List of Seed borne disease

List of Seed borne Diseases: When a pathogen is carried in, on, or with the seed, it is known as a seed-borne pathogen. And the disease caused by it is a seed-born disease.

Depending upon the mode of primary initiation of the infection, the plant diseases are divided into

1. Seed-borne diseases
2. Soil-borne diseases
3. Air-borne diseases

• It should be noted that an organism may be seed-borne yet not seed-transmitted because the establishment of infection in seedlings and in adult plants is the last decisive link in the process of seed transmission.
• Moreover, developing a seed-borne disease is a complicated process resulting from the interaction of pathogens, saprophytes in the soil, and leachates produced by the seeds at sowing.
• Gloeotinia temulenta, the causal agent of blind seed disease in Lolium perenne Linn., is transmitted via mycelium on seed surfaces, not through macroconidia. This is due to mycelium’s 2-year viability, while macroconidia only survive around 2 months.

Under the term seed-borne, normally all diseases transmitted by true seeds or by vegetative reproductive bodies are included. The pathogen may be present on the surface of the seed or inside the seed or maybe loosely mixed with seeds.

Causes of Seed-Borne Diseases

Different types of pathogens can infect seeds, including fungi, bacteria, and viruses. These 3 types of associations of the pathogen with seeds are termed differently:

• INFESTED – When the pathogen is present on the surface of the seed.
• INFECTED – When the pathogen is present inside the seed.
• ADMIXTURE – When the pathogen is loosely mixed with seeds in the form of bodies like Sclerotia or galls. It is known as a Concomitant Contaminant.

Classification of Seed-borne Pathogens or List of Seed borne diseases

A. Externally seed-borne pathogen

The pathogen is located on the surface of the seed mostly in the form of conidia or any other resting spore eg., Tilletia sp. Causing the bunt of wheat and Sphacelotheca reiliana Kuehn client. Causing head smut of sorghum is present as chlamydospores

B. Internally seed-borne pathogen

The pathogen may be present anywhere inside the seed, in the seed coat, endosperm, or embryo. Eg: loose smut of wheat

Seed-coat: The surface of the seed-coat is the common site of infection for most of the seed-transmitted fungi. Like

Altemaria brassicicola (Schw,) Wiltshire to Brassica

Alteraria raphani Groves & Skolko in radish

Endosperm: In maize seed, the mycelium of Diplodia zeae (Schw.) Lev is present in the endosperm. Similarly, the mycelium of Fusarium moniliforme Scheldon has been found in the endosperm of sorghum.

Embryo: Within the embryo, the pathogen may be present in cotyledons or scutellum, plumule, and radicle depending upon its nature. Sclerophthora rayssiae var. zeae are frequently present in the upper part of the plumule in maize embryos. The pathogen causes downy mildew in maize.

Concomitant seed contaminations: Some pathogens produce structures known as sclerotia, nematode galls, etc. The sclerotia and nematode galls get mixed with the seeds and are carried from one place to another along with the seeds, spreading diseases in the new areas.

Sclerotia of Claviceps purpurea (Fr.) Tul gets mixed in the seeds of rye of Bajra.

Cysts of Heterodera glycines (Ichinohe) in soybean.

Galls of Anguina tritici (steinbunch) Chitwood in wheat.

Method for detecting seed-borne disease pathogens

• Visual examination
• Water agar method
• Standard blotter method
• Growing on test
• Examination of Seed washing
• Embryo Count method
• detection of viruses: ELISA
• Molecular method: PCR

List of Seed born Diseases of some important crops, Causal organisms, symptoms, and management.

Crop	Causal organisms	Symptom	Control
Loose smut of Wheat	Utilago tritici	Ears are transformed into black powdery mass	Ears are transformed into a black powdery mass
Karnal bunt of wheat	Neovossia indica	Neovossia India	Grains turn partially into a black powdery mass of spores
Ear cockle of Wheat	Anguina tritici	Bacterial blight rice	If the seed is contaminated with galls, the galls should be removed by immersing the seeds in a 5% salt solution. The seed should be thoroughly washed in water, dried, and treated with thiram at 0.25%.
Black point of wheat	Alernaria tenuis	The seeds appear dark in color and have brown to black discoloration on the seed just over the point where embryo is	Wrinkling, rolling, and distortion of young leaves, small, raised, rounded areas or galls appear
Brown spot of rice	Helminthosporium oryzae	Brown, circular sport appears on leaves also brown sport can be seen which later enlarges and becomes ellipsoidal, oval, or circular.	Use of disease-resistant seeds
Rice Bunt	Neovossia horrida	The kernels may partially or wholly convert into a black powdery mass.	Escape disease through the sowing of late-maturity varieties. And the use of resistant variety.
Bacterial blight r ice	Xanthomonas oryzae	Complete drying of seedlings in the nursery or appearance of ash-coloured drying on leaves, which starts, from the tops	Soaking of seed for 8 hr in 0.1% cersan wet + streptocycline at 300 mg in 12 liters of water.
Ear rot of maize	Cephalosporium acremonium	White fluffy mycelia on the surface of the ear. Seeds may have white streaks which are significant on the lower half of the seeds.	Seed treatment with bavistin or thiram at 0.25%.
Grain smut of sorghum or cover smut of sorghum	Sphacelotheca sorghi	Large, cylindrical, cone-shaped smut galls on ears, black powdery mass on ears	Treat the seed with 1.0% organomercurial fungicide at 0.25%
Kernel smut of sorghum or Sorghum Ergot	Sphacelia sorghi	Honey dew like drops on spikelets and sclerotia in the ear head	Honey dew-like drops on spikelets and sclerotia in the ear head
Downy mildew or green ear disease	Sclerospora graminicola	Spikelets get transformed into leafy structures which are twisted in appearance. The ears are malformed. The affected plants are stunted and pale yellow.	Seed treatment which is metalaxyl at 6g/kg seed and spray plant after 40 days of emergence at 0.2%.
Ergot of bajra	Claviceps fusiformis	The appearance of a sticky substance on the spikelet. Presence of sclerotial in the ear head	Remove the sclerotia by treating the seed in 10% salt solution. Wash, dry, and treat the seed with 0.25% thiram
Late blight of potato	Phytophthora infestans	Purplish-black lesions on leaves. The disease spreads to haulms and then to tubers. Affected tubers have brown lesions inside	Use of a resistant variety
Purple stain of soybean	Cercospora kikuchii	Pink, light, or dark purple spots on the seed. Cracks may be seen in the spotted area	Seed treatment with thiram + bavistin (1:1) at 0.4% may reduce the seed-borne inoculum.

Control of Seed-borne Diseases

The seed-borne diseases can be controlled by the following methods.

Physical treatment:

It includes hot-water treatment and solar-heat treatment.

Hot-water treatment

Seeds are soaked overnight in water and then placed in hot water at 52°-54°C for about 20-30 minutes. Seeds should be dried before storing.

Solar-heat treatment

Seeds are soaked in water for about 4-6 hours, preferably in the early morning, and then spread in a single layer on a cemented floor. The treatment should be done on a bright sunny day. The treatment is very effective against loose smut of wheat if it is done during May-June in northern parts of India.

Chemical treatment

It requires the use of fungicides, bactericides, or even antibiotics. Chemical treatment of seeds is normally done as

• Dry or dust treatment
• Slurry treatment, in which the chemical is mixed with the liquid to make a slurry and applied to the seed
• Liquid treatment, in which a concentrated liquid solution is applied directly to the seed.
• Spray treatment, in which the slurry or liquid is sprayed onto the seed
• Mist treatment, in which seeds are exposed to the mist created from liquid or slurry.

The following machines are generally used for applying chemicals to seeds

Rotary seed treater: A known quantity of chemical is mixed with a known quantity of seed and is rotated in a drum for 15-20 minutes.

Slurry seed treater: A fixed quantity of chemical solution is dropped every time in a fixed quantity of seed and the same is thoroughly coated around seeds.

Mistomatic seed treater: A fixed quantity of chemical solution falls on a fast-rotating cone which breaks it into very small droplets that get adhered to the seed surface. This is an effective and economical way of seed treatment.

Importance of addressing seed-borne diseases:

Seed-borne diseases have a serious impact on agriculture, food security, and the economy.

Path of Seed borne infections

• Infestation of seed may during harvesting and processing.
• Through pollen tube
• Infection via flower or fruit

Impact of Seed-Borne Diseases

• Effects on crop yield and quality
• Economic implications for farmers and the agriculture industry
• Potential for spread and epidemic outbreaks
• Threat to global food security
• Trade Barriers: Seed-borne diseases can create barriers to international trade.
• Biodiversity Loss: Seed-borne diseases can lead to the loss of plant biodiversity.

Preventing Seed-Borne Diseases

• Quality assurance in seed production: healthy seeds through seed certification and during production.
• Sanitation measures in seed production plots
• Seed certification of seeds
• Seed treatment: various methods to treat seeds and eliminate pathogens like acid treatment, and heat treatment.
• Breeding for disease resistance

Also, check out Types of seed dormancy, Seed pelleting