Fire blight of apple and pear

Fire blight of apple and pear

Johnson, Okay.B. 2000. Fireplace blight of apple and pear.
The Plant Well being Teacher. DOI: 10.1094/PHI-I-2000-0726-01
Up to date 2015.

 Fireplace blight of apple and pear

 Erwinia amylovora

 Apple, pear, a number of rosaceous ornamentals

Kenneth B. Johnson,
Oregon State College

Erwinia amylovora is a local pathogen of untamed, rosaceous hosts in japanese North America. It was the primary bacterium confirmed to be a pathogen of vegetation. As we speak, fireplace blight is a crucial illness of apples and pears in lots of elements of the world.

Pear shoot with fire blight. (Courtesy K. Johnson)

Pear shoot with fireplace blight. (Courtesy Okay. Johnson)

Signs and Indicators

Signs of fireplace blight could be noticed on all above floor tissues together with blossoms, fruits, shoots, branches and limbs, and within the rootstock close to the graft union on the decrease trunk. Usually, signs of fireplace blight are simple to acknowledge and distinguishable from different ailments.

Blossom clusters and younger shoots

Blossom signs are first noticed 1-2 weeks after petal fall. The floral receptacle, ovary, and peduncles change into water soaked and boring, grayish inexperienced in look. Later these tissues shrivel and switch brown to black. Related signs typically develop within the base of the blossom cluster and younger fruitlets because the an infection spreads internally (Determine 2). During times of excessive humidity, small droplets of bacterial ooze type on water-soaked and discolored tissues (see instance on fruit, Determine 7). Ooze droplets are initially creamy white, changing into amber-tinted as they age.

Figure 2. Pear blossom cluster with fire blight (Courtesy D. Sugar)

Determine 2

Figure 7. Apple fruit with fire blight showing signs of bacterial ooze (Courtesy NYSAES)

Determine 7

Shoot signs

Shoot signs are just like these in blossoms however develop sooner. Suggestions of shoots could wilt quickly to type a “shepherd’s criminal” (Figures 1 and three). Leaves on diseased shoots typically present blackening alongside the midrib and veins earlier than changing into totally necrotic. Quite a few diseased shoots give a tree a burnt, blighted look, therefore the illness identify (Determine 4).

Figure 1. Pear shoot with fire blight. (Courtesy K. Johnson)

Determine 1

Figure 3. Apple shoot with fire blight showing shepard’s crook symptom. (Courtesy A. Jones)

Determine 3

Figure 4. Burnt appearance of apple caused by severe fire blight. (Courtesy T. Smith)

Determine 4

Superior foliar signs

Infections initiated in blossoms and shoots can proceed to increase each up and down bigger branches and limbs. Bark on youthful branches turns into darkened and water-soaked (Determine 5). At superior levels, cracks will develop within the bark, and the floor can be sunken barely (Determine 6). Amber-colored bacterial ooze blended with plant sap could also be current on bark. Wooden beneath the bark will present streaked, brown to black discolorations.

Figure 5. Vegetative shoots of pear: healthy (right) and diseased with fire blight (left). (Courtesy D. Sugar)

Determine 5

Figure 6. Active (left) and dormant (right) fire blight cankers on mature apple branches. (Courtesy A. Jones)

Determine 6

Pear and apple fruits

Indeterminate, water-soaked lesions type on surfaces of immature fruit and later flip brown to black. Droplets of bacterial ooze could type on lesions, often in affiliation with lenticels (Determine 7). Severely diseased fruits blacken utterly and shrivel.

Apple rootstocks

Rootstock infections often develop close to the graft union because of inner motion of the pathogen by way of the tree or from infections by way of water sprouts or burr knots. The bark of contaminated rootstocks could present water-soaking, a purplish to black discoloration, cracking, and indicators of bacterial ooze. Purple-brown to black streaking could also be obvious in wooden just below the bark (Determine 8). Signs of rootstock blight could be confused with Phytophthora collar rot. M.26 and M.9 rootstocks are extremely inclined to the pathogen.

Figure 8. Symptoms of fire blight on apple rootstock. (Courtesy M. Ellis)

Determine 8

Pathogen Biology

Erwinia amylovora is a member of the household Enterobacteriacae. Cells of
E. amylovora are gram-negative, rod-shaped, measure 0.5-1.Zero x 3.Zero mm, and flagellated on all sides (peritrichous) (Determine 9). Physiologically,
E. amylovora is classed as a facultative anaerobe. It grows on most traditional microbiological media and on a number of differential media. Optimum temperature for progress is 27°C (81°F), with cell division occurring at temperatures starting from 5 to 31°C (41 to 88°F). Identification of
E. amylovora isolates is predicated on biochemical assessments, inoculation of immature pear fruits and apple seedlings, sequencing of the 16S ribosomal RNA gene and thru use of species-specific PCR primers.

Figure 9. Electron micrograph of an Erwinia cell showing peritrichous flagella. (Courtesy Oregon State University)

Determine 9

Figure 10. Apples blossoms with honey bee. (Courtesy K. Johnson)

Determine 10

Epiphytic and endophytic biology

On flowers,
E. amylovora is a wonderful colonizer of the surfaces of stigmas and, to a lesser extent, the floor of the nectary. This copy on floral surfaces known as epiphytic progress and happens with out the bacterium inflicting illness. Epiphytic progress of
E. amylovora on stigmas mixed with motion of the pathogen from flower to flower by pollinating bugs (Determine 10) are two essential processes that regulate the incidence of blossom an infection.
Erwinia amylovora can also survive on different wholesome plant surfaces, akin to leaves and branches, for restricted intervals (weeks), however colony institution and epiphytic progress on these surfaces doesn’t happen. Cells of
E. amylovora excrete giant quantities of an extracelluar polysaccharide (a serious element of bacterial ooze), which creates a matrix that protects the pathogen on plant surfaces. In propagation nurseries, cells of
E. amylovora surviving on woody surfaces can provoke illness when scions and rootstocks are wounded throughout grafting.
Erwinia amylovora can also reside as an endophyte inside apparently wholesome plant tissue, akin to branches, limbs, and budwood. Migration of the pathogen by way of xylem is one mechanism by which floral infections of apple can result in rootstock infections close to the graft union.

Illness Cycle and Epidemiology


disease cycle 

Illness Cycle


Erwinia amylovora overwinters in a small proportion of the annual cankers that have been shaped on branches diseased within the earlier season. These overwintering websites are referred to as “holdover cankers”. As temperatures heat in spring, the pathogen turns into lively within the margins of holdover cankers. Free bacterial cells are launched onto the bark floor, typically as seen ooze. Bugs interested in the ooze (e.g., flies) or rain disseminate the micro organism from the canker to flowers.

Floral epiphytic part

Stigmas, that are borne on the tip of the kinds, are the principal website of epiphytic colonization and progress by
E. amylovora. Throughout the floral epiphytic part, the final word inhabitants measurement that the pathogen attains is influenced by temperature, which regulates the era time of the pathogen, and by the variety of blossoms through which the pathogen turns into established, which is facilitated by pollinating bugs, honey bees specifically. Below superb situations, stigmas of every flower can help ~106 cells of the pathogen.

Major an infection in flowers

Blossom blight is initiated when cells of
E. amylovora are washed externally from the stigma to the hypanthium (floral cup). On the hypanthium,
E. amylovora features entry to the plant by way of secretory cells (nectarthodes) situated on the floor. In pear, the significance of blossom blight is expanded additional by the tendency of this species to provide nuisance, secondary or “rattail” flowers throughout late spring and early summer season, lengthy after the interval of major bloom.

Secondary phases

This contains shoot, fruit, and rootstock blight. These phases are often initiated by inoculum produced on tissues diseased because of blossom an infection. Wounds are usually required by
E. amylovora to provoke shoot and fruit blight. Bugs, akin to plant bugs and psylla, create wounds on succulent shoots throughout feeding. Sturdy winds, rain, and hail can create quite a few, giant wounds in host tissues. An infection occasions induced by extreme climate are typically referred to as “trauma blight.” Rootstock blight of apple may end up from shoot blight on water sprouts or from inner translocation of
E. amylovora from infections increased on the tree.

Canker growth

Each major and secondary infections can increase all through the summer season, with the final word severity of an an infection being depending on the host species, cultivar, surroundings, and age and dietary standing of the host tissues. Younger, vigorous tissues and timber are extra inclined to fireside blight than older, slower rising tissues or timber. Equally, timber which have acquired an extra of nitrogen fertilizer, and due to this fact are rising quickly, are extra inclined than timber rising beneath a balanced nutrient regime. Charges of canker growth additionally could be enhanced by a excessive water standing in a tree attributable to extreme or frequent irrigation or poorly drained soils. Canker growth slows in late summer season as temperatures cool and progress charges of timber and shoots decline.

Epidemiological fashions

Blossom blight is sporadic from season to season owing to the requirement for heat temperatures to drive the event of enormous epiphytic populations. A number of epidemiological fashions (e.g., COUGARBLIGHT, MARYBLYT) predict the probability of blossom blight epidemics primarily based on noticed weather conditions (Determine 11). The fashions work by figuring out the intervals conducive for epiphytic progress of
E. amylovora on blossoms earlier than an infection happens, and thus are used broadly to assist choices on the necessity for and timing of chemical purposes. Blossom blight threat fashions accumulate diploma models above a threshold temperature of 15.5 (60°F) or 18°C (64°F). Information on rain or blossom wetness in periods of heat climate are additionally used within the fashions to point extra exactly the timing and probability of floral an infection. Different temperature-based fashions predict the time to symptom expression after an an infection occasion (i.e., the size of the incubation interval) primarily based on warmth unit sums. These fashions are used to time orchard inspections and/or pruning actions.

Figure 11. Automated weather station used to provide data for epidemiological models. (Courtesy J. Pinkerton)

Determine 11

Illness Administration

Efficient administration of fireplace blight is multi-faceted and largely preventative. The grower should make the most of a mix of sanitation, cultural practices, and sprays of chemical or organic brokers to maintain the illness in test.


Choice of a resistant cultivar is the simplest technique of controlling fireplace blight. In apple, for instance, some cultivars exist which can be reasonably proof against the illness (e.g., Purple and Golden Scrumptious). For pears, cultivar decisions are extra restricted as a result of superior horticultural traits (e.g., style, storage, and advertising and marketing qualities) have been troublesome to mix with increased ranges of illness resistance. In recent times, fireplace blight has change into extra widespread in apples as a result of the spectrum of cultivars grown commercially has expanded and shifted towards these with better susceptibility to the illness (e.g., Fuji, Gala, Pink Girl). With this shift has come the popularity that well-liked dwarfing rootstocks for apple, M.9 and M.26, are extremely inclined to
E. amylovora. Dwarfing rootstocks with resistance to fireside blight are being developed and commercialized (e.g., the Geneva rootstock collection from Cornell College). Many decorative cultivars additionally present excessive ranges of fireplace blight resistance.

Elimination of overwintering inoculum

Vigilant sanitation by way of the removing of increasing and overwintering cankers is important for management of fireplace blight in inclined cultivars. Elimination of overwintering (“holdover”) cankers is completed by inspecting and pruning timber in the course of the winter.

Prevention of blossom blight

Prevention of blossom an infection is essential in fireplace blight administration as a result of infections initiated in flowers are damaging and since the pathogen cells originating from floral infections present a lot of the inoculum for secondary phases of the illness, together with the an infection of shoots, fruits, and rootstocks. Administration actions to suppress blossom blight goal the floral epiphytic part. Sprays of antibiotics, streptomycin, oxytetracycline or kasugamycin, have successfully suppressed blossom an infection in business orchards (Determine 12).

Figure 12. Application of antibiotics to apples for prevention of blossom blight. (Courtesy T. Smith)

Determine 12

Copper compounds are also efficient however purposes are generally restricted to the pre-bloom interval as a result of copper ions in answer could be phytotoxic to the pores and skin of younger fruits.
E. amylovora has change into proof against streptomycin in some manufacturing areas, limiting the effectiveness of this chemical. Non-pathogenic, microbial epiphytes sprayed onto flowers can preemptively suppress fireplace blight by colonizing the area of interest (stigmatic floor) utilized by
E. amylovora to extend its epiphytic inhabitants measurement. The bacterium
Pseudomonas fluorescens pressure A506, is registered and bought commercially for this function (BlightBan A506) as is the yeast,
Aureobasidium pullulans (Blossom Defend).

Mid-season suppression of established infections

In summer season, established infections are managed principally by pruning. Efficient management by way of pruning requires that cuts are made 20-30 cm (Eight to 12 inches) beneath the seen finish of the increasing canker (Determine 13) and that between cuts the pruning instruments are disinfested with a bleach or alcohol answer to stop cut-to-cut transmission. Repeated journeys by way of an orchard are crucial, as some as infections are invariably missed and others change into seen at later occasions (Determine 14). Prunings harboring the pathogen are often destroyed by burning (Determine 15).

Figure 13. Pruning of fire blight 20-25 cm below active infection. (Courtesy T. Smith)

Determine 13

Figure 14. Pruning of pear orchard to remove active fire blight cankers. (Courtesy T. Smith)

Determine 14

Figure 15. Severe fire blight of pear in foreground with burning of diseased prunings in background. (Courtesy D. Sugar)

Determine 15

In severely affected orchards, cultural practices that sluggish the expansion fee of the tree will even sluggish the speed of canker improvement. This contains withholding irrigation water, nitrogen fertilizer, and cultivation. Equally, practices that cut back tree wounding and bacterial motion can cut back secondary an infection. This contains controlling bugs akin to plant bugs and psylla, limiting use of limb spreaders in younger orchards, and avoiding the use overhead sprinklers. Chemical compounds akin to streptomycin or copper can suppress trauma blight if utilized instantly after a hailstorm.


Erwinia amylovora is a local pathogen of untamed, rosaceous hosts in japanese North America. These hosts embody hawthorn, serviceberry, and mountain ash. Early European settlers launched apple and pear to North America. The primary report of fireplace blight as a illness of apple and pear occurred in 1780, within the Hudson Valley of New York. In California, the illness was first reported in 1887.

Early 19th and 20th century horticultural texts and bulletins acknowledged fireplace blight as a critical illness of pear, supplied descriptions of signs, and outlined pruning practices for management (Determine 16). Nonetheless, within the japanese United States, fireplace blight proved to be destructively epidemic on pear, limiting the cultivation of this host. Even at this time, the specter of fireplace blight restricts business manufacturing of pear to semi-arid, desert areas west of the Rocky Mountains.

Figure 16. 1915 fire blight control bulletin. (Courtesy I. Cardiff, Washington State University)

Determine 16

​Erwinia amylovora has the excellence of being the primary bacterium proven to be a pathogen of vegetation. Koch’s postulates for
E. amylovora have been fulfilled by J.C. Arthur in 1885, however the genesis of the idea that micro organism could be plant pathogens required the contributions of many scientists (notably T.J. Burrill) and growers over a interval extending from 1846 to 1901.
E. amylovora can also be one of many first plant pathogens to be related to an insect vector. Within the late 1890’s, M.B. Waite linked blossom an infection to the motion of the pathogen from flower-to-flower by pollinating bugs.

Throughout the 20th century, introductions of infested plant materials served to determine
E. amylovora in Europe, the Center East, and New Zealand. In 1995, fireplace blight was first noticed within the Po River Valley of northern Italy, which is the most important pear manufacturing space on this planet. Since 1995, the Italian authorities has destroyed 500,000 pear timber in an try to eradicate
E. amylovora. Just lately, fireplace blight has unfold eastward from the Center East to the northern Himalayan foothills of central Asia (Kazakhstan, Kyrgyzstan), which is the middle of origin for
Malus (apple) spp.

Chosen Studying and References

Baker, Okay. F. 1971. Fireplace Blight of pome fruits: The genesis of the idea that micro organism could be pathogenic to vegetation. Hilgardia 40:603-633.

Beer, S.V. 1990. Fireplace Blight. Pages 61-63 in:
Compendium of Apple and Pear D​is​eases and Pests. Jones, A.L., and Aldwinckle, H.S. (eds.). APS Press, St. Paul, MN.

Johnson, Okay.B., and V.O. Stockwell. 1998. Administration of fireplace blight: A case research in microbial ecology. Annu. Rev. Phytopathol. 36: 227-248.

McManus, P. and V. Stockwell. 2000. Antibiotics for plant illness management:
Silver bullets or rusty sabers?

Smith, T. J. 2015.
The event and use of Cougar Blight 1990 – 2010: A situation-specific fireplace blight threat evaluation mannequin for apple and pear. 

Turechek, W. W., and Biggs, A. R. 2015. Maryblyt v. 7.1 for Home windows: An improved fireplace blight forecasting program for apples and pears. Plant Well being Progress doi:10.1094/PHP-RS-14-0046.

van der Zwet, T., and S.V. Beer. 1995. Fireplace Blight – Its Nature, Prevention, and Management: A Sensible Information to Built-in Illness Administration. U.S. Dept. Agric., Agricultural Data Bull. No. 631.

van der Zwet, T., Orolaza-Halbrendt, N., and Zeller, W. 2012. Fireplace Blight: Historical past, Biology, and Administration, APS Press, St. Paul, MN. 460 pp.Vanneste, J.L. (ed.) 2000. Fireplace Blight: The illness and its causative agent,
Erwinia amylovora. CABI Publishing, Wallingford, UK.

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