The garlic (
Allium sativum L.) is useful to mitigate the effect of medicinal and culinary properties throughout the world. Biochemical constituents including thiosulfinates, thiosulfonates, allicin, ajonen that make the crop very precious in human health care system. Effective antimicrobial properties of garlic have been well accepted. The crop has exhibited a potential therapeutic medicinal value with antifungal, antibacterial, antiviral, anti helmantic, antiseptic and anti-inflammatory properties. The most recent classification scheme of garlic is class Liliopsida, subclass Liliidae, superorder Liliianae, order Amaryllidales, family Amaryllidaceae subfamily Allioideae, tribe Allieae and genus Allium which is mainly based on the sequences of nuclear ribosomal DNA
(Reuter et al., 1996).
Garlic is a herbaceous annual bulbous plant in the family Amaryllidaceae grown for its pungent, edible bulb. The garlic plant can either have a short, woody central stem (Hard neck) or a softer pseudo-stem made of overlapping leaf sheaths (soft neck). India ranks second with 2.0 lakh ha area and production with 10.58 lakh tons at global level, However, productivity remains low with 5.05 t/ha as compared with Egypt (25.28 t/ha) and China (23.60 t/ha). Long day and Short day type of garlic are cultivated in India. In Madhya Pradesh short day type varieties are grown. Long day type of garlic is confined to hills of India, especially in Jammu and Kashmir, Himachal Pardesh and Uttrakhand region. Worldwide, garlic was grown over 14.22 lakh hectares and had a total production of 237.70 lakh tons and an average productivity of 16.71 t/ha (Source: FAOSTAT, 2013). Among 140 countries where garlic is grown, China is world leader in production (80.92%), followed by India (4.45%). Per hectare productivity of garlic is the highest in Egypt (24.36 t/ha).
The garlic crop is cultivated in several countries and susceptible to number of diseases at various stages of plant growth (
Walker, 1952). From different parts of the world, downy mildew, rust, purple blotch; Stemphylium blight, basal rot, have been observed leading to substantial losses (
Ahmad and Karimullah, 1998;
Apaza and Matos, 2000;
Schwartz and Mohan, 1995;
Evarts and Lacy, 1990).
Investigation on various aspects of Purple blotch (
Alternaria porri)
(Dhiman et al., 1986; Quadri et al., 1982); Stemphylium blight
(Thind et al., 1985; Singh et al., 1977), basal rot (
Fusarium oxysporum) (
Mathur and Sankhala, 1963) Rust (
Puccinia porri) (
Sandhu and Kang, 1988); garlic mosaic virus (
Ahlawat, 1974), downy mildew
(Singh et al., 1987) are reported from India. Management approaches for purple blotch; Stemphylium blight, basal rot, rusts; garlic mosaic virus, downy mildew has been worked out in various agro ecological zones of India
(Shrivastava et al., 1992; Anonymous, 2013).
Various diseases have been reported on garlic bulbs in particular are affected by association of number of fungal pathogens both in fields and storages. The bulbs due to handling, cultivation practices and ill storage are infected severely by number of fungal pathogens. The bulbs are significantly damaged and destroyed resulting in bulb rot and bulb necrosis (
Rai and Agarwal, 1976; Georgieva and Kotev 1977).
In India
Garlic was grown on Madhya Pradesh, Gujarat, Rajasthan, Uttar Pradesh, Assam, Punjab, Maharashtra on various aspects of Purple blotch (
Alternaria porri)
(Dhiman et al., 1986; Quadri et al., 1982); Stemphylium blight
(Thind et al., 1985; Singh et al.,1977), basal rot (
Fusarium oxysporum) (Mathur and Sankhala, 1963) Rust (
Puccinia porri) (
Sandhu and Kang, 1988); garlic mosaic virus (
Ahlawat, 1974), downy mildew
(Singh et al., 1987) are reported from India. Management approaches for purple blotch, Stemphylium blight, basal rot, rusts, garlic mosaic virus, downy mildew has been worked out in various agro ecological zones of India
(Shrivastava et al., 1992).
Prevalence and management of garlic diseases
White rot (Sclerotium cepivorum)
Distribution
The disease has been recorded from various part of India and abroad. White rot is one of the most important garlic diseases in the world, including Iran.
Sclerotium cepivorum Berk. The causal agent of white rot and is found in practically all regions where species of Allium are grown (
Entwistle, 1990;
Crowe et al., 1993; Schwartz and Mohan, 1995; Davis et al., 2007).
Management
Allempts have also made to evolve and approchesas IPM technique using sclerotial germination stimulants in a field prior to planting there after introducing a biological control agent at the time of sowing. A number of research groups are investigating multiple approaches to disease control,that include combining solarization, biocontrol and application of vermicompost germination stimulants, fungicides and solarization (
Dennis, 1997;
Metcalf and Wilson, 1997). Application of microbial antagonists has shown a suitable ecologically-friendly candidate which could replace chemical pesticides. Different fungal and bacterial antagonists have proved to be potential bio control agents for controlling many plant pathogenic fungi (
Cook and Baker, 1988). Different species of
Trichoderma have been successfully used and have produced promising results for controlling garlic seedling basal rot disease
(Metcalf et al., 2004; Heydari and Pessarakli, 2010;
Sharifi et al., 2010; Francisco et al., 2011; Kakvan et al., 2013; Naraghi et al., 2013; Blaszczyk et al., 2014; Khiyami et al., 2014).
Naeimi and Zare (2014) have conducted studies using chemical and bioagent the study was conducted during 2013/14 under greenhouse condition. The results of the study revealed that the efficacy of both fungicides, when tested alone, against
S. cepivorum was lower than those treated with
Trichoderma spp. alone and the fungicide combined treatments. Among all treatments, (Apron Star 42 WS fungicide combined with
T. hamatum and
T.
viride) has provided the best antagonistic activity against
S. cepivorum with no disease incidence, followed by
T. viride alone and Tebuconazole combined with
T. hamtum both 11.1% incidence.
Gupta et al., (2011), Ahmad and Tribe (1977) have noticed that biocontrol agents
T. viride, Gliocladium zeae and
Coniothyrium minitans provided effective control of white rot disease of garlic.
Trichoderma as a potent fungal biocontrol agent against a range of plant pathogen has attracted considerable scientific attention.
Chaube et al., (2002) and
Harman et al., (2004) concluded that bio agent produce volatile and non volatile antibiotic compounds, which inhibit fungal growth at very low concentration and
Trichoderma species are among the most promising bio control agents against many fungal pathogens (
Rini and Sulochana, 2007;
Akrami et al., 2009).
Fungal and bacterial antagonists have been proved to be potential biocontrol agents for controlling many plant pathogenic fungi
(Metcalf et al., 2004; Heydari and Pessarakli, 2010;
Sharifi et al., 2010; Francisco et al., 2011; Kakvan et al., 2013; Naraghi et al., 2013; Blaszczyk et al., 2014; Khiyami et al., 2014).
White rot disease caused by
S. cepivorum could be controlled by application of bio agent
Trichoderma were used in study, because the antagonistic fungus has effectively been used in the control and management of different plant diseases in the previous studies
(Francisco et al., 2011; El-Hassan et al., 2013; Kakvan et al., 2013; Naeimi and Zare, 2014).
Purple blotch (Alternaria porri)
Distribution
The disease has been observed in all the major onion and garlic producing regions. Purple blotch caused by
Alternaria porri has been reported in India and abroad
(Hausbeck et al., 1999; Meyer et al., 2000). In Pakistan, fungal diseases cause a lot of problems in the production of onion and garlic. In fungal diseases, purple blotch of onion that is caused by
Alternaria porri is a major threat for the onion and garlic crop
(Lancaster et al., 1996). In India, the diseases caused by unseasonal rains have ruined almost 70 per cent of the
kharif garlic crop in Maharashtra in 2010, which is responsible for the nationwide shortage of the commodity (
Shrivastava, 2010).
Management
Use of disease free bulb should be selected for planting. Seeds should be treated with Thiram @ 4 g/kg seed. The field should be well drained. Three foliar sprayings with Copper oxychloride 0.25% or Chlorothalonil 0.2% or Zineb 0.2% or Mancozeb 0.2% were effective (Anonymous, 2011).
Bisht and Thomas (1992) have evaluated several systemic fungicide for the management of the disease. Purple blotch caused by
Alternaria porri is a major constraint and causesd severe yield loss. Borkar and Patil (1995) reported that purple blotch and stemphylium blight disease of garlic could be managed by 3 to 4 sprays of 0.25% mancozeb at 10 days intervals that reduced the incidence and intensity of foliar diseases of garlic under condition of Maharastra.
Studies conducted on management of purple blotch in Marathwada region of Maharashtraand revealed that lowest disease severity of purple blotch with spray of mancozeb @ 0.25%, hexaconazole @ 0.1% and difenconazole @ 0.05%. systemic fungicides tebuconazole @ 0.1% and azoxystrobin @ 0.1% have effectively controlled purple blotch disease of garlic.The highest percent efficacy of disease control (PEDC) of purple blotch (62.21%) with foliar sprays of mancozeb @ 0.25% followed by tebuconazole @ 0.1% (55.63%) andazoxystrobin @ 0.1% (54.78%) in comparison was noticed
(Wangikar et al., 2012).
Tripathy et al., (2014) reported that purple blotch disease in garlic. Could effectively managed by mancozeb @ 0.25%+methomyl @ 0.8 g per lit. tricyclazole / propiconazol @ 0.01%+carbosulfan @ 2 ml per lit. and copper oxychloride @ 0.25% / hexaconazole @ 0.1%+profenofos 1 ml per lit. At 30, 45 and 60 DAT against purple blotch under Odisha condition efficacy of tricyclozoles, propiconazole and hexaconazole in controlling
Alternaria porri has been reported.
Maximum disease incidence in field was recorded on plants sprayed with Dora (54.05%) followed by Dorazole (43.31%), Score (36.54%) but the lowest disease incidence was on plants that were treated with Mancozeb (22.22%) as compared to control with 78%. Dithiocarbamate, which is active ingredient of Mancozeb, destroys fungal spores (
Koike and Heinderson, 1998).
Pandey et al., (2002) tested fungicides against purple blotch which is a common disease of onion and garlic and reported that all fungicides significantly controlled disease but Indofil M-45 (Mancozeb) was found the best in respect to disease control.
In vitro screening of fungicides revealed to be highly fungitoxic Mancozeb was the effective fungicide against purple blotch and four sprays of Mancozeb @ 0.3% with Monocrotophos @ 0.05% was the best treatment and recorded the least disease incidence and highest yield (
Vijay and Rahman, 2004).
Efficacy of bioagents against the disease has been reported. Among the bio agents,
T. harzianum @ (1%) was found to be effective in delaying diseases severity with optimum yield (1134.44 kg/ha) over check (893.33 kg/ ha) (Vannaci and Harman, 1987; Sharma, 2012;
Shahnaz et al., 2013).
Aujla et al., (2010) noticed that application of Tebuconazole and Propiconazole were the most effective fungicides against purple blotch disease of onion and garlic and resulted in lowest disease severity (6.1 and 7.3 per cent respectively) with 73.0 and 66.6 per cent increase in seed yield over untreated control under Punjab conditions.
Basal rot (Fusarium oxysporum)
Distribution
The basal rot disease has been reported around the world, including India, Thailand, China, Japan, Iran, Israel, Australia and Europe (FAO, 1999). Species of Fusarium including
F. oxysporum, F. culmorum and
F. proliferatum occur in North America.
In India, the incidence of basal rot was first reported in Coimbatore, Tamil Nadu (
Mathur and Shukla, 1963;
Ramakrishnan and Eswaramoorthy, 1982).
Management
Trichoderma spp.and
Pseudomonas sp. were screened against
F. oxysporum f. sp.
cepae by the dual culture method (
Riker and Riker, 1936;
Dennis and Webster, 1971).
Biological controls using fungal and bacterial antagonists have been suggested as a possible control method. Under
in vitro conditions, fungal antagonists,
Trichoderma viride, T. harzianum, T. hamatum, T. koningii and
T. pseudokoningii and bacterial antagonists,
Pseudomonas fluorescens and
Bacillus subtilis were effective (
Rajendran and Ranganathan,1996).
Stemphylium leaf blight (Stemphylium vesicarium)
Distribution
The Stemphylium blight has been reported throughout the regions wherever the garlic is produced. It has now been observed in many countries worldwide, including the USA, South Africa, Spain, Brazil, Australia, Egypt and China (
Rao and Pavgi, 1975,
Miller et al., 1978; Zheng et al., 2008).
During the past 20 years the disease has become increasingly important in temperate and tropical regions throughout the world. It is a major disease of garlic in Southeast Asia and India. Stemphylium blight (
Stemphylium vesicarium) is also an important foliage disease of garlic crop prevalent in almost all the onion cultivated areas of Northern and Eastern India
(Gupta et al., 1996; Suhag and Bhatia, 2006).
Management
Gupta et al., (1996) reported that
Stemphylium vesicarium is one of the major destructive diseases of garlic crop grown in the state of Maharashtra. Bio-efficacy of eight fungicides was evaluated
in vitro against
Stemphylium vesicarium. All the fungicides tested were found/fungicidal against the pathogen and significantly inhibited mycelial growth of the pathogen over untreated control. However, Mancozeb 75 WP recorded significantly highest mean inhibition (90.01%) followed by Carbendazim 50 WP and Copper oxychloride 50 WP which recorded mean growth inhibition, respectively of 89.25 and 86.86 per cent. Chlorothalonil 75 WP (84.77% inhibition), Difenconazole 25 EC (84.02% inhibition), Thiophanate methyl 70 WP (78.21% inhibition), Penconazole 10 EC (77.61% inhibition) and Hexaconazole 5 EC (76.43% inhibition) were promising for effective management of Stemphylium leaf blight of garlic
(Srivastava et al., 1995).
The fungicide mancozeb and Copper oxychloride have been reported most effective and economical fungicides against stemphylium blight and purple blotch disease
in vitro as well as under field conditions
(Jakhar et al., 1996). Among the new fungicides tested Tebuconazole, Propiconazole and the combination of Carbendazim 12% + Mancozeb 63% WP have proved highly effective fungicides against the disease and the fungicides can further be used as an alternate fungicide in place of conventional fungicides
(Hug et al., 1994).
Studies revealed that Tebuconazole 25.9 EC, Propiconazole 25 EC and the combination of Carbendazim 12% Mancozeb 63% (SAAF) appears to be promising alternatives to the conventional fungicides Mancozeb 75 WP and Copper oxychloride 50 WP for efficient management of stemphylium blight disease of garlic crop. Among the diseases, foliar blight plays an important role in decreasing the yields. A number of pathogens have been found responsible for the disease, of which
Alternaria porri,
A. alternata and
Stemphylium vesicarium are the most common
(Gupta et al., 1996). They reported that Mancozeb was at par with Hexaconazole (at 0.06%) in which disease intensity of 32.35 and 13.59 per cent was recorded during first and second year, respectively. The efficacy of Mancozeb in the control of foliar blight of garlic
(Srivastava et al., 1996) has been established.
Srivastava and Tiwari (2003) reported the efficacy of bio-control agents as compared to fungicides might be due to adverse environmental conditions causing their rapid desiccation.
T. viride was found to increase germination of garlic clove.
The severity of Stemphylium blight was indexed at 30, 45, 60 and 75 days after transplanting on a 0-5 scale and per cent disease index (PDI) was computed (Sharma, 1995).
Identification of diseases at field level
White rot
The initial symptoms of white rot disease were the yellowing of leaves and later roots were destroyed. The leaves of infected plant exhibited girdling and dieback. Leaf decay at the base was observed and older leaves collapsed first. A semi watery decay of the stalks of bulb was recorded. The infected plant was easily pulled out from ground. Root was rotted. White fluffy growth around the base of the bulb was observed. The white fluffy fungal growth became more compact as the disease progressed, at later stage numerous small spherical black bodies (Sclerotia) formed on the mycelial mat, the sclerotia were approximately of the size of pin head, poppy seed, resembling mustard grain, the bulbs became soft and water soaked. Based upon the fungal mycelium and sclerotium the fungus was identified as
Sclerotium ceviporum.
Pink rot
The garlic affected by basal rot pathogen exhibited progressive yellowing. Affected roots were brown to dark pink. In severe condition of infection white fungal growth was noticed at the base infected bulb, when the infected bulb cut vertically a brown discoloration on the spilt was apparent. In some cases stem plate tissue became pitted and showed dry rot. Under dry conditions the stem plate lead to crick scales. In advanced stage the bulb started decaing from lower and ultimately whole plant died. On the basis of fungal characteristics the pathogen was identified as
Fusarium oxsysporum.
Purple blotch
The purple blotch symptoms were noticed on stalks as small sunken whitish flacks, with purple coloure. Later the lesion girdled leaves and stalks leading the drooping. Oval shaped tan and deep purple lesions on leaves margin were recorded. Concentric zone were observed within the lesions. The initial symptoms of purple blotch were small water soaked lesion that appeared on older leaves. As the disease progressed the lesion on larged became yellow and concentric ring formed on margins. Based on the fungal characteristics the pathogen was identified as
Alternaria porri.
Stemphylium tender tip blight
The symptoms appeared as small yellow to orange flacks which turned brown, extended along the blade in both direction from the lesions. In advanced stages lesions girdled and killed leaves and stem, due to infection of
Stemphylium vesicarium, under field conditions. Purple blotch and Stemphylium disease were differentiated on basis of margins of the lesions. In Stemphylium lesions were elongated spherical shaped surrounded in pinkish margin while in purple blotch small sunken whitish flacks with purple colour centres and the lesions were surrounded by yellow hallow.
