Mosaic can weaken and diminish plant vitality, eventually leading to yellowing crowns and rootstocks and the death of its host plant.

Plant virus detection can be accomplished using various methods, including indirect ELISA, RT-PCR, and molecular techniques such as RT-LAMP. While indirect ELISA remains the go-to approach for virus detection in plants, RT-PCR/RT-LAMP methods are more sensitive and can detect multiple viruses simultaneously.

Insects, wind, and human activities such as irrigation and crop harvesting can spread the Sugarcane mosaic virus. Preventing its spread requires effective insect control strategies and limiting excessive irrigation practices; alternatively, resistant varieties could help mitigate its spread.

An effective fungicide program can also aid in controlling this disease and is highly recommended. Copper sulfate, malathion, propanil, or pyrethrins may all contain active ingredients to combat the problem effectively.

Once mosaic has taken hold in your lawn, there is no cure - but homeowners can help prevent its spread with regular inspections of their yard for signs of illness and by keeping weeds and virus-susceptible turfgrasses away from it. Also, keeping soil healthy with proper fertilization and aeration will aid in keeping this virus at bay.

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