भारत में मक्का फसल के 8 प्रमुख रोग
In India, the area of land given to maize ranks fifth after rice, wheat, sorghum and pearl millet. In grain production maize holds fourth position over pearl millet. The 61 diseases of maize recorded so far are considered to constitute the major constraints, limiting production.
The major diseases are: four foliar diseases, two pre-flowering and three post-flowering stalk rots, four downy mildews and two sheath diseases. Information on ear, cob and kernel rots, and smut and virus diseases is presented. Four major approaches of disease management in the Indian context are outlined and the most appropriate one is considered to be host resistance.
Adoption of this approach has yielded promising results for five major disease groups. It is pointed out that, so far, among the materials released which are resistant to one disease, or one set of diseases, most turn out to be susceptible to another set of diseases.
The development of multiple resistance to the major diseases prevalent in the diverse agro-ecosystems of India seems more appropriate. The population improvement approach through a recurrent selection scheme was adopted and since 1973, a high level of resistance to as many as 12 diseases has been developed.
Although seven disease groups are amenable to chemical control, a very favorable cost: benefit ratio (1: 14) is obtained only for seed and seedling groups of disease. Certain agronomic practices also help in reducing incidence of certain disease groups. The total estimate of loss in economic product per annum due to all diseases taken together has been estimated to be 13.2%.
Some major epidemics
Six major disease outbreaks have been recorded in India since the 1960s. Bacterial stalk rot (Erwinia chrysanthemi p.v. zeae) appeared in the Tarai area of Uttar Pradesh in 1959 and in 1969 in Himachal Pradesh on Hybrid Ganga 5. Brown stripe downy mildew (Sclerophthora rayssiae var. zeae) appeared in 1962 and 1964 in West Bengal hills, 1964 in Western Madhya Pradesh and South Eastern Gujarat, 1964 in North Bihar and in 1965 in the Tarai region of Uttar Pradesh and parts of Himachal Pradesh.
There was an outbreak of sorghum downy mildew Perenosclerospora sorghi in Rajasthan, Karnataka and Tamil Nadu from 1968 to 1973. Common rust appeared from 1973 onwards in the rabi season on hybrids Ganga Safed 2 and Hi-starch in Bihar.
Virulent strains of Exserohilum turcicum appeared in 1974 or hybrid Ganga 5, Deccan, Pio X104, X114 and Kisan. In the late 1960s there was an outbreak of banded leaf and sheath blight pathogen in Himachal Pradesh and other areas of Western Himalayas (Sharma and Payak, 1981).
1. Stalk Rots of Maize
Stalk rots are caused by several fungi and bacteria which affects the plants near maturity. Losses from stalk rot vary region to region and are estimated 10 – 20 %. Losses are caused either by poor filling of the cobs or due to lodging of affected plants. The following pathogens are associated with stalk rot of maize.
Bacterial Pathogens:
- Pseudomonas avenae sub-sp. avenae
- Enterobacter dissolvens (Rosen) Brenner et al. = Erwinia dissolvens (Rosen) Burkholder.
- Erwinia carotovora sub-sp. carotovora (Jones) Bergey et al. = chrysanthemi pv. Zae (Sabet) Victoria et al.
Fungal Pathogens:
- Colletotrichum graminicola (Ces.) G.W. Wils., Telemorph: Glomerella graminicola (Politis), tucumenensis (Speg.) Arx & E. Muller.
- Physoderma maydis (Miyabe) Miyabe
- Diplodia maydis (Berk.) Sacc.
- Fusarium moniliforme Sheld var. subglutinans Wollenweb & Reinking
- Gibbrella zeae (Schwein) Petch. (Anamorph: Fusarium graminearum
- Setophaeria turcica (Luttrell) K.J. Leonard & E.G.Suggs (Anamorph: Exserohilum turcicum (Pass.) K.J. Leonard & E.G. Suggs = Helminthosporium turcicum
- Pythium aphanidermatum (Edson) Fitzp.
- Rhizoctonia solani = R. zeae Voorhees = R. solani sub sp. sasakii
- Cochliobolus heterostrophus (Drechs.) Drechs. Anamorph: Bipolaris maydis (Nisikado & Miyake) = Helminthosporium maydis (Nisikado & Miyake).
- Fusaium spp., Mucor sp., Spicaria spp. & Rhopographus zeae
Symptoms: Stalk rot and ear rot are the two important phases of the disease. In stalk rot, symptoms appear after a few weeks of pollination as premature dying of lower leaves which turn into dull grey appearance. The internodes become soft and appear tan to brown from outside and pink or reddish inside. The pith is completely rotten and the stalk may lodge. Plants may die if harvesting is delayed. In ear rot, ears may not completely and a pinkish mold can be seen between ear and husks.
Pathogens: Gibberella zeae; Diplodia zeae; Fusarium species and Colletotrichum graminicola are the major pathogens involved in the rot complex but G. zeae dominates in the complex. The fungus produces ascospores in perithecia, mycelium, or chlamydospores in infected plant debris. G. zeae also produces mycotoxins which are toxic to human and animals.
Disease Cycle: The pathogens survive in soil from one growing season to another. The spores are blown off by wind into the base of leaf sheath and cause infection either by directly penetrating into the host or through wounds caused by insects such as stem borer. Conidia are produced on infected plant parts and serve as secondary inoculum. The disease is favoured by wet weather near or after silking. Higher plant density, high nitrogen and low potash doses and early maturity of hybrids also favour the disease.
Control: The preventive measures for disease management are use of resistant varieties, low plant density, proper fertility practices, insect control and timely harvesting.
2. Downy Mildews of Maize
Downey mildews are found worldwide but they cause serious diseases in Asia and Africa on maize and other grain crops. These diseases cause considerable losses to the yield under favourable conditions of fungal growth. These diseases cause severe damage to hybrid maize like Ganga-3 etc. Several mildews are known as mentioned below:
- Brown stripe mildew caused by Sclephthora rayssiae Kenneth et al. var. zeae Payak & Renfro.
- Crazi top downy mildew caused by Sclephthora macrospora (Sacc.) Thirumalachar et al. =Sclerospora macrospora Sacc.
- Green ear downy mildew caused by Sclerospora graminicola (Sacc) J. Schrot.
- Philippine downy mildew caused by Peronosclerospora philippinensis (W.Weston) C.G.Shaw
- Spontaneum downy mildew caused by Peronosclerospora spontanea (W.Weston) C.G. Shaw. = Sclerospora spontanea Weston.
- Sorghum downy mildew caused by Peronospora sorghi (Weston & Uppal) C.G.Shaw = Sclerospora sorghi Weston and Uppal.
- Sugarcane downy mildew caused by Peronosclerospora sacchari (Miyake0 Shirai & Hara = Sclerospora sacchari Miyake
Symptoms: The symptoms appear on younger leaves as white or light green stripes which soon become white or light yellow on most of the leaves of affected plants. The sporangia develop on branched sporangiophores which emerge in groups from the plant tissues through stomata.
A white mat of the fungal growth can be seen on the lower or both the surfaces of leaves during wet weather. The stem may also be affected if infection occurs during early stages of plant growth.
Pathogens: Sclerophthora rayssiae, Peronosclerospora maydis; P. philippinensis; P. sorghi and P. sacchari are commonly distributed downy mildew pathogens. These pathogens belong to the group Oomycetes and family peronosporaceae. The first two pathogen attacks maize but the rest two are the pathogens of sorghum and sugarcane respectively but also infect maize.
The S. rayssiae produces sporangia at the tips of sporangiophores at their branches. Sporangia are white in colour in the beginning but turn to greyish light brown later. The sporangia germinate by protruding a germ tube and finally produce zoospores at higher temperature. The P. philippinensis fungus produces numerous hyaline, thin walled, ellipsoidal conidia on dichotomously branched conidiophores.
Disease Cycle: Downey mildews are soil and seed borne in nature. The spores in the soil or on seeds germinate through a germ tube and infect plant tissues through roots or collar region. This is called as primary infection.
The infection becomes systemic and reaches at the upper parts of the plants. The fungus develops sporangia in large numbers on the younger leaves of affected plants. The sporangia blown away by wind or through rain water or insects and infect healthy plants. This is the secondary spread of the disease where they form zoospores which cause the secondary infection.
Control: The control of mildew diseases is difficult. The sprays with systemic fungicides such as metalaxyl and propamocarb etc. can be used to manage the disease. However, the best control is to use resistant varieties or hybrids, if available.
3. Leaf Spots of Maize
Leaf spots of maize are caused by several bacteria and fungi and they develop their respective symptoms on leaves of maize plants. Leaf spots of various sizes are caused by different pathogens. The following bacteria cause leaf spot symptoms on maize plants.
Bacterial leaf spot caused by Xanthomonas campestris pv. Holicola (Elliott) Dye; Chocolate spot caused by Pseudomonas syringae pv. Coronafaciens (Elliott) Young et al.; and holcus spot caused by P. syringae pv. Syringae Van Hall.
The following fungi causing spots or lesions on leaves are:
- Brown spot caused by Physoderma maydis (Miyabe) Miyabe;
- Curvularia leafspot caused by Curvularia species such as clavata P.C. Jain; = C. maculens (Bancroft) Boedijn (telemorph: Cochliobolus eragrastidis (Tsuda & Ueyama) Sivanesan; C. lunata (Wakk) Boedijn (telemorph: (Cochliobolus lunatus R.R. Nelson & Haasis); C. pellescens Boedijn (Teliomorph: Cochliobolus pellescens (Tsuda & Uema) Sivanesan );
- Gray leafspot caused by zeae-maydis Tehon & E.Y. Daniels;
- Didymella leaf spot caused by Dodymella exitalis (Morini) E. Muller;
- Phaeosphaeria leafspot caused by Phaeosphaeria maydis (P.henn) Rane, Payak & Renfro = Sphaerulina maydis Henn.
- Zonate leafspot caused by Gloeocercospora sorghi Bain & Edgerton ex Deighton. Leaf spots are also caused by several species of Alternaria such as Alternaria alternata and tritici. Zonate leafspot, grey leaf spot and brown leaf spot are important.
4. Zonate Leaf Spot
The disease symptom appears as oval and black brown lesions near the leaf veins. These spots enlarge and may coalesce and cover the leaf surface. Affected leaves may die and fall down. The pathogen, Gloeospora sorghi develop slimy masses of conidia on the surface of lesions which are dispersed by wind or rain. High temperature and humidity favour the disease development more rapidly.
When the lesions are old, small sclerotia are formed in the infected tissues and survive over season in infected tissues or contaminated seeds and become the primary source of inoculum when the crop is sown. The disease can be managed by using certified seed, crop rotation and the use of fungicides like benomyl, Bordeaux mixture, maneb etc.
5. Grey Leaf Spot
The disease is caused by Cercospora zeae-maydis. The leaf spots are brown, narrow and long which become ash grey in humid weather. The lesions may coalesce covering the whole surface of the leaf. During severe attack the affected leaves may fall down.
The fungus produces long, slender, colourless to dark, curved multicellular conidia on conidiophores. The conidia developed on tips of conidiophore and can be easily blown off by wind and cause infection to healthy plants. Most cercospora species produce mycotoxin, cercosporin which kills cells in light. The pathogen overwinters on or inside seed and also on affected leaf tissues as mycelium or spores.
The disease is retarted by dry weather. Most of the Cercospora species have teleomorph as cochliobolus but teleomorph of grey leafspot fungus is not known. The control strategies are applicable as with zonate leaf spot.
The brown water soaked lesions appear on leaves. The spots may coalesce and form larger, brown patches. The lesions are mostly found on basal portion of leaves but may also appear on leaf sheaths and stem. The causal fungus, Physoderma maydis belongs to family Physodermaceae, order Chytridiales of the sub-division Chytridiomycota. The sporangia are brown in colour and are air born and release zoospores. Zoospores attach to leaf and cause infection. The fungus is an obligate parasite. Field sanitation can control the disease.
6. Helminthosporium Leaf Spots
These leafspots are caused by five species of Helminthosporium; H. turcicum; H. maydis; H. carbonum; H. rostratum and H. sativum and all these species are found in India. The first three species cause severe diseases. The genus Helminthosporium was converted to Drechslera and finally has been placed to genus Bipolaris. These diseases are also called as leaf blights and Northern leaf blight in America.
7. Maydis Leaf Spot
The disease is caused by Drechslera (= Bipolaris) maydis (Nisik) Subram. & Jain) and the perfect stage or teliomorph is Cochliobolus heterostrophus (Drechsler) Drechsler. The symptoms appear as large number of minute to large spots of 3.75 cm long and 1.75 cm in width on leaves .
The lesions are oval and zonated. These lesions coalesce and leaves may show brown coloured stripes. The growth of affected plants is stopped and devoid of cob formation. The infection takes place by the inoculum which survives as mycelium or conidia on leaf debris in soil.
The conidia develop on conidiophores under favorable conditions of temperature over 35 C and high humidity. The control measures as applicable with turcica leafspots are also applicable with maydis leaf spot disease. The resistant hybrid such as Ganga white-2 and composite maize like Vijay etc. have been developed in India.
8. Turcica Leaf Spot or Leaf Blight
The disease symptoms appear as boat shaped, light grey or brown lesions on lower leaves and also on the upper leaves. In severe infections, all the leaves are affected and infected plants look like cold injury. The cobs are small and poorly filled. The disease predisposes the plants for bacterial stolk rot. The perfect stage of the pathogen Bipolaris turcicum is Trichometasphaeria turcica (Pass.) Luttrell.
The fungus develops conidia on the conidiophores which are geniculated and each conidium has 3 – 8 septa and is slightly curved. The conidia reach to the host through wind and cause infection through bipolar germination on free water on leaf and at a temperatue from 18 -27 C. They can cause leafspot symptoms within 7 – 12 days. The perfect stage, T. turcica forms the perithecia in which Asci and ascospores are enclosed. The control measures are use of certified disease free seeds, crop rotation and use of resistant cultivars.
References:
- Payak, M, M, and Sharma, R. C.1985. Maize diseases and approaches to their management in India, Tropical Pest Management, 31:4, 302-310
- The CIMMYT Maize Program. 2004. Maize Diseases: A Guide for Field Identification. 4th edition. Mexico, D.F.: CIMMYT.
- Peter J. Balint-Kurti., and Gurmukh S. Johal. 2009. Maize Disease Resistance. Springer Science + Business Media. Handbook of Maize: It’s Biology,
Authors
Parthasarathy. S., Ramalingam. K and Sivakumar. S. S
Department of Plant Pathology,
Centre for Plant Protection Studies (CPPS),
Tamil Nadu Agricultural University, Coimbatore – 641 003
Email;