By Syed Adeel Sajid1 and Bilal Akram2
(1Department of Plant Pathology, 2Department of Horticulture, College of Agriculture, University of Sargodha)
Cherry fruit is a fleshy drupe containing a stone in the center surrounded by a fleshy part. Nutrient rich fruit with comparatively low caloric content. It also comprises of substantial amounts of important nutrients including fiber, polyphenols, carotenoids, vitamin C, and potassium. Cherries are also good source of tryptophan, serotonin, and melatonin. There are two major categories: tart and sweet cherries, or Prunus cerasus L. and Prunus avium L., respectively. Their colors can vary from yellow to deep blackish-red. Fruit of hilly areas needs low temperature and several chilling hours for quality fruit. In Pakistan, cherries are cultivated in the Northern areas, Gilgit-Baltistan and Baluchistan. According to FAO (STAT.), production of cherry in Pakistan was 2206 tons in 2017. Cherries are used for frozen pies and pie filling and for canning, bakeries, ice cream, sauces, preserves and other deserts.
Cherries are a rich source of polyphenols and vitamin C which have antioxidant and anti-inﬂammatory properties and great for healthy skin, strong tendons, ligaments, blood vessels and cartilage. These delicious fruits also provide a small amount of zinc, iron, potassium, manganese and a magnanimous helping of copper. Potassium helps regulate heart rate and blood pressure. The boron in cherries helps increase bone health as part of a magnesium and calcium enriched diet.
Postharvest losses and decay:
Postharvest diseases develop on fruit and other plant products after harvesting during grading, packing, during transit, transportation to market and consumer and while the produce is in the possession of the consumer until the moment of actual consumption. The plant products may show the symptoms of the diseases that began in the field but remained latent. The pathogenic organisms secrete toxic substances that make the product or its part unfit for consumption. Pathogens causing postharvest diseases attack healthy and living tissue which they disintegrate and cause to rot.
Cherries are highly perishable and demand care to handle after harvest. In developing countries, postharvest losses are often more severe due to inadequate storage and transportation facilities. In Pakistan, almost 20 to 30% of cherry is lost due to postharvest management and diseases. The main postharvest pathogens are of fungal origin like molds. The fungal inoculum arrives into the pack-house with the hard vdvested fruit, on its surface, in disease fruits, on contaminated tools and bins and with orchard litter. Cracks in cherries act like wounds due to mishandling, insects, rodents and farm tools act as entry points for fungal spores to enter the fruit and proceed to decay the fruit. The extent and nature of damage depends on the picking conditions, handling, type of product, disease organism and storage conditions.
Environmental conditions of produce play an important role in development of infection by the pathogens following postharvest wastage of the produce. Factors like temperature, moisture, composition of CO2 and O2 seriously affect the initiation of infection and development of symptoms. Storage temperature is so critical for controlling postharvest diseases. High temperature and humidity favour the development of postharvest decay in cherries. Ripe fruits are more susceptible to invasion of pathogens and some pathogenic fungi most likely to invade after the fruit is completely ripe or has become senescent.
Postharvest pathogens of cheery include Penicillium spp., Botrytis cinerea, Monilinia spp., Cladosporium spp., Rhizopus stolonifer, Alternaria spp. and bacteria such as Erwinia and Pseudomonas.
Major Postharvest Diseases of Cherry
- Alternaria Fruit Rot:
Alternaria fruit rot also known as sooty mold and dark spot disease caused by Alternaria alternata. Infection starts when fungus takes entry through wounds and producing dark brown circular spots. Later on, as the disease proceeds, the spots coalesce to form lesions containing concentric circles of spores. Fruits become wrinkled with dark lesions. A. alternata has been regarded as the major mycotoxin-producing specie in Alternaria spp..
- Gray Mold:
Gray mold is a devastating disease of fruit during postharvest caused by Botrytis cinerea. This pathogen may produce disease symptoms in the pre-harvest period or remain quiescent until post-harvest period. The annual economic losses of B. cinerea easily exceed $10 billion worldwide. It has both asexual stage (conidia) and sexual stages (sclerotia) to survive in favorable or unfavorable conditions. Infected fruits turn gray-white, soft and rot. A mass of grey-brown conidia produces on brown lesions.
- Olive-green Mold:
This mold of cherry is caused by Cladosporium herbarum so also known as Cladosporium Rot. Spores of this fungus enter the fruit through breaks in the skin, and proceed to decay the fruit. Fruit tissues become hard, decayed with grey to black discoloration.
- Brown Rot:
Brown rot is caused by the ascomycete fungus Monilinia fructicola and is an important pathogen on cherry. The pathogen can infect fruits directly without the need for wound. The fungus attacks fruit as well as other plant parts. In ideal environmental conditions, due to its fast-reproductive cycle pathogen initiate epidemic inoculum levels in as little as 24 hours. In start, dark spots develop on fruits and later on coalesce with each other. Fruit wrinkles and covers with brown conidial sporulation (mummy) and mostly fall onto the ground. Fungus overwinters in the mummified fruits, which serve as sources of inoculum for the coming season.
- Rhizopus Rot:
This disease is also known as watery white rot because fruit tissues become watery and a profuse production of coarse white fungal strands with black spore heads (sporangia). Rhizopus rot which is one of the most severe postharvest diseases of cherry caused by Rhizopus stolonifer a typical postharvest pathogen. Rhizopus rot enlarge rapidly and can involve the entire fruit in 24 to 48 hours.
- Blue Mold:
Blue mold is caused by an important postharvest pathogen Penicillium expansum. The fungus is characterized by the blue-green velvety sporulation covered by white expanding mycelium therefore called as blue mold. At early infection stages, blue mold symptoms include light tan to dark brown circular lesions with very sharp margin between diseased and healthy tissues. Decayed fruit has an earthy, musty odor. The fungus can grow at temperatures as low as -3ºC (27ºF) and germination can occur at 0ºC (32ºF).
All diseases either postharvest or pre harvest diseases can be controlled by proper handling and good agricultural practices which involves cultural practices and timely and perfectly harvest to counter postharvest diseases.
- Cultural Practices
- Careful handling, removal of damaged fruit, and rapid cooling are effective methods of decay management for these diseases.
- Wounding to the produce can be minimized by careful harvesting, sorting, packaging and transportation, including preventing the fruit from falling at all stages.
- Eradicate crop debris that may serve as sources of inoculum.
- Hydro-cool cherries as soon as possible after harvest.
- Physical Practices
- These diseases may be controlled by various physical treatments, such as, low temperature storage, high temperature treatments, magnetic fields and radiation.
- Hot water treatment of 52ºC for 2 minutes is effective for controlling cherry rots.
- Hot air treatment at 44°C for 114 minutes is effective in inducing disease resistance and suppressing blue mold decay in cherries.
- Preharvest treatment of cherry fruits with 2mM salicylic acid and 0.2mM methyl jasmonate is significantly effective to reduce brown rot.
- Preharvest application of iprodione at 1.13 kg a.i./ha with a postharvest dip in a suspension of C. infirmo-miniatus containing 0.5 to 1.5 × 108 CFU/ml. is effective for control of brown rot.
- Chemical Treatments
- Dicloran and Iprodione are effective against Rhizopus spp.
- Imazalil is good for managing Alternaria rot.
- Thiabendazole & Carbendazim are effective against Brown rot, Blue mold and Gray mold.
- Benomyl, Thiophanate-methyl, Captan, Chlorothalonil + Sulfur, DCNA, Sulphur are also effective as chemical treatments for Brown rot.
- Biological Control
- A bacterial strain Bacillus subtilis by producing antibiotics significantly control Brown rot and Gray mold of cherry.
- Enterobacter aerogenes is effective against Alternaria rot.
- Antagonistic yeasts, Trichosporon pullulans, Cryptococcus laurentii, Rhodotorula glutinis, and Pichia membranefaciens are effective against several of the main postharvest pathogens on sweet cherries at 25◦C.