Specific Work Instructions: Inspection of Pedigreed Pulse Seed Crops
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SWI 142.1.2-3: Inspection of Pedigreed Pulse Seed Crops
Table of Contents
- 0.0 Introduction
- 1.0 Scope
- 2.0 References
- 3.0 Definitions
- 4.0 Specific Inspection Procedures
- Appendix I: Legume Flower Illustration
- Appendix II: Field Pea Descriptions and Illustrations
- Appendix III: Chickpea Descriptions and Illustrations
- Appendix IV: Field Bean Descriptions and Illustrations
- Appendix V: Lupin Descriptions and Illustrations
- Appendix VI: Lentil Descriptions and Illustrations
- Appendix VII: Fababean Description
- Appendix VII: Diseases that May Affect Plant Appearance
This version of the Pedigreed Pulse Seed Crop Inspection procedures was issued April 1, 2017.
This Seed Program Specific Work Instruction (SWI) is subject to periodic review. Amendments will be issued to ensure the SWI continues to meet current needs.
The contact for this Seed Program Specific Work Instruction (SWI) is the National Manager, Seed Section. Comments regarding the content of this document should be addressed to the National Manager at SeedSemence@inspection.gc.ca.
This Seed Program SWI is hereby approved.
Director, Plant Production Division
The most up to date version of this document will be maintained on the CFIA website. In addition, the signed original will be maintained by the National Manager, Seed Section. A copy of the latest version is available upon request to SeedSemence@inspection.gc.ca.
The purpose of pedigreed seed crop inspection is to provide an unbiased inspection and complete a Report of Seed Crop Inspection on the isolation, condition, and purity of the seed crop to support a certification decision made by the Canadian Seed Growers' Association (CSGA). It is the inspector's responsibility to describe the seed crop as observed at the time of inspection.
This Seed Program Specific Work Instruction (SWI) outlines the procedures that a seed crop inspector will follow in inspecting seed crops of field bean, chickpea, fababean, lentil, lupin, and pea for pedigreed status. The seed crop inspection program supports the CSGA determination of whether seed crops grown for pedigreed status meet the requirements for seed crop production and seed crop purity standards as established in the CSGA's Canadian Regulations and Procedures for Pedigreed Seed Crop Production (Circular 6).
The publications referred to in the development of this SWI are those identified in SPRA 101. In addition, the following were used:
- Bean Diseases and Their Control, Agriculture Canada Publication #1758, 1984;
- Sweet White Lupin: A potential crop for Ontario, Brebaum, S. and G. L. Boland, 1995, Can. J. Plant Sci., 75: 841-849;
- Alberta Agriculture, Food and Rural Development
- British Columbia Ministry of Agriculture
- Purdue University Center for New Crops and Plant Products
- Saskatchewan Ministry of Agriculture
For the purposes of this SWI the definitions given in SPRA 101 and the following apply.
- pigment ranging from red to blue to violet
- includes field and garden, white, navy, coloured or dry edible type bean
- flattening of stems
- the part between two nodes
- includes reclamation and green manure types
- place on a stem where a leaf is attached, often swollen
- includes field, pigeon, maple and forage types
- (only applicable to fababean and field pea) a plant can be considered tall when the main stem is approximately 15 cm above other main stems of the general plant population
4.0 Specific Inspection Procedures
Inspection of pedigreed seed crops of pulses should be carried out as described in SWI 142.1.1 – Pedigreed Seed Crop Inspection, with the additional conditions and information provided in the following sections.
4.1 Inspection Requirements
Inspection of pulse crops differs from other crop kinds in that the time of inspections for each kind of pulse crop varies.
- Peas (all types) - at early flower stage about 60 days after planting date.
- Lentil, chickpea, and lupin - at full flower.
- Beans (field) - at seven days after inception of flowering when flower colour can be observed. In periods of cool temperatures, inspections could be done as late as 14 days after the inception of flowering as the cool weather can delay flowering.
- Fababean - at full flower stage.
The inspection requirements for chickling vetch (grass peas) may be found in SWI 142.1.2-5 Forage, Turf, Groundcover and Native Species Pedigreed Seed Crop Inspection Procedures.
Lentil is an early maturing crop kind with harvest, under ideal conditions, beginning in early August. Seed crop inspectors should obtain the seeding date of the crop and anticipate inspection times accordingly.
The seed crop inspector should refer to Appendices I to VII for general descriptions of pulse species to assist in varietal identification.
4.2 Crop Inspection
The seed crop inspector can obtain a description of the variety (DOV) through CSGA SeedCert.
Seed crop inspectors should note the various diseases in Appendix VIII which may affect the appearance of the crop.
4.2.1 Field Peas
Peas may include commodity, forage type and specialty peas for inspection purposes. It should be noted that seed crop inspector mobility during inspection of pea seed crops may be affected by the height and density of the crop as it matures, and therefore the seed crop must be inspected at the early bloom stage.
In some exceptional cases, it may be necessary to reduce the count size for field peas to closely examine off-types that are very difficult to observe in the crop. Common off-types are leafed types in semi-leafed varieties, some of which are shorter than the norm of the variety. The procedures set out in Section 6.6 and Appendix V of SWI 142.1.1 are used in those exceptional cases when the seed crop inspector cannot do six counts of 10,000 plants each.
Seed crop inspectors must watch for potential mixtures of fern-type and unifoliate type varieties which are difficult to see.
4.3 Completing the Report of Seed Crop Inspection
The requirements for completing a Report of Seed Crop Inspection for pulse seed crop inspection are the same as those described in SWI 142.1.1 – Pedigreed Seed Crop Inspection.
Appendix I: Legume Flower Illustration
Appendix II: Field Pea Descriptions and Illustrations
Field pea (Pisum sativum) is an annual cool-season grain legume (pulse) crop. There are two main growth types of field pea. One type has normal leaves on vines that are one to two metres in length; the second type is the semi-leafless type that has modified leaflets reduced to tendrils, resulting in shorter vines of 0.75 to 1.3 metres in length. Pea normally has a single stem but can branch from nodes below the first flower.
Most varieties of pea produce white to reddish-purple flowers, which are self-pollinated. Each flower will produce a pod containing four to nine seeds. Pea varieties either have indeterminate or determinate flowering habit.
Indeterminate flowering varieties will flower for long periods and ripening can be prolonged under cool, wet conditions. Indeterminate varieties are later in maturity ranging from 90 to 100 days. Determinate varieties will flower for a set period and ripen with an earlier maturity of 80 to 90 days. Field pea is sensitive to heat stress at flowering, which can reduce pod and seed set. Indeterminate varieties are more likely to compensate for periods of hot, dry weather and are more adapted to arid regions. Determinate, semi-leafless varieties that have good harvestability are more adapted to wetter regions.
Flowering usually begins 40 to 50 days after planting. Flowering normally lasts for two to four weeks, depending on the flowering habit and weather during flowering.
- cotyledon colour
- flower colour
- leaflet presence
- maximum number of leaflets
- plant anthocyanin colouration
- plant growth type
- plant height
- pod length, width and curvature
- shape of flower standard base
- stem vine length
- stipule size
- stipule marbling
- time to maturity
The expression of stem fasciation varies considerably due to environmental conditions, although the presence or absence of fasciation is usually clear.
Stem vine length
The vine length indicated in the variety description is generally based on harvested plants at the mature green seed stage. The measurement includes nodes with scale leaves. Both plant height at flowering and stem length at the mature green seed stage may vary with site and season due to different responses to day length, temperature and soil moisture but can be used at a single site to allow the separation of different varieties.
Number of nodes
The number of nodes on a stem can vary due to flower abortion under certain environmental conditions. Nodes with scale leaves should be included in the observation.
Axil anthocyanin colouration
The colour of the axil can be reddish purple or pink in varieties with anthocyanin colouration. The assessment of the colouration of the axil should be made over the whole plant; double rings may not always be clearly defined at any one particular node. The latter is best observed on the underside of the stipules.
Maximum number of leaflets
The maximum number of leaflets per leaf should be recorded over the whole plant. The occasional plant may have a larger number of leaflets per leaf. The maximum number of leaflets per leaf for a sample of plants should be recorded and an average value calculated. Note that for semi-leafless and leafless varieties observation of this characteristic will not be relevant.
Leaf margin indentations
The observation of leaf margin indentations should be made over the whole plant, with the exception of the lowest six nodes and aerial and basal branches.
Leaf indentation degree
The observation of petiole length should only be made at the second fertile node on varieties without leaflets. The length should be recorded from the axil to the point where the first tendril occurs.
Rudimentary stipules are lanceolate and surface area is reduced significantly by up to 80%. Plants with "Rabbit-eared" stipules are not examples of rudimentary stipules.
"Rabbit-eared" stipules are parallel, rather than divergent, with pointed tips.
The observations for length and width of the stipule should be made at the second fertile node. To measure stipule size, the stipules should be detached from the plant and flattened. The width of the stipule is measured at the widest part.
The length of the peduncle should be measured from the axil to the first node or bend in the peduncle.
The observation of stipule marbling should be made over the whole plant. In order to assess, the plant should have at least eight nodes, since flecking or marbling in some varieties may not be expressed at lower nodes.
Stipule marbling density
Flower standard base shape
The observation of the shape of the base of the flower standard should be made on a sample of a minimum of 20 different plants. The standard should be detached from the flower and flattened on a hard surface for observation.
The length of the pod should be measured at the second fertile node on a sample of at least 20 plants. Pods should be fully developed or swollen. Green seed should be firm and becoming starchy.
The width of the pods at the second fertile nodes should be measured on a sample of at least 20 plants. The measurements should be taken from suture to suture on unopened pods.
The observation of pod parchment should be made on samples from different plants when the pods are dry and papery. The pod should be opened along the suture without damaging the edges of the two valves. The distribution of sclerenchyma, which makes up the parchment, may be observed by reflecting light (preferably daylight) on the inside of the pod wall.
If parchment for any pod is difficult to determine, pods from other nodes on the same plant should be examined.
Degree of pod curvature
Direction of pod curvature
Shape of distal part of pod
The observation of the shape of the distal part of the pods should be made only on varieties without a thickened pod wall. They should be made on a sample of plants and on several nodes of each plant when pods are fully developed. Care should be taken where pods are strongly curved, where the beak is longer than the pod tip, or where parchment is not entire. Some varieties have a blunt tip which is rounded, but the beak is higher up the pod.
Varieties with yellow pods may also have milky yellowish peduncles and sepals. In the presence of anthocyanin, colouration of the pods will appear pale red.
The appearance of green pods is the result of yellow, purple and blue-green colours not being expressed.
Blue-green pods are dark and slightly bluish, but not as blue as blue-green foliage. The colour develops with time and may be more accentuated in hotter, drier conditions.
The expression of purple pods can be variable and unstable, often disappearing on the same plant or being reduced in its distribution on the pod.
Strings of pod suture
The observations of the strings of the pod suture should be made on fully developed pods. If assessed when pods are not fully developed, strings of suture will be absent or partial. The strings are best observed when temperatures exceed 20°C. With cooler conditions and/or more developed pods, the strings of the suture will appear later than normal. The occurrence of less wrinkled seeds in compound starch grain types appears to be associated with the absence or reduction of the strings of the suture.
Anthocyanin colouration of pod suture
The observation of the anthocyanin colouration of the pod suture should be made on varieties known to contain anthocyanin. Observations should be made over the whole plant when pods are well developed and are beginning to dry out.
Intensity of green colour of immature seed
The observation of the intensity of the green colour of immature seeds should be made when the seed is firm, but before seeds become starchy to taste.
Seed with green cotyledons may appear creamy white before the seed is fully developed. Varieties with blue-green pods may also have very dark green seed colour.
Appendix III: Chickpea Descriptions and Illustrations
Chickpea (Cicer arietinum) is classified into "desi" or "kabuli" types based primarily on seed colour. Desi chickpea has a pigmented (tan to black) thick seed coat and small seed size along with coloured flowers. Kabuli chickpea, sometimes called "Garbanzo bean", has thin, white to cream-coloured seed coats and range in size from small to large (>100 to <50 seeds/30 g). Kabuli type chickpeas have white flowers.
Chickpea matures later than dry pea or lentil, and prefer a longer, warmer growing season. Desi chickpea flowers one day to one week earlier than kabuli types, depending on the specific varieties being compared. Large-seeded kabuli varieties generally mature one to two weeks later than desi types, but new Canadian kabuli varieties have been bred for earlier maturity. Average maturity will range from 100 to 130 days depending on the variety and the climatic conditions.
The chickpea plant is erect with primary and secondary branching, resembling a small bush. There are two leaf types, the "fern" leaf with multiple leaflets attached to a leaf stem, and the single or "unifoliate" leaf that is present on some kabuli varieties. Most varieties have fern type leaves that are about 5 cm in length with 9 to 15 leaflets. The plant flowers profusely and has an indeterminate growth habit, continuing to flower and set pods as long as climatic conditions are favourable. Chickpeas are predominately self-pollinating however, cross-pollination by insects does occur.
Chickpea leaf types
The pods are short, inflated and oval and typically contain one or two seeds. Plant height typically ranges from 25 to 65 cm, with kabuli types often slightly taller than desi types. The lowest seed pods are typically 10 to 15 cm from the soil surface under dry conditions.
- flower and stem colours
- flowering time
- green pod colour intensity
- leaflet type, colour, length and width
- maturity date
- plant height and attitude
- pod length and width
- presence of stem anthocyanin
- seed colour, shape and ribbing
Appendix IV: Field Bean Descriptions and Illustrations
Two basic plant types are found in dry edible bean, determinate (bush) or indeterminate (vining or trailing). Varieties may be classified according to plant types. For example, navy beans may be either of the bush or vining type.
There are three main growth habits of dry bean:
- Type I - determinate bush type;
- Type II - indeterminate bush type; and
- Type III - indeterminate vine type.
The determinate growth habit has five to nine nodes on the main stem with two to several branches. Stem elongation ceases when the terminal flower racemes of the main stem or lateral branches have developed. The indeterminate growth habit may have 12 to 15 nodes on the main stem. On indeterminate types, flowering and pod filling will continue simultaneously or alternately as long as temperature and moisture permit growth to occur.
Flowers will continue to develop over several weeks such that the youngest flowers at the top of the raceme may be just beginning to show flower colour while the older flowers at the base of the raceme are finished and pod set is beginning. The inspection should be conducted when the flower colour can be easily determined, approximately one week after the inception of flowering. In cooler temperatures flowering is delayed therefore the inspection could be conducted as late as two weeks after the inception of flowering, depending on local conditions.
- flower standard colour
- flower wing colour
- plant growth type
- pod beak length
- pod curvature
- pod length
- pod pigment
- seed colour
- terminal leaflet shape
- time to maturity
- vine length
Degree of pod curvature
Shape of pod curvature
Appendix V: Lupin Descriptions and Illustrations
Lupins are among the oldest cultivated crops in the world. The three most important agricultural species are the white lupin (Lupinus albus), yellow lupin (L. luteus) and blue lupin (L. angustifolius). The white lupin exists in both low (sweet) and high alkaloid (bitter) forms.
Sweet white lupin is an annual row crop that develops a vertical primary stem approximately 0.8 m tall with primary and secondary branches. Leaves are alternate, palmately divided into 10-15 narrowly oblong leaflets. The leaflets are smooth or hairy above, and very hairy beneath. Individual plants produce clusters of 3-7 pods, each containing 3-7 seeds. The seeds are cream-coloured and irregularly circular, and up to 6 cm in diameter. This species is primarily cross-pollinated but up to 50-85% self-pollination has been reported. Sweet white lupin is sensitive to low temperatures and photoperiod during germination; high temperatures during germination and long days may delay flowering. This species has an indeterminate growth habit so the plant may not mature uniformly. Lupins are grown for both grain and green manure.
- flower carina tip colour
- flower colour
- flowering time
- growth habit
- leaf colour at maturity
- plant height at maturity
- pod attitude
- pod length
- presence and intensity of stem anthocyanin
- seed colour and speckling at maturity
- terminal leaflet length and width
- time to maturity
Length of uppermost terminal leaflet
Keel tip colour of flower
Appendix VI: Lentil Descriptions and Illustrations
Lentil is classified into two types: Chilean or large-seeded (greater than 50 g per 1000 seeds) and Persian or small-seeded (40 g or less per 1000 seeds). Seed coat colour can vary from clear to light green to deep purple, mottled, grey, brown or black. Cotyledon (seed leaf) colour is yellow, red or green. The two main market classes are green and red.
Lentil plants are typically short compared to cereal crops, ranging from 20 to 75 cm in height. The first two nodes on the stem develop below or at the soil surface and are known as scale nodes. Injury to young lentil seedlings by late spring frost, heat canker or wind damage may cause the plant to initiate re-growth from a scale node below the soil surface. The third node on the stem is the usual site of the first leaf development. Lentil seedlings can produce a new node every four to five days under good growing conditions. Just prior to flowering, new leaves will develop a short tendril at the leaf tip.
Leaves are about 5 cm long with 9 to 15 leaflets. Lentil plants have an indeterminate growth habit allowing them to continue to flower until there is some form of stress such as moisture, nutrient deficiency, or high temperature. Flowers are self-pollinated.
Flower stalks produce one to three flowers which develop pods. Pods are less than 2.5 cm in length and contain one or two seeds. Most of the seed is produced by the aerial branches which form from the uppermost nodes on the main stem just below the first flowering node.
- flower colour
- hilum and cotyledon colours
- number stem nodes to first flower
- plant height
- ripe pod colour
- seed size and coat pattern
- time to flowering
- time to maturity
Appendix VII: Fababean Description
Fababean (Vicia faba) is an annual plant with coarse, upright and unbranched stems, 0.3 to 2 m tall, with 1 or more hollow stems coming from the base. The leaves are alternate, pinnate and consist of 2 to 6 leaflets, each up to 8 cm long. Unlike most other members of the genus, it is without tendrils or has only rudimentary tendrils.
Flowers are large, white with dark purple markings, borne on short pedicels in clusters of 1 to 5 on each axillary raceme usually between the 5th and 10th node; 1 to 4 pods develop from each flower cluster, and growth is indeterminate, though determinate mutants can occur. About 30% of the plants in a population are cross-fertilized and the main insect pollinators are bumblebees. There is a robust tap root with profusely branched secondary roots.
Based on seed size, two subspecies were recognized, Vicia paucijuga and Vicia faba. The latter was subdivided into V. faba var. minor with small rounded seeds (1 cm long), V. faba var. equina with medium sized seeds (1.5 cm) and V. faba var. major with large broad flat seeds (2.5 cm). (Bond et al., 1985; Smart, 1990).
- plant growth habit and type
- plant height
- presence and intensity of stem anthocyanin
- leaf colour
- basal leaflet length and width
- flowering time
- flower colour
- presence of melanin spots on flower wings
- presence and distribution of anthocyanin on flower standard
- pod length (excluding beak) and attitude
- pod colour and curvature
- seed size and coat colour
Appendix VIII: Diseases that May Affect Plant Appearance
Anthracnose of Lentils
Typical field symptoms are lodged plants with abnormally dark-brown stems. The lesions appear on the pods, stems, leaves, and seed. The lesions are grey to black in colour and appear sunken. A salmon-coloured ooze may appear in the centre of the lesion. The lesions may start out as small black spots. In mid-season, the leaves may start to fall off rapidly. The leaf veins will appear darkened. The stem will darken in colour and appear weakened.
Bean anthracnose, caused by Colletotrichum lindemuthianum, is almost worldwide in distribution. The disease is economically important as it affects seed quality, yield and marketability. There are numerous major races of the fungus that are characterized by the varieties they attack. Many varieties have been bred for resistance to one of more of the races.
Although infection may occur on both sides of the leaf and on the petiole, early signs of infection usually appear on the lower leaf surface along the veins, which show brick red to purplish red discolouration. Later, such discolouration also appears on the upper leaf surface. At the same time, brown lesions of various sizes with black, brown or purplish red margins develop around small veins. Dark brown eyespots that develop longitudinally along the stems are an early sign of stem infection. In the young seedling, the eyespots enlarge and the stem may break off. On older stems, the eye shaped lesion is limited to an approximate length of 5 to 7 mm and the lesion often has a sunken cankerous centre.
The most striking disease symptoms are small brown specks on rusty brown spots which appear on the pods. As the spots enlarge, their centres turn brown and many tiny black specks appear randomly on the brown area, replacing the brown specks. Each of the tiny black specks contains a mass of pinkish spores, often visible as a viscous droplet in humid conditions. The lesions on the pod usually reach a diameter of 5 to 8 mm. They are slightly sunken at the centre and have a dark brown or purplish brown margin. The seeds of heavily infected pods may show brown to light chocolate coloured spots on the seed coats. In badly infected seeds, the lesions may extend into the cotyledon.
Lentil, field pea, chickpea and faba bean all suffer from fungal diseases known as "ascochyta blight". Each crop kind is affected by a different species of ascochyta. As a result, lentil ascochyta will not spread to pea nor will pea ascochyta spread to lentil.
Ascochyta Blight of Chickpea
All above-ground portions of the plant are likely to show symptoms which begin as dark, sunken lesions. These soon erupt in pycnidia which often exhibit a pattern of concentric rings. Lesions may cause girdling of the stems or dieback of all plant parts above the lesions.
Ascochyta Blight of Faba Bean
Leaf spots are grey to brown, oval, and up to 1 cm in diameter with definite margins. Small, black pycnidia (small, black spore-producing structures) form in the center of lesions, often in a concentric ring pattern. Leaf spots may merge into irregular black patches causing a blighted appearance. Stem lesions are more elongated, usually sunken and reddish brown. Pod lesions are often sunken, tan to black, and frequently have darker margins. Infected seed may be discoloured and shrivelled.
Ascochyta Blight of Lentil
The first symptoms of ascochyta blight in lentils appear on the leaves. Symptoms appear on leaves, stems and pods as white to tan coloured spots, often with a darker margin. The centers of lesions are often speckled with pycnidia. When the disease becomes severe, leaves may drop prematurely and shoots may be blighted. Dieback and flower and pod abortion are the main causes of yield loss.
Ascochyta Blight of Pea
Leaf and stem symptoms include small, purplish-black, irregular flecks, which enlarge to 5 mm in diameter. Spots may also be brown with darker margins. Severe infection leads to drying of leaves, and stems may be blighted or girdled. On pods, lesions are initially small and dark, but purplish-brown discolouration may become extensive. Pycnidia may be produced on leaf or pod spots. Pod infection may lead to seed infection. Infected seed may occasionally be shrunken or discoloured but is more often symptomless. When infected seed is planted, seedlings with leaf spots or foot rot symptoms may be produced, or seedlings may die before emergence. Foot rot appears as purplish-black discolouration just above the soil line.
Seed discolouration develops later in the season after pods are infected. At this time, the seed surface becomes partially or completely brownish purple. Discolouration can continue to develop even after the crop is in the swath, particularly under damp weather conditions. Affected seed may also be shrivelled, and may have patches of white fungal growth and pycnidia on the surface.
Common Bacterial Blight
Common bacterial blight and fuscous blight are caused by Xanthomonas phaseoli and X. phaseoli var. fuscans. The symptoms of these diseases are virtually identical and the two diseases can only be distinguished in the laboratory. However, the two organisms may differ in the bean varieties that they infect. These two diseases are the most economically important bacterial bean diseases in Canada and they usually occur in late July and August and become progressively more severe as the field beans reach maturity.
The initial symptoms usually occur on the leaves. Infected leaves develop water-soaked or pale green spots that later turn brown and dry. These spots may merge to form irregular blotches of varying size. However, each spot or blotch has a narrow chlorotic margin around it. Similar spots may occur on the pods but in this case they may appear somewhat cankerous and greasy. The pod spots may merge to form blotches that have a reddish brown discolouration.
Foot Rot and Mycosphaerella Blight of Field Peas
Both fungi are stubble, seed, and soil borne and can survive for several years in the soil as resting spores. Initial infection occurs as the plant shoots come in contact with resting spores or by the fungus growing from seed across the point of attachment to the seedling. Infection from the seed develops as a foot lesion. Spores are produced from reproductive bodies of the fungus, and are released during wet weather to initiate leaf infection. During the growing season, new reproductive bodies are produced and release spores during wet periods to establish new infections.
Symptoms of foot rot usually begin at the point of seed attachment and extend as a bluish-black lesion to above the soil line.
Blight symptoms occur on leaves as small, purple lesions with indefinite margins that turn brownish-black and develop a target-like appearance. Lesions coalesce and leaves may dry up but remain attached to the stem. The lesions on the stem are purple and may extend 10 mm above and below the point of leaf attachment. Infection of the flowers causes the blossoms to drop. Small, purple lesions develop on infected pods. The pods may shrink if the infection is severe. Infected seeds may show various degrees of shrinkage and discolouration or they may show no signs of infection.
The seed crop inspector should look for bluish-black lesions on the stem, noting that stem lesions may merge and give the entire lower stem a bluish-black appearance. Infected pods are covered with small, purple lesions. The pods may appear shrunken if the infection is severe.
Powdery Mildew of Field Peas
Powdery mildew is a widespread disease that is often most prevalent on late-maturing field peas. In severe infestations, brown, pitted spots may occur on pods and the seed may be visibly affected. Premature ripening may result in shrunken seed.
Powdery mildew overwinters on plant debris. It appears as cottony-white to tan fungal colonies and yellowed blotches on the upper and lower surfaces of the leaves. It develops more severely on the lower leaves but it can infect any of the leaves in cool, humid weather. When the disease is severe, the pea plants are stunted, turn yellow, and defoliate.
A lush stand of peas is an ideal environment for powdery mildew development. Dew formation and lack of rainfall also favour the development of the disease. Optimum temperatures for development are between 20-25°C (68-75°F). Rain showers are actually disruptive to the spread of powdery mildew. The inoculum is spread by wind. Once it is established, powdery mildew increases very rapidly.
Symptoms consist of a light, greyish, powdery growth on the leaves, pods and occasionally on the stems. This powdery growth is easily rubbed off. As the plant ages, tiny fruiting bodies of the fungus often form in the powdery growth. They develop as spots that enlarge and merge to cover the entire surface of the leaves, pods and stems.
This disease affects dry beans, field peas, and lentils. The symptoms usually develop several weeks after flowering begins. The plants develop pale-grey to white lesions, at or above the soil line and on upper branches and pods. The infections often develop in the axils where the leaf and the stem join because the infected petals lodge there. Infected stems appear bleached and tend to shred. Hard black fungal bodies (sclerotia), of varying sizes, develop within the infected stems, branches, or pods. Plants with girdled stems wilt and ripen prematurely. Sclerotia overwinter in the soil and produce disease spores the next year infecting the next crop.
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