Apple scab lecture final 2018
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Apple scab is the most economically important disease of apples worldwide. In India, it causes up to 70% crop loss in some years. The fungus Venturia inaequalis overwinters in fallen leaves and produces spores that are spread by wind and rain to infect young apple leaves and fruits. Symptoms include olive green spots that later turn black on leaves and corky brown spots on fruit. Resistance breeding and forecasting models are used to manage the disease, but conventional breeding is slow. Introducing resistance genes from wild crabapples through biotechnology may enable faster development of resistant varieties.
Apple scab lecture final 2018
- 1. Apple scab M.K. Verma, Ph.D., ARS (1995), FHSI, FISNS Principal Scientist (Hort) Division of Fruits and Horticultural Technology ICAR-Indian Agricultural Research Institute New Delhi, India E-mail: mahenicar10@gmail.com
- 3. Important diseases of apple
- 4. Disease Incidence (%) Reference (s) Present status/ assessment Scab 70% Gupta (1978) Severe/traces Marssonina Blotch 65-80 Sharma (2000) Severe Leaf spots (Alternaria sp) 40 Sharma et al., (2005) Moderate Powdery Mildew --- -- Severe in nursery and moderate in orchards White root rot 30-35 Sharma et al., (2003) Severe Collar rot ---- - Moderate Seedling blight 40 Bhardwaj and Agarwala (1986) Severe in warmer areas Sooty blotch and flyspeck 40-50 Severe Storage Rots 10-15 Agarwala and Sharma (1968) Moderate Storage Rots 10.3-18 Kaul and Munjal (1982) Moderate Blue mould rot 5.8-8.0 Kaul and Munjal (1982) Moderate Bitter rot 2.12 Kaul and Munjal (1982) Moderate Pink rot 1.81 Kaul and Munjal (1982) Moderate Whisker’s rot 0.75 Kaul and Munjal (1982) Moderate Brown rot 1.5 Kaul and Munjal (1982) Moderate Core Rot 10-40 Raina et. al. (1971) Moderate Brown rot 5-15.2 Sharma & Kaul (1989) Moderate Cankers 1-25 Shandilya et al., 1973 Severe Incidence and present status of various diseases of apple in India
- 5. Plant Species Disease Incidence (%) Reference (s) Present status/ assessment Pear Storage rots 11.8 Sharma (1989) Moderate Grey mould 33.0 Sharma (1989) Moderate Brown rot 24.6 Sharma (1989) Moderate Stone fruits/Nuts Crown gall {Almond (wild peach, bitter almond, behmi} 10-35 Jindal and Sharma (1988) Severe Crown gall Peach(wild peach) 10-60 Jindal and Sharma (1988) Severe Crown gall Cherry 5-15 Jindal and Sharma (1988) Severe Crown gall (Plum or apricot) 5 Jindal and Sharma (1988) Severe Rust 10.3-77.6 Thakur and Xu (2004) Severe Stigmina blight 91.06 Sharma and Gupta, (1988) Severe Leaf curl ---- - Severe Frosty mildew ------- - Moderate Incidence and present status of various diseases in India
- 6. •Apple scab is the most serious and damaging disease of apples in the world (Gianessi and Williams, 2012. International Report). •In India, the total loss caused by apple scab may exceed that caused by all other pests and diseases combined (Anonymous, 2000). • In epidemic years, apple losses have been as high as 70% . •Major outbreaks of apple scab in India in the late 1970s and early 1980s. •The disease was reported in Himachal Pradesh in 1977 and in 1982- 83 severe epidemic occurred.
- 8. Apple scab is also known as black spot in England, Australia and South Africa. In North America the disease is known by apple scab.
- 9. •Attack of apple scab caused the loss of 80 percent of his crop. Trees badly weakened resulted in low yields in later years. Because of their poor condition, 15 percent of the trees died during drought. Even 20 years afterward, the orchard had not returned to its original healthy, profitable state. But that is not all? •The financial setback forced the farmer to borrow heavily every year in order to produce a crop. As a result, the farm became so debt-ridden that he would gladly have sold it for the amount of indebtedness. In order to make a living, he had to seek outside employment and finally became a full-time worker at another occupation. Thus one bad attack of a plant disease turned a debt-free enterprise into a liability. Economic Loss associated : a case study of a farmer of Pennsylvania, USA
- 10. Biology • The apple scab disease evolved along with the apples. • Caused by the fungus Venturia inaequalis (Cke.) Wint., anamorph Spilocaea pomi Fr. (Hughes, 1953). • The summer stadium of the disease was first described by Fries, 1819. • The winter stadium was illustrated by Cooke (1866). • The fungus is placed in the division Ascomycota, order Pleosporales and family Venturiaceae. • The major characteristic is the one-septate green, yellowish, or olivaceous-brown ascospore (Barr, 1968). • The perfect state involves formation of a pseudothecium, which is seen as black pin-point heads on the over-wintering apple leaves. • Within this pseudothecium the asci are formed; each ascus contains eight ascospores. • Sivanesan & Waller (1974) state the size of ascospores as 12-15 x 6-8 μm.
- 16. Pathogenesis • V. inaequalis has a hemibiotrophic life cycle characterized by a saprophytic phase in autumn-winter and a parasitic phase in spring- summer. • The fungus passes the winter in the old fallen leaves as immature pseudothecia (fruiting body). • Ascospores constitute the primary source of inoculum. • Inoculation is brought about through the agency of the wind.
- 17. • For infection, ascospores and conidia have to land on a young leaf or fruits of a compatible cultivar and need a water film to germinate. • The ascospores are discharged into the air from the old leaves on the ground. • Spore discharge is conditioned by – (1) the maturity of the ascospores themselves. – (2) The occurrence of rain-periods when the ascospores are mature. – (3) Ascospores are also discharged by light. It has been estimated that 45 minutes of wet period at optimum time is enough to discharge eight billion ascospores from the fallen old leaves under a large apple tree. These ascospores require several hours of rainy conditions for germination. Within a few days, the pathogen establishes a food relation with the host (Hesler 1917).
- 18. Apple scab-infected leaf litter
- 19. Apple scab races 1-7. Sources: Janick & Moore (1996); Roberts & Crute (1994). Race Source Susceptible material 1 Worldwide Most of the world´s cultivars 2 South Dakota, USA M. baccata, 'Dolgo', 'Alexis', 'Bittercrab' segregates of R12740-7A, 'Geneva' 3 Nova Scotia, Canada 'Geneva' 4 Lafayette, Indiana, USA Segregates of R12740-7A 5 Norwich, England M. micromalus pit type resistance, M. atrosanguinea 804 6 Ahrensburg, Germany 'Prima' (Vf cultivars) but not 'Evereste', M. x 'Perpetu' and M. flori The last race to be discovered was the English race or race 7, which was described by Roberts & Crute (1994) . An isolate from a naturally infected M. floribunda tree gave lesions on M. floribunda 821 and some Vf cultivars while some other Vf cultivars were not infected. Later a second dominant gene was discovered in M. floribunda 821 (Vfh) and the host-pathogen relationship was discussed. It was confirmed that 'Golden Delicious' (Vg) was resistant to race 7 (Bénaouf & Parisi, 2000).
- 20. Symptoms • First on underside of the emerging cluster leaves. • Lesions can vary from very few to several hundred per leaf. • Sheet scab- entire leaf surface is covered with disease. • Pin-point scab-infection occur late season, not detectable until harvest. • Storage scab- incipient infection, too small to see prior to fruit storage, due to sporulation from older lesions. Sheet scab- Pin-point scab-infection
- 21. At first, spots are velvety and olive green with indefinite margins. Can occur on upper or lower leaf surface. Old leaf harbouring apple scab lesions for the next years epidemic
- 22. Later, spots turn brown to black; margins become more definite. Leaves turn yellow or brown; trees can defoliate prematurely.
- 23. At first, spots on fruit similar to spots on leaves. Later, spots turn corky and brown. Spots are superficial, but can cause fruit cracking.
- 25. Genetic improvement for introgression of resistance • Most of present day cultivars are susceptible to apple scab disease and fruit growers have to spray 15 times with fungicides in a season. • Wild species of Malus are resistant to the scab disease (Soriano et al. 2009) and can be good sources of transfer of scab resistance to high quality susceptible cultivars. • Thus, there is an urgent need for genetic improvement of apples for scab resistance. • It can be achieved in three ways, i.e. – by making sexual crosses of selected apple genotypes, – by mutation breeding, and – by addition of genetic material through genetic modification.
- 26. Introgressing genes from related species Genes for resistance to scab have been identified in collections of apples and related species made in Uzbekistan, the center of origin of this crop.
- 27. Apple scab resistance genes and plant sources for resistance genes. Sources: Lespinasse, 1989, 1994; Bénaouf & Parisi, 2000; Hemmat & Brown, 2002. Monogenic Polygenic Symbol Species/selection Species/selection Vf M. floribunda M. baccata Vfh M. floribunda 821 (selected seedlings) Vm M. micromalus M. sargentii 843 Vr M. pumila R12740-7A M. sieboldii 2982-22 (stellate necrotic) M. x zumi calocarpa Vbj M. baccata jackii M. toringo 852 Vb Hansen´s baccata #2 Old European cultivars Va 'Antonovka' PI 172623 Vg 'Golden Delicious' Vx M. pumila R12740-7A (pit type) Unfortunately the Vf-cultivars have so far had limited commercial success. One reason is that the acid taste from M. floribunda is still present in the final cultivar. The taste and overall quality have not been high enough to compete on the market.
- 28. Conventional breeding • by artificial pollination of selected genotypes with pollen from selected donors. • some bottlenecks concerned with the conventional breeding of apple. – Firstly, development of a variety takes a lot of time as the juvenile period is very long i.e. four to ten years (Ibanez and Dandekar 2007). – Secondly, during crossing along with the trait(s) of interest other undesirable traits may be introgressed which is referred to as “genetic drag”. • In order to improve the quality of the genetic material it is necessary to perform sequential crosses with elite material for several generations, because apple is self-incompatible and one cannot perform backcrosses with one high-quality parent (Schouten et al. 2009).
- 29. • In 1914 crosses were made for introduction of resistance to apple scab into commercial apple varieties, using the crab apple Malus floribunda 821 as a source of resistance (Crandall 1926). • Approximately 85 years after the first cross, Vf- cultivars with a good fruit quality were introduced onto the market, – e.g. the varieties ‘Santana’, ‘Topaz’, ‘Florina’ (Bakker et al. 1999).
- 30. Repeat backcross to M. domestica several times to recover most of the traits found in the regular apple while also selecting for resistance to apple scab disease. Each generation will take several years. M. floribunda crabapple resistant to scab M. domestica cultivated apple susceptible to scab F1 Select scab resistant plants M. domestica Backcross BC1 Select scab resistant Plants with large fruit M. floribunda crabapple resistant to scab M. domestica cultivated apple susceptible to scab
- 31. Releases of scab-resistant apples. PRI releases Year released 1. Prima 1970 2. Priam 1974 3. Priscilla 1972 4. McShay 1988 5. Sir Prize 1975 6. Primiera 1995 7. Jonafree 1979 8. Nambu 1994 9. Redfree 1981 10. Constance 1995 11. Dayton 1988 12. Primivera 1996 13. Williams’ Pride 1988 14. Juliet 1999 15. Enterprise 1993 16. GoldRush 1993 17. Pristine 1994 18. Scarlett O’Hara 2000 19. Pixie Crunch 2004 20. Sundance 2004 21. CrimsonCrisp 2005
- 32. Highly susceptible ‘McIntosh’; ‘Vista Bella’ Susceptible ‘Cortland’; ‘Red Cortland’ (RedCort); ‘JerseyMac’; ‘Jonamac’; ’Lobo’ Moderately susceptible ‘Early Geneva’; ‘Empire’; ‘Golden Delicious’; ‘Jonagold’; ‘Lodi’; ‘Mutsu’; ‘Northern Spy’; ‘Spartan’; ‘Royal Gala’ Low susceptibility ‘Golden Russet’; ‘Idared’; ‘Red Delicious’; ‘Sunrise’; ‘Paulared’ Resistant ‘Belmac’, ‘Enterprise’, ‘Freedom’, ‘Florina’ (Querina), ‘Jonafree’, ‘Liberty’, ‘Macfree’, ‘Nova Easygro’, ‘Novamac’, ‘Primevere’, ‘Pristine’, ‘Redfree’, ‘Richelieu’, ‘Rouville’, ‘Supermac’
- 35. • only Vf has been positionally cloned (Vinatzer et al. 2001). • Vf proved to be a gene cluster with four paralogs; – HcrVf1, – HcrVf2, – HcrVf3 and – HcrVf4 (Xu and Korban, 2002). Malus floribunda proved to be a good source of natural scab resistance genes. The genes HcrVf1 andHcrVf2, consisting of promoter, coding and terminator sequences in their natural configuration. Biotechnology for faster resistance breeding In view of time and genetic drag, improvement of apple through genetic modification is an alternative option.
- 36. Leaf symptoms 21 days after inoculation with V. inaequalis conidia. Transgenic line Ga2-21 (Upper Right), containing HcrVf2, represents typical symptoms observed on all HcrVf2 transformed lines. Transgenic line Ga2-7 (Lower Right) contains only the selective nptII gene and is thus a transgenic control. The susceptible cv. Gala (Lower Left) and resistant cv. Florina (Upper Left) are included for the comparison of scab symptoms.
- 37. Disease forecasting • The Mills curves, published in 1944, were the first attempt at using forecasting to help growers time the application of sulfur dusts. • Mills curves relate the hours of leaf wetting and temperature during a wetting period to the likelihood of scab infection (Sutton 1996). • First fungicide spray is applied during the first predicted infection event and subsequent applications are applied relative to the residual activity of the pesticide and other predicted infection events.
- 38. Mills Units • light infection period required at least 3 days more for the development of scab symptoms at a leaf wetness duration of 9.0- 13.4 hr and at an average temperature range of 8.5-21.4°C, • moderate and severe infection periods (>15.0 hr leaf wetness) required 1 more day to exhibit symptoms. • The rescheduling of fungicide applications on the occurrence of infection periods revealed that at least 3 sprays could be saved to control the scab diseases below the economic threshold. • forecasting and monitored spray programmes may be devised in accordance to the prevailing weather conditions of the region.
- 39. Forecasting: Prediction of probable outbreak or increase in disease intensity under a particular set of environment Lies in helping growers to avoid financial losses –Caused by reduced yields - Fungicides are more effective if growers apply when infection starts or just prior to it –Caused by unnecessary - and costly - pesticide sprays Lies in minimizing environmental hazard/consumer concern Applying Pesticides when there’s no threat - isn’t cost effective, Not Applying Pesticides when there is a threat - isn’t economic gain,
- 40. Main reasons of disease forecasting – why to forecast ? Reduce unnecessary dependency on fungicides Economic issue - Reducing cost of production - timely application of control measures/ fungicides. Only when required, (usually start of epidemic) - Avoids unnecessary/ wastage of fungicides Safety target - Economic Safety covers crop – reducing possible phototoxic & environment effects Reducing exposure to non-target species, operators & consumers. Countries target to reduce pesticide loading – Organic aspects Justified use - Consumer demand for pesticide – free produce, Seeking justification for their use. Use of PDF schemes provide that justification. It is important for growers to monitor conditions carefully in their area to evaluate the potential need for fungicide applications.
- 41. Current status of Plant disease forecasting in some countries These systems provide: Back ground information on the disease, current management recommendations, disease forecast information based on host, pathogen, and environmental factors important for making an accurate forecast. Current examples: Apple scab, Fusarium head blight of wheat and Asian soybean rust. Daily information on-line are available for various diseases
- 42. Methods of disease forecasting 1.Forecasting based on primary inoculum Presence of primary inoculum, its density and viability of spores or propagules determined in air, soil or planting material. - using air trapping devices or laboratory examination. 2.Forecasting based on weather conditions Temp., RH, rainfall, leaf wetness, light, wind velocity etc., (winter/ crop season). Weather stations with sensors to record fluctuations for infection Period. 3.Forecasting based on correlative information Weather data of several years collected and correlated with the disease intensity. Forecasting criteria developed from comparisons of disease observation with standard meteorological data - Data compared and then forecasting done. (Apple scab, Septoria leaf blotch of wheat, fire blight of apple, etc.) 4.Use of computer for disease forecasting In many countries forecasting of disease is made using computers.
- 43. Automated or electronic apple scab predictors • Based on –temperature, rainfall, relative humidity • Most common are- – Modified Mills (Jones et al., 1980). – Ventum (Butt et al 1992). – ADEM (Butt and Xu, 1996) – RIMpro (Trapman and Polfliet 1997)
- 46. RIMpro Scab forecasting model RIMpro (Relative Infection Measurement Program) is the first scab forecasting model of a new generation. predicts the maturation process of overwintering scab lesions as the basis of its forecast. Mature ascospores are released during periods of rain if light and temperature regimes are met. Severe infections occur if a high inoculum load is discharged and the conditions are suitable for infection. Less severe infections will result if spore discharge is reduced or if infection conditions are suboptimal. RIMpro-scab simulates these processes on the basis of weather data, providing a clear graphical display.
- 47. What data does RIMpro need ? • RIMpro needs measurements in at least 1 hour intervals, better 30 or 15 minute readings. • The following measurements are needed: -Temperature °C • Air humidity % • Precipitation resolution 0,2 mm • Leaf wetness Yes-No, % , • or time in interval *)
- 48. RIMpro-Foerecast for apple scab under evaluation in Kashmir (Site Shopian) Infection on fruits Infection on leaves
- 49. Spread and progress of V. inaequalis infection at varying isolation distances of apple from inoculum source (Kashmir)
- 50. Automated weather stations at various locations of the valley Deltas-T, UK
- 51. Requires the examination Two false predictions: (Economic effects) False negative predictions → in which a forecast made for a disease not to occur, when in fact the disease was found False positive predictions → in which a forecast made for a disease, when in fact no disease was found in a location (Yuen, 2006; Madden, 2006)
- 52. Major obstacle in disease forecasting Validity of models Accuracy of weather information - could be improved Temp. rarely constant; creating a situation – infec. interval not flagged (low av. temp.) but actual temp. during a portion of wet. period sufficient for infection. Need for continuous and systematic effort to develop better models. Attempts should be made to establish a network for testing and model comparison. Information delivery system - applied to forecast other diseases and insects pests by changing PDF models in program server. Forecast systems , in conjunction with geographical information systems, can be used to generate maps to illustrate disease development over fruit belts in the country.
- 57. Control measures • Apply 5% Urea to fallen foliage to increase the speed of microbial decomposition of the leaves. • Avoid wetting the foliage when irrigating lawn or groundcover. • Irrigate in the morning so the sun will reduce the amount of time the leaves are wet. • Prune trees to open up canopy to allow good air circulation and reduce amount of time leaves are wet
- 58. Chemical Controls • Fungicides used for control of Apple Scab are either preventive and/or curative. • Preventive fungicides must be applied before an infection period, whereas those fungicides that are curative should be applied after an infection period but must be within the time period suggested by the manufacturer.
- 59. Spray fungicides on susceptible varieties: – start when leaves show 1/2 inch new growth. – most garden store fungicides are protectants and must be applied before infection. – if spring weather is wet, reapply fungicide every 10-14 days.
- 60. SPRAY SCHEDULE---2017 TREE STAGE CHEMICAL Qty. for 200 Lts. Water DISEASE CONTROLLED Green Tip Captan or Ziram or Dodine 600 g or 600 ml 200 g Scab Pink Bud Mancozeb or Difenconazole 600 g or 30 ml Scab Petal Fall/ Pea Size Thiophenate Methyl/Hexaconazole/ Flusilazole 100 g or 100 ml ml 50ml Scab Fruit development (Walnut stage) Myclobutanil or Mancozeb or Propineb 80 g or 600g or 600g Scab Fruit development (20 days after 4th spray) Dodine or Propineb or Zineb 150 g 600g or 600 g Scab Pre Harvest(20 to 25 days before harvest) Captan or Ziram 600 g or 600 ml Scab, Fly speck & Sooty Blotch
- 61. Use a Drones to Fight Against Apple Scab For apple growers in the eastern United States, the biggest problem – the most relentless, pervasive, unavoidable issue, which can ruin a whole crop if not managed aggressively – is apple scab. Researchers at the University of New Hampshire are working on a new tool to combat the apple scourge: A drone.
- 65. Conclusion • Apple scab is one of the dreaded disease of apple cause largest economic loss. • Resistant varieties are still lack in fruit quality traits. • Chemical Control measures are available and highly effective. • Excessive use of pesticides is always creates residual toxicities and reduces farm returns.