Influence of Seed Health on the Germination Quality of Seeds Valerie Cockerell ISTA Germination Seminar 13 June 2011, Zurich
Influence of seed health on germination: Outline Seed Health Disease transmission Seed germination Test methods Seedling Assessment Results and reporting Seed treatment/disinfection Influence on germination Results interpretation Summary
Introduction Seed Health Definition: ISTA Rules Chapter 7, 7.2.1 Seed Health Health of seed refers primarily to the presence or absence of disease-causing organisms, such as fungi, bacteria and viruses, and animal pests, including nematodes and insects, but physiological conditions such as trace element deficiency may be involved.
Seed health: disease causing organisms (1) Some seed-borne pathogens attack developing seedlings so that germination and plant establishment are reduced.
Seed health: disease causing organisms (2) Examples: Fungi Microdochium spp. Fusarium spp. Alternaria spp. Colletotricum spp. Ascochyta spp. Phoma betae cereals and some grasses maize, wheat, barley, peas. brassicas, linseed beans, linseed peas, chick pea beet
Seed health: disease causing organisms (3) Bacteria Curtobacterium flaccumfaciens pv flaccumfaciens Beans Physiological conditions Manganese deficiency (Marsh spot) Hollow heart Peas, beans Peas Pests Bruchid beetles, weavils Beans, cereals
Seed-borne Pathogens Necrotrophs: Kill host cells quickly and live saprophytically on dead tissue Present on surface of seed or within seed coat tissue Infect shoots and or roots of germinating seedlings Transmission is made by contact
Epigeal Epigeal germination favours transmission of pathogens to the cotyledons Contact of cotyledons with the affected seed coat (seed coat may remain attached or fall) fallen seed coats may affect hypocotyl if contact made
Hypogeal Hypogeal germination aids transmission of pathogens that cause foot and root rots Plumule infection result from contact with diseased seed which remain below ground during germination Invasion can occur via seed attachment into hypocotyl of plants causing foot and stem rotting In cereals direct penetration of base of coleoptile from mycelium in pericarp
Environmental factors affecting transmission: Temperature In temperate areas cool conditions encourage seedling attack. Low temperatures result in slow germination higher transmission of disease. (hypogeal germination increased contact time with infected seed) In hotter climates lower rather than higher temperatures may restrict transmission. (Fusarium spp.)
% Seedling loss Effect of Microdochium spp. infection in cereals on two sowing dates, Edinburgh, Spring 2008 50 40 1st sowing 2nd sowing 30 20 10 0-10 -20 17 18 11 22 23 24 19 20 21 Nil 31%Mn 34%Mn 40%Mn 41%Mn 58%M 11%Mn 36%Mn 31%Mn Wheat Barley n Oats -30
Environmental factors affecting transmission: Moisture Important for transmission of seed-borne bacteria. (P. syringae pv. pisi increased from 0.75% to 23.3% in compost as moisture increased from 15% to 29%, Roberts, 1992) Particularly important for aerial parts of germinating seeds, moisture levels can increase disease. In epigeal emergence, the cotyledon sometimes emerges with the seed coat or the remains of it still attached. Further transmission affected by climatic conditions. (Septoria apiicola,celery and Anthracnose, phaseolus beans)
Germination Test v Seed Health Test Seed Health test Temperature Moisture Light Germination Test Temperature Moisture/Humidity Light Top paper Between paper (BP) Grow out test (BP: ISTA Method 7-006 Colletotrichum lindumethium) Top paper Between paper Pleated paper Sand, OMG
Influence of seed health on germination: Seed Analyst Test conditions Cold pre-treatment to break dormancy encourages Microdochium spp. in infected winter wheat. Alternatives: change dormancy breaking treatment Oven Gibberelic acid
Test conditions Cold pre-treatment of linseed reduced Alternaria infection.
First count radish Second count might look like this!
Saprophytic growth 20-30 C High humidity
Peas infected with Fusarium and Botrytis sp.
Assessing diseased seedlings Normal seedlings Intact, healthy Slight defects Seedlings affected by secondary infection otherwise ok Abnormal Decayed essential structures so diseased or decayed as a result of primary infection normal development is prevented
Crambe with necrotic spotting Superficial necrotic spotting on hypocotyl
Barley seedlings infected with Cochliobolus sativus
Normal and abnormal linseed seedlings
Linseed >50% cotyledon damage
Triticum aestivum seeds infected with Microdochium spp.
Oat seedling infected with Drechslera avenae
Bean with Bruchid beetle damage
Marsh spot field beans
Seed producer/grower Question: Is my seed capable of germinating and establishing in the field, greenhouse, or polytunnel? Seed Health Test Germination Test
Germination Test: Reporting Results Symptoms of disease can be seen in the germination test. Symptoms not usually sufficient for the determination of the pathogen or accurate estimate. Gives an indication of potential disease problems. Suggest seed health test. Germination conditions may encourage saprophytic growth that are not a problem in the field. Disease leads to variability within replicates and between tests Variability dependant on pathogen or test conditions. Method chosen can reduce the affect of disease.
Disinfection ISTA Rules allow for disinfection of Beta vulgaris and Arachis hypoaea. 1983 Rules proposal put forward because of variability between laboratories in PT and CT tests. Phoma betae common contaminant in traded seed. Secondary infection a big problem.
Winter wheat with and without seed treatment
Germination test results of 38 samples of Microdochium infected wheat with a variety of treatments. % samples 85% and above. Untreated 25% Organomercury 97% Triadimenol +fuberadazole 92% Guazatine 97% Thiabendazole + carboxin 83% Thiabendazole + flutriafol 34%
Summary Seed health influences seed germination both in the field and in the germination test. Understanding the conditions which exacerbate the effect of seed-borne pathogens on germination, help with choice of method. Retest in OGM creates a barrier or simply increasing spacing can reduce effects of secondary infection. Retest when diseased abnormal greater than 4%? Disinfection, introduce more variability?
Thank you to OSTS and SASA Staff. Preparation of samples, photography and useful comment! Frances Allan Jean Smith Stuart Grieg Gillian McLaren Also thanks: To the audience for listening!