Aerobiology and epidemiology of apple scab in Central Himalayas of India
K. P. Singh,J. Kumar, R. K. Prasad*,A. Singh, *Dinesh Prasad* and R. P. Singh
Department of Plant Pathology, College of Agriculture, G B Pant University of Agriculture & Technology, Pantnagar, UdamSingh Nagar, *College of Forestry, UUHF, Bhasar, Uttarakhand
Apple Scab, caused by Venturia inaequalis (Cke.) Wint. (anamorph Spiloceapomi Fr.), is considered to be one of the most important fungal diseases of apple, which occurs almost every year in severe epidemic form under favourable environmental conditions wherever apple is cultivated. In India, the disease causes significant economic losses in the states of Jammu & Kashmir and Himachal Pradesh each season, and has been prevalent in Uttaranchal hills, the 3rd largest apple growing state in the country. In India, the disease causes significant economic losses in the states of Jammu & Kashmir and Himachal Pradesh each season, and has been prevalent in Uttarakhand hills, the 3rd largest apple growing state in the country. Yield losses during epidemic years in 1996, 2008 and 2013 in the Bhatwari fruit belt of Distt. Uttarkashiwent up to 84 per cent (Figure 1). The main reason for the heavy infection appeared to be the high inoculum level from the previous season. Continuous wetting periods resulted in moderate to heavy infection in orchards with high infection potential during the summer period of the growing season Weather conditions especially rainfall, duration of leaf wetness and temperature vary at different altitudes in the Himalayan region, where apple is cultivated. Therefore, understanding the timing and intensity of environmental conditions that trigger ascospore release may provide useful information to growers who use fungicides to protect their trees from new infection. Thus, the objective of this study were: (i)to find out thepre leaf fall spray of chemical, cow urine and fungal antagonists on spring ascospore production (ii) to identify the pattern of primary inoculum of V. inaequalis in farmers’ orchards at varied apple growing regions of Uttaranchal hills (ii) to ascertain the relevance of Mills infection period for predicting apple scab infection periods, (iii) to find out the relation of degree-day accumulation to predict the beginning and the end of the ascospore maturation (iv) to determine potential ascospore dose from farmers’ orchards at Gangotri valley in Uttarankhand Himalayasand (v) to manage the storage decay fungi of apple with chemicals and antagonists.
In Bhatwari fruit belt, defoliation in apple trees started around mid August and continued for nearly 65 days. Maximum leaf fall (82%), however, was observed during the period October 15th - November 15th after which trees were completely defoliated. A scabbed leaf collected on 30 April was the most effective date that resulted 25 percent partial decomposition. The partial decomposition rate was observed low in the month of May with collected leaves on 30 Dec. (0.37 %), 30 Jan. (3.51 %), 28 Feb. (9.76%), and 30 March (18.01 %) at Jochira, Gangotri Fruit valley of District Uttarkashi, Uttarakhand. The present findings reveal significant relationship between the time of leaf fall and leaf decomposition, which plays important role in maturation and discharge pattern of ascospores. The leaves which fell earliest in the season, showed maximum reduction in leaf weight and area. It could therefore concluded that earlier the leaf fall better the decomposition of apple leaf litter during the over wintering stage. Eighteen micro-organisms were isolated and identified to parasitize saprophytically on apple leaves but only four isolates namely, Athelia bombasina, Trichoderma harzianum, Chaetomium globosum, and Myrothecium roridum were further evaluated for their effect on reducing primary inoculum of V. inaequalis. A single pre-leaf fall spray of 5 % urea was significantly decomposed the over wintered leaves, and were on par or superior in effectiveness as compared to the 100 % cow urine, antagonists and Carbendazim. Similarly, the application of urea at 3 and 5 percent was significantly proved better over others for reducing the pseudothecial formation (97.31, 78.72 %) and the discharge of ascospores (98.04, 95.66 %) from over wintered leaves. Among the four antagonists, A. bombasina was highly effective in reducing the development of pseudothecia (69.57%) and ascospore productivity (84.31%).The application of Sterol-biosynthesis inhibiting fungicides at a lower dose gave maximum (83 to 89 %) inhibition of ascospores discharge as compared to other fungicides was also recorded. This study indicated that urea/ antagonist (Athelia bombasina) spray could be safely applied during leaf fall stag of apple tree and orchard floor for the management of primary inoculum of V. inaequalis
The formations of pseudothecia and ascospore discharge were associated mainly with late autumn (October) infection. The maximum pseudothecia and ascospore production was observed in the 1996,2008 and 2013and least in 2001 and 2002. Maximum ascospores productivity was recorded at petal fall and fruit set stage of apple with ascospore productivity of 1, 31,250/ml and thereafter declined gradually. In most of the years, the relationship between ascospores productivity and primary infection of scab was found to be much higher (>90 %). The pseudothecial formation takes 32 to 48 days more after sexual reproduction at temperature around 8 to 10°C and this process completes between January to February every year in Garhwal Himalayas. The observation revealed that 96 per cent pseudothecia were mature at green tip stage during 2nd week of March at Purola-Naugao, Tuni-Chakarata, and Tal-Talwari fruit belts (1700-2000 m asl) while at Bhatwari and Auli-Joshimath fruit belts (2100-2600 m asl) the pseudotheciastarted becoming mature at late pink bud stage. The ascospore emission period was 61-76 days and mean numbers of cumulative degree days for 50 and 85 per cent spore release from these observations were 456 and 960.
Ascospore maturation peaked between pink bud and fruit set stages and was completed by fruit set stage or shortly thereafter (6 – 10 meteorological weeks). To improve spraying efficiency with reduced fungicides use, reliable scab warnings are helpful. Weather data were recorded using microprocessor-based orchard environment monitor, RSS – 412 apple scab predictor and µMETOS scab warning device. The total infection periods were observed in each year periodically from March till August at the Gangothri valley area of Uttarakhand. Data accumulated over 10 years were analyzed for validation of Mills criteria to establish its relevance in rescheduling fungicide applications under monitored spray programme. On examination of the primary infection period of 17 years data from Bhatwari fruit belt, some differences were observed between our results and Mills table for ascospores infection. The observation revealed 2 day (light infection), 1 day (moderate infection) and 1 day (severe infection) delay in symptom expression under orchard conditions. The regression analysis was used to describe relationship between Mills infection criteria and our light, moderate and severe infection period data of Uttarakhand hills for symptom appearance in orchards.
The environmental conditions varied from location to location, and Mills infection periods ranging from 19–47 were recorded from April to September every year revealed that number of infection periods varied from year to year depending upon the weather conditions. The Mills infection criteria for predicting primary infection has been widely adopted with modifications to suit local conditions.The observation revealed 2 day (light infection), 1 day (moderate infection) and 1 day (severe infection) delay in symptom expression under orchard conditions.
At present, PAD is a useful tool to forecast the total amount of inoculum in an orchard and has been shown to effectively improve apple scab management. We studied different inoculum levels under Garhwal Himalayan conditions, where reduced spray program could be used after
Figure 1. Scab incidence in leaves and fruits of apple in Bhatwari fruit belt over years.
petal fall for the management of scab. PAD, that has great impact on disease development in the following season, varied from 512 to 635056 in the various orchard of Bhatwari fruit belt. The PAD value was low during 1999 to 2001 (612 – 2192 ascospore/m2) and medium during 2002-2006 (4262 - 37848 ascospore/m2) due to the fact that the springs were early, dry and not more favorable for ascospores maturation. In 1996, 2008 and 2013, the PAD values were high because of the favourable weather conditions and increase of inoculum accumulation. The scabbed lesion and leaf litter density were approximately more than twice in Bhatwari fruit belt in 1996 2008 and 2013. PAD involves the elimination of unnecessary early-season sprays in orchards where the inoculum is below a specified level. PAD values were 50 times higher in the poorly managed orchards than in the integrated managed orchards. Warnings are issued mainly via a call in telephone, Agriculture Govt. department, and broadcasted through radio stations. The IPM programme reduced the cost of fungicide treatments by 38 percent as compared with disease control practices currently used by commercial growers in Uttarakhand. The possibility of an integrated approach to control the diseases menaces would be discussed.
Three important commercial cultivars of apple namely, Red, Royal, and Golden Delicious were screened against post-harvest rot causing fungi. The major fungal pathogens Trichothecium roseum, Penicillium expansum, Glomerella cingulata, Botrytis cinerea and Monilinia spp. were responsible for fruit decay in storage. Red Delicious was recorded to be highly susceptible to most of the post-harvest pathogens. Post harvest sprays of flusilazole (0.015%) bitertanol (0.075%) and carbandazim (0.05 %) were effective in controlling storage scab and other rotting fungi. Biocontrol agents effective against P. expansum and B. cinerea were isolated from apple leaves, and a quantitative relation between antagonists and pathogens inoculum concentration was determined.
Biography
Dr. Singh has completed his PhD in 1990 under supersion of Dr. Udai Pratap Singh from Banaras Hindu University. I am working as a Professor in the Department of Plant Pathology, College of Agriculture, G B Pant University of Agriculture and Technology. My current research work focuses on the application of orthodox tools of Plant Pathology in epidemiology with forecasting approaches for Management of Plant Diseases of different nature of different crops for sustainable living and development of the society. Dr Singh has published more than 50research papers in reputed journals and has been serving as an editorial board member of reputed journal.
Presenting author details
Full name: Krishna Pratap Singh
Contact number:00919412142537
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Session name/ number:Crop Protection & Awareness
Category: Oral presentation