30 Oct Capsicum Phytophthora Blight Management in an Integrated Way
एकीकृत तरीके से कैप्सिकम फाइटोफ्थोरा ब्लाइट प्रबंधन
Capsicum (Capsicum annuum L.) is a widely cultivated vegetable crop all over the world. It is known by common names viz., bell pepper, green pepper, capsicum and vernacular name, Shimla-mirch in Hindi. It is one of the popular vegetables extensively cultivated throughout India especially in hills during summer months and as autumn crop in Karnataka, Maharashtra, Tamil Nadu, Bihar, West Bengal and Madhya Pradesh.
Capsicum is affected by broad range of pathogens and insects that includes fungi (Phytophthora capsici, Rhizoctonia solani, Verticillium dahliae, Colletotrichum spp., Leveillula taurica and Fusarium spp.), bacteria (Xanthomonas spp.), viruses (Tospoviruses, Potyviruses, Tobamovirus and Cucumoviruses), nematodes (Meloidogyne spp.); and insect pests (aphids, lepidoptera and thrips).
Among diseases, Phytophthora blight incited by Phytophthora capsici Leonian is the most devastating field diseases of capsicum worldwide and in India.
Where is the disease economically important?
Phytophthora blight incited by Phytophthora capsici Leonian was first reported on chili pepper (Capsicum frutescens) in New Mexico in 1922. Globally the disease and pathogen are widely distributed and has been reported in all the major pepper production areas. It is reported to cause crop losses exceeding 50 per cent.
In India, the Phytophthora blight disease was first reported in 1971 from Solan, Himachal Pradesh on capsicum and paprika. At present P. capsici is reported in clusters in the states of Kerala, Karnataka, Himachal Pradesh, Jammu and Kashmir and Tamil Nadu.
Apart from this it is reported in one place each in Andhra Pradesh and West Bengal on different crops. As per invasive species compendium of CABI, the species is of restricted distribution in India .
Symptoms of Phytophthora blight
Seedlings damping-off, root rot, collar rot, crown rot, leaf blight, stem rots, fruit rot and wilt are the major symptoms observed in capsicum with P. capsici infection.
In seedlings, damping off associated with root-rot can kill plants. In older plants, root infections can result in stunting, wilting, and eventual plant death in approximately two weeks.
The root-rot syndrome caused by P. capsici is associated with root darkening and small lesions that can quickly expand to girdle and kill the root.
On leaves, the disease initiates as a small circular or irregular-shaped lesion giving a “scalded” appearance. Infected leaves eventually turn brown or tan and may defoliate as infection spreads to the stem.
The disease progresses to the stem causing stem blight. Stem-blight appears as a dark-green and water-soaked lesion, later causing stems to dry and brown. Crown-rot symptoms include distinctive black or purple lesions near the soil line.
The lesions rapidly coalesce and girdle the main branches of stem, which results in stem or entire plant death. On fruit, rot appears as brown lesions which elongate with whitish sporangial mass under favorable conditions. The infected fruit becomes dry, sunken, and mummified.
Pathogen and disease cycle
Phytophthora blight of capsicum is caused by the pathogen, P. capsici Leonian (1922). It is placed in Kingdom Chromista, along with some algae, diatoms and protozoans. Phytophthora blight of capsicum is a poly-cyclic disease.
Under favourable conditions, repeated complete infection cycles occur in few days. Many overlapping cycles occur simultaneously during periods of favourable weather.
The pathogen survives as oospores in soil. Oospores possess thick walls that allow them to survive harsh environmental conditions.
Under favourable conditions, oospores germinate directly to produce germ tube or indirectly to produce sporangia on sporangiophores. Sporangia can dislodge from sporangiophore and spread by wind, air and irrigation water.
Mature sporangia may germinate directly via formation of one to several germ tubes or germinate indirectly by releasing 20-40 motile biflagellate zoospores under conditions of free moisture on plant surface or in soil.
Zoospores are able to swim for several hours and infect plant tissues. To reach their target, zoospores respond to various molecular, chemical and electrical stimuli. Zoospores first lose their flagella and then encyst and form a cell wall, germinate and infect plant tissues.
Abundant sporangia are produced on infected tissues, particularly on affected fruit serves as secondary source of inoculums to initiate polycyclic disease. The pathogen survives on other alternative hosts and in soil as oospore inocula.
Integrated management schedule
An integrated schedule for management of Phytophthora blight in capsicum was evolved and validated based on field studies at ICAR-Indian Institute of Horticultural research, Hesaraghatta Bengaluru with following interventions;
Cropping sequence:
Phytophthora blight is a broad host range pathogen. Crop sequence patterns should take in to account this host range information so as to reduce pathogen survival and perpetuation. Inter-cropping, mixed-cropping and sequence cropping of capsicum with solanaceous, cucurbitaceous, cruciferous and leguminous vegetables should be avoided. Cropping sequence with non-host crops like millets has to be practiced in areas where the disease is reported to be widely prevalent.
Bioenrichment:
Application of farm yard manure and neem cake (8% oil content) bioenriched with harzianum Th-2 + B. subtilis BS-2 to planting bed at 600 kg per acre. The addition of compost to the soil resulted in an effective and low-cost disease management solution.
Seed treatment:
Seed treatment & nursery cocopeat enrichment with bioagents harzianum Th-2 + Bacillus subtilis BS-2 @ 10g/kg seed.
Raised bed planting:
Planting on raised bed (90-100 cm wide and 15-22 cm height) with silver-black reflective mulch film (30-100 micron thick).
Soil drainage management:
Provide proper soil drainage to prevent water logging during heavy rains. Soil moisture content strongly influences the development of Phytophthora root rot in capsicum. Plant infection by capsici and root rot development is favored by high soil moisture, while a short period of flooding contributed to a more severe disease.
Soil type selection:
Soil texture has an impact on the development of phytophthora root rot in capsicum. Increased vulnerability to capsici was observed in heavy soils compared to light textured soils under different soil moisture regimes. In areas, where P. capsici is prevalent, cultivation in heavy textured soils has to be avoided.
Sanitation:
Removal of infected low lying diseased or soil touching leaves. Field scouting and removing/ disking infected plants in small areas in the early disease development stages helps to delay the spread of the disease in the fields.
Fungicide application:
Follow sequential fungicide application schedule as detailed below. Give initial protective foliar sprays with chlorothalonil 75% WP and mancozeb 75% WP in rotation at 2g per litre at 15 days interval up to standard meteorological week 40 under Bengaluru weather conditions or until first appearance of leaf lesion at crop growth stage fruit development in other locations.
On notice of first foliar blight lesions, give need based curative sprays and drenching with tank mix of dimethomorph 50% WP (1g/L)+ chlorothalonil 75% WP (2g/L), next rotational spray with tank mix of fungicides, dimethomorph 50% WP (1g/L) + mancozeb 75% WP (2g/L).
Economic analysis of the developed integrated management schedule gave highest gross returns and B: C ratio of 88 in Arka Athulya, 2.52 in Indra, 2.48 in California Wonder and 1.93 in Arka Mohini genotypes of capsicum.
At present there are no capsicum varieties available in India for commercial production with Phytophthora blight resistance. In the absence of resistant varieties, the integrated management schedule developed could be followed to effectively manage this disease in regions of the country where it is prevalent in severe form.
Authors:
Sandeep Kumar G.M., Sriram S and Pavithra R.S.
ICAR-Indian Institute of Horticultural Research,
Hesaraghatta lake post Bengaluru, India-560 089
Corresponding author: sandeepmycologist@gmail.com
