Disease resistance in fruit and vegetables
Encyclopedia
There are a number of lines of defence against pest
s (that is, those animals that cause damage to the plants we grow) and diseases in the organic garden, principal among these being the practice of good husbandry, creating healthy soil
and ensuring high standards of garden hygiene. But no matter how diverse and healthy the garden eco-system may be, there will always be a degree of disease and pest presence. In many ways, some level of pathogen
population in the garden can be not only acceptable but desirable as they are indicative of a generally healthful and diverse environment, and add to the overall robustness of the system as an immunity to such detrimental influences will build up, particularly in a balanced polycultural
regime. Indeed, most of the plants we grow will tend to be selected because they are trouble free, and those that are more susceptible to attack will have fallen by the wayside over time. However, most farmers find it unacceptable that the food crops they grow are damaged by pests.
For these crops there has been considerable research and selective breeding carried out in order to find cultivar
s that are resistant or immune to pest and disease damage. Breeding for plant disease resistance
generally has involved finding suitable genetic
material amongst existing stocks or in the wild, which is then incorporated into commercial varieties.
(Venturia inaequalis
), powdery mildew
(Podosphaera leucotricha), orchard fireblight
(Erwinia amylovora), woolly apple aphid (Eriosoma lanigerum) and collar rot (Phytophthora cactorum), the main sources of resistant material used in breeding programmes such as those being run by East Malling Research Station
in England or Hortresearch
in New Zealand are major gene resistances derived from crab-apples. The Vf gene for black spot resistance is derived from the ornamental crab-apple species Malus floribunda. Most black spot resistant cultivars developed around the world carry this gene, but there are some selections that carry the Vr (from M. pumila) or Vm (from M. micromalus) gene. Major gene resistances to powdery mildew are derived from M. robusta (Pl1) and M. zumi (Pl2), and the apple cultivar Northern Spy has a long-standing reputation for its major gene resistance to woolly apple aphid. Since early this century this resistance has been used to develop woolly aphid resistant rootstocks such as MM.106 and M.793. Much later it was shown that the cultivar was also very resistant to collar rot and a useful breeding parent for this resistance.
The most valuable form of resistance is where the pest cannot survive as well on one variety as on another. In some cases this can actually make the plants immune to attack, as is the case with the lettuce
s Avoncrisp and Avondefiance which were bred at the Institute of Horticultural Research
, Wellesbourne
during the 1960s, which are fully resistant to lettuce root aphid (Pemphigus bursarius).
resistant to the Fusarium
fungus (Fusarium oxysporum spp.) may not succumb to this disease, but may also be unacceptably short, ribby and low yielding.
Further, a cultivar that is resistant to one disease may be more susceptible to another that is equally important. A lettuce cultivar that is resistant to mosaic virus may be sensitive to corky root disease, whilst another that resists corky root may be vulnerable to downy mildew
(Brim lactic).
Another drawback to resistance is that depending on the host pathogen system, resistance is sometimes not long lasting as new pathogen strains quickly develop, and further research and breeding is constantly needed.
family, no acceptable resistant cultivars are yet available. In addition, commercial seed companies and plant breeders rarely invest resources into developing resistant cultivars for more minor or speciality crops, which often tend to be those of greater interest to the organic grower.
In general it is probably fair to say that resistance will not fully guarantee total crop protection
, but choosing resistant varieties should rather be considered as a part of an overall Integrated pest management
strategy, especially against virus
diseases. In particular they can be especially useful where the threat from specific pests and diseases is high.
Pest (animal)
A pest is an animal which is detrimental to humans or human concerns. It is a loosely defined term, often overlapping with the related terms vermin, weeds, parasites and pathogens...
s (that is, those animals that cause damage to the plants we grow) and diseases in the organic garden, principal among these being the practice of good husbandry, creating healthy soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
and ensuring high standards of garden hygiene. But no matter how diverse and healthy the garden eco-system may be, there will always be a degree of disease and pest presence. In many ways, some level of pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
population in the garden can be not only acceptable but desirable as they are indicative of a generally healthful and diverse environment, and add to the overall robustness of the system as an immunity to such detrimental influences will build up, particularly in a balanced polycultural
Polyculture
Polyculture is agriculture using multiple crops in the same space, in imitation of the diversity of natural ecosystems, and avoiding large stands of single crops, or monoculture...
regime. Indeed, most of the plants we grow will tend to be selected because they are trouble free, and those that are more susceptible to attack will have fallen by the wayside over time. However, most farmers find it unacceptable that the food crops they grow are damaged by pests.
For these crops there has been considerable research and selective breeding carried out in order to find cultivar
Cultivar
A cultivar'Cultivar has two meanings as explained under Formal definition. When used in reference to a taxon, the word does not apply to an individual plant but to all those plants sharing the unique characteristics that define the cultivar. is a plant or group of plants selected for desirable...
s that are resistant or immune to pest and disease damage. Breeding for plant disease resistance
Plant disease resistance
Plant disease resistance is crucial to the reliable production of food, and it provides significant reductions in agricultural use of fuel, land, water and other inputs. There are numerous examples of devastating plant disease impacts , as well as recurrent severe plant disease issues...
generally has involved finding suitable genetic
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
material amongst existing stocks or in the wild, which is then incorporated into commercial varieties.
Example: The apple
In the case of apples, in which research is being carried out in order to develop resistance to diseases such as apple scabApple scab
Apple scab is a disease to Malus trees, such as apple trees, caused by the ascomycete fungus Venturia inaequalis. The disease manifests as dull black or grey-brown lesions on the surface of tree leaves, buds or fruits. Lesions may also appear less frequently on the woody tissues of the tree. Fruits...
(Venturia inaequalis
Venturia inaequalis
Venturia inaequalis is an ascomycete fungus that causes the Apple scab disease.-Systematics:Venturia inaequalis anamorphs have been described under the names Fusicladium dendriticum and Spilocaea pomi. Whether V. inaequalis is a single species or contains several cryptic species has been a matter...
), powdery mildew
Powdery mildew
Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of fungi in the order Erysiphales. It is one of the easier diseases to spot, as its symptoms are quite distinctive. Infected plants display white powdery spots on the...
(Podosphaera leucotricha), orchard fireblight
Fireblight
Fire blight, also written fireblight, is a contagious disease affecting apples, pears, and some other members of the family Rosaceae. It is a serious concern to producers of apples and pears...
(Erwinia amylovora), woolly apple aphid (Eriosoma lanigerum) and collar rot (Phytophthora cactorum), the main sources of resistant material used in breeding programmes such as those being run by East Malling Research Station
East Malling Research Station
East Malling Research is a now private company located in East Malling, Kent in England.-History:A research station was established on the East Malling site in 1913 on the impetus of local fruit growers. The original buildings are still in use today...
in England or Hortresearch
HortResearch
HortResearch was a Crown Research Institute of New Zealand. The focus of research in this company was mainly in the development of new fruit varieties and other food products...
in New Zealand are major gene resistances derived from crab-apples. The Vf gene for black spot resistance is derived from the ornamental crab-apple species Malus floribunda. Most black spot resistant cultivars developed around the world carry this gene, but there are some selections that carry the Vr (from M. pumila) or Vm (from M. micromalus) gene. Major gene resistances to powdery mildew are derived from M. robusta (Pl1) and M. zumi (Pl2), and the apple cultivar Northern Spy has a long-standing reputation for its major gene resistance to woolly apple aphid. Since early this century this resistance has been used to develop woolly aphid resistant rootstocks such as MM.106 and M.793. Much later it was shown that the cultivar was also very resistant to collar rot and a useful breeding parent for this resistance.
Resistance and immunity
Some plants can tolerate the presence of large numbers of insects without being severely affected. This is not very satisfactory however as insects will still cause damage, and in fact further breeding and population expansion of the pest species is supported. Other varieties are less attractive to pests, but this can be difficult to sustain or demonstrate.The most valuable form of resistance is where the pest cannot survive as well on one variety as on another. In some cases this can actually make the plants immune to attack, as is the case with the lettuce
Lettuce
Lettuce is a temperate annual or biennial plant of the daisy family Asteraceae. It is most often grown as a leaf vegetable. It is eaten either raw, notably in salads, sandwiches, hamburgers, tacos, and many other dishes, or cooked, as in Chinese cuisine in which the stem becomes just as important...
s Avoncrisp and Avondefiance which were bred at the Institute of Horticultural Research
Horticulture Research International
Warwick HRI, formerly part of Horticulture Research International, is an United Kingdom organisation tasked with carrying out horticultural research and development and transferring the results to industry in England....
, Wellesbourne
Wellesbourne
Wellesbourne is a large village and civil parish in the county of Warwickshire, in the West Midlands region of the UK. In the 2001 census the parish, which also includes the village of Walton, had a population of 5,691 Wellesbourne is a large village and civil parish in the county of Warwickshire,...
during the 1960s, which are fully resistant to lettuce root aphid (Pemphigus bursarius).
Trade-off of breeding for resistance
Sometimes however there can be a trade-off, for those varieties which have increased immunity or resistance may be lacking in other qualities such as flavour, yield or quality. CeleryCelery
Apium graveolens is a plant species in the family Apiaceae commonly known as celery or celeriac , depending on whether the petioles or roots are eaten: celery refers to the former and celeriac to the latter. Apium graveolens grows to 1 m tall...
resistant to the Fusarium
Fusarium
Fusarium is a large genus of filamentous fungi widely distributed in soil and in association with plants. Most species are harmless saprobes, and are relatively abundant members of the soil microbial community. Some species produce mycotoxins in cereal crops that can affect human and animal health...
fungus (Fusarium oxysporum spp.) may not succumb to this disease, but may also be unacceptably short, ribby and low yielding.
Further, a cultivar that is resistant to one disease may be more susceptible to another that is equally important. A lettuce cultivar that is resistant to mosaic virus may be sensitive to corky root disease, whilst another that resists corky root may be vulnerable to downy mildew
Downy mildew
Downy mildew refers to any of several types of oomycete microbes that are obligate parasites of plants. Downy mildews exclusively belong to Peronosporaceae. In commercial agriculture, they are a particular problem for growers of crucifers, grapes and vegetables that grow on vines...
(Brim lactic).
Another drawback to resistance is that depending on the host pathogen system, resistance is sometimes not long lasting as new pathogen strains quickly develop, and further research and breeding is constantly needed.
Availability of resistant varieties
Resistant varieties are not available for all crops. For several of the most damaging plant diseases, such as Potato blight (Phytophthora infestans) and white rot (Sclerotic cepivorum) of the AlliumAllium
Allium is a monocot genus of flowering plants, informally referred to as the onion genus. The generic name Allium is the Latin word for garlic....
family, no acceptable resistant cultivars are yet available. In addition, commercial seed companies and plant breeders rarely invest resources into developing resistant cultivars for more minor or speciality crops, which often tend to be those of greater interest to the organic grower.
In general it is probably fair to say that resistance will not fully guarantee total crop protection
Crop protection
Crop protection is the branch of horticulture concerned with protecting crops from pests, weeds, disease and theft.It encompasses:* Pesticide-based approaches such as herbicides, insecticides and fungicides...
, but choosing resistant varieties should rather be considered as a part of an overall Integrated pest management
Integrated Pest Management
Integrated pest management is an ecological approach to agricultural pest control that integrates pesticides/herbicides into a management system incorporating a range of practices for economic control of a pest...
strategy, especially against virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
diseases. In particular they can be especially useful where the threat from specific pests and diseases is high.
Table of resistant crops
The table below illustrates a number of pest and disease resistant vegetable crop varieties, although should not be considered comprehensive.| Crop | Variety | Comments |
| French Bean | Aigullion | Resistant to bean mosaic virus and anthracnose |
| Hildora | Tolerant of bean mosaic virus | |
| Maxi | Tolerant of bean mosaic virus | |
| Nektar Queen | Resistant to bean mosaic virus | |
| Farba | Resistant to bean mosaic virus | |
| Hilda | Resistant to bean mosaic virus | |
| Broad Bean | Futura | Tolerant of chocolate spot |
| Brussels sprouts | Cavalier | Resistant to light leaf spot |
| Braveheart F1 | Resistant to powdery mildew and light leaf spot | |
| Cabbage | Stonehead F1 | Resistant to mildew |
| Calabrese | Emperor F1 | Highly tolerant of black rot and downy mildew |
| Sampson F1 | Highly resistant to black rot and downy mildew | |
| Carrot | Fly Away F1 | Bred for resistance to carrot fly |
| Newmarket | Good resistance to splitting | |
| Cucumber | Bush Champion F1 | Resistant to cucumber mosaic virus |
| Marketmore | Resistant to cucumber mosaic virus | |
| Burpless Tasty Green F1 | Resistant to mildew and tolerant of heat | |
| Slice King F1 | Resistant to downy and powdery mildew, gummosis and angular leaf spot | |
| Cumlaude F1 | Tolerant of powdery mildew | |
| Media F1 | Tolerant of powdery mildew | |
| Leek | Swiss Giant, Zermatt | Moderate rust resistance |
| Alvitta | Rust Tolerant | |
| Conora | Good resistance to rust | |
| Lettuce | Alexandria | Highly resistant to downy mildew and bolting |
| Lisbusa | Resistant to downy mildew, tolerant of mosaic virus, root aphid and tipburn | |
| Sylvestra | Resistant to downy mildew and aphids | |
| Little Gem | Resistant to root aphid | |
| Barcelona | Resistant to aphids and mildew | |
| Iglo | Resistant to downey mildew | |
| Revolution | Resistant to mildew and bolting | |
| Smile | Resistant to aphids, mildew, tipburn and bolting | |
| Parsnip | Avonreister | Very good resistance to canker Canker Canker and anthracnose are general terms for a large number of different plant diseases, characterised by broadly similar symptoms including the appearance of small areas of dead tissue, which grow slowly, often over a period of years. Some are of only minor consequence, but others are ultimately... |
| Gladiator F1 | High resistance to canker Canker Canker and anthracnose are general terms for a large number of different plant diseases, characterised by broadly similar symptoms including the appearance of small areas of dead tissue, which grow slowly, often over a period of years. Some are of only minor consequence, but others are ultimately... |
|
| Tender and True | Good canker Canker Canker and anthracnose are general terms for a large number of different plant diseases, characterised by broadly similar symptoms including the appearance of small areas of dead tissue, which grow slowly, often over a period of years. Some are of only minor consequence, but others are ultimately... resistance |
|
| Pea | Ambassador | Resistant to powdery mildew, entation virus and fusarium wilt |
| Cavalier | Good resistance to powdery mildew. | |
| Greenshaft | Resistant to downy mildew and fusarium wilt | |
| Rondo | Resistant to fusarium wilt | |
| Potato (first early) | Colleen | Good resistance to blight and scab |
| Premiere | Resistant to blight and spraing | |
| Pentland Javelin | Good all round disease resistance, including golden eelworm and scab | |
| Swift | Resistant to golden eelworm and tolerant to blackleg | |
| Potato (second early) | Cosmos | Resistant to blight and common scab |
| Osprey | Very resistant to scab and eelworm | |
| Potato (maincrop) | Harmony | Very resistant to scab and partially resistant to white and golden eelworm |
| Milva | Blight resistant | |
| Remarka | Good all around disease resistance | |
| Admiral | Good resistance to blight and scab | |
| Cara | Blight resistant | |
| Valor | Good overall disease resistance combined with high eelworm and blight resistance | |
| Pepper | Bell Boy F1 | Mosaic virus resistant |
| Mandy F1 | Highly resistant to mosaic virus | |
| Sweetcorn | Golden sweet F1 | Highly resistant to smut |
| Tomato | Alicante | Good resistance to greenback and mildew |
| Libra F1 | Resistant to fusarium crown and root rot | |
| Shirley F1 | Resistant to fusarium, cladosporium and TMV |
See also
- Plant disease resistancePlant disease resistancePlant disease resistance is crucial to the reliable production of food, and it provides significant reductions in agricultural use of fuel, land, water and other inputs. There are numerous examples of devastating plant disease impacts , as well as recurrent severe plant disease issues...
- Plant Pathology
- plant defense against herbivoryPlant defense against herbivoryPlant defense against herbivory or host-plant resistance describes a range of adaptations evolved by plants which improve their survival and reproduction by reducing the impact of herbivores. Plants use several strategies to defend against damage caused by herbivores...