DISEASES OF GINGER

DISEASES OF GINGER

1. RHIZOME ROT
Symptoms:
  • Two types of symptoms i.e. wet and dry rot (Plate 1a and 1b) are generally noticed on rhizomes.
  • The initial symptoms of the disease are noticed on leaves which turn slightly pale.
  • The yellowing of the leaves starts from the tip of the blade and spread downwards. Ultimately the infected leaves are killed which droop and hang down along the pseudostem (Plate 1c).
  • The basal portion of the plant exhibits pale translucent colouration which becomes water soaked and soft.
  • The rotting extends from collar regions to rhizomes.
  • Lesions gradually decompose forming a watery mass of putrifying tissues enclosed by the tough rind of the rhizome (Plate 1d) and the fibrovascular strands are not affected.
  • Roots arising from the affected regions of rhizome also show typical softening and rotting.

15.1

Pathogen (s):
  • The disease is caused by different species of Pythium and Fusarium amongst these important are P. aphanidermatum (Edson) Fitz., P. butleri Subram., P. complectens Braun, P. deliense Meurs., P. gracile (de Bary) Schenk, P. graminicolum Subram., P. myriotylum Drechsler, P. pleroticum T. Ito; Fusarium solani (Mart.) Sacc. and F. equiseti (Corda) Sacc.
  • The hyphae of P. aphanidermatum are hyaline, branched, non septate which form long tapering sporangia by swelling of the hyphae.
  • The sporangium blows out into a vesicle to which the protoplasm migrates.
  • Zoospores are formed in vesicle and are kidney shaped, biflagellate and slightly depressed at the hilum end.
  • The oospores are smooth walled, plerotic and spherical in shape.
  • Fusarium equiseti produces micro and macro conidia.
  • Micro conidia are aseptate whereas macro conidia are 1-3 septate, sickle to spindle shaped.
Disease cycle and epidemiology:
  • The pathogen (s) perpetuate through diseased rhizomes as well as through oospores.
  • The infected plant debris remaining in the field serves as primary source of infection.
  • Oospores have also been detected in the scales of stored rhizomes.
  • A warm and humid climate predisposes the plants to infection at sprouting stage.
  • The spread of the disease is typical of soil borne diseases.
  • For germination of Pythium spp. like P. aphanidermatum and P. myriotylum, the optimum temperature is 34o C and for P. pleroticum is 25-30o C whereas for growth and multiplication of F. equiseti, the optimum temperature is 30o C.
Management:
  • Use disease free seed rhizome for planting and treat by steeping them in the mixture of mancozeb (0.25%) and carbendazim (0.1%) for 60 minutes before storage as well as sowing followed by drying in shade for 48 hours.
  • Follow at least 2-3 years crop rotation.
  • Apply neem cake (250 g/m2) and lime as soil amendment.
  • The antagonistic species of Trichoderma such as T. viride, T. harzianum and T. hamatum are known to inhibit the growth of the pathogenic fungi (40 g/m2).
  • Drench the affected plants with copper oxychloride (0.3%) or Bordeaux mixture (4:4:50) during rainy season.

2. PHYLLOSTICTA LEAF SPOT
Symptoms:
  • On leaves, small oval to elongated spots appear which later on develop white papery centre and dark brown margins with a yellow halo (Plate 2).
  • The affected leaves suffer from extensive desiccation and are shredded and disfigured.

15.2

Pathogen:
  • The disease is caused by Phyllosticta zingiberi T.S. Ramakr.
  • The fungus forms amphigenous, subglobose, dark brown, ostiolate pycnidia on the host. Pycnidiospores are hyaline, unicellular, oblong and biguttulate.
Disease cycle and epidemiology:
  • The fungus overwinters in infected plant debris and seed rhizomes.
  • The disease begins to appear towards the end of June when temperature varies from 23.4 to 29.6 and RH is in between 83.3 to 90.2 per cent.
  • Later, in July when rainy days and total rainfall increases, the disease aggravates and spread fast.
  • Higher intensity of rain, accompanied by wind, exert greater impact on target leaves and fungus is splashed to a greater distance resulting in increased disease incidence.
Management:
  • Collect and destroy the infected plant debris by burning.
  • Use healthy seed rhizomes and by steeping them in the mixture of mancozeb (0.25%) and carbendazim (0.1%) for 60 minutes before sowing and dry in shade for 48 h. Spray the crop with mancozeb (0.25%) or carbendazim (0.1%) or combination of mancozeb (0.25%) and carbendazim (0.05%) and repeat at 10 to 14 days interval.
  • Few cultivars like Narasapatom, Tura, Nadia, Tetraploid and Thingpani are moderately resistant to the pathogen.

B) BACTERIAL DISEASES:

3. BACTERIAL WILT
Symptoms:
  • Water-soaked patches or streaks appear on collar region which slowly enlarge.
  • Bronze colouration on leaf margins is also observed and the leaves slowly become flaccid with intense yellowish bronze colour and ultimately droop down exhibiting typical wilt symptoms (Plate 3a).
  • At advanced stages, pseudo stem appears slimy and if infected rhizomes are pressed, a milky bacterial exudates oozes out in clear water (Plate 3b).

15.3

Pathogen:
  • The disease is caused by bacterium Ralstonia solanacearum (Smith) Yabuuchi et al.
  • The bacterium is described in detail under tomato lecture.
Disease cycle and epidemiology:
  • The bacterium perpetuates through infected rhizomes and soil. Biotype III of the bacterium is known to cause this disease in India.
  • The bacterium has wider host range including both cultivated and weeds.
  • The presence of nematodes has a positive and significant effect on the development of bacterial wilt.
Management:
  • Use healthy seed rhizomes for planting.
  • Eradicate weed hosts and adopt effective crop rotation for at least three years.
  • Treat seed rhizomes with Streptocycline (100 ppm) for 30 minutes before planting and spray the crop with Streptocycline (100 ppm) starting from 1 month after transplanting and repeat at fortnightly interval.

C) NEMATODE DISEASES

4. ROOT-KNOT
Nematodes can attack ginger and turmeric such as root-knot nematode (Meloidogyne incognita).This nematode has a very wide-host range and heavy infections may render drastic reduction of ginger yield.

Symptoms:
  • The symptoms are similar to root gall as on tomatoes, cucurbits, lettuce, and other vegetable crops.
  • Root knot infected ginger may have stunted growth with partial yellowing of plants.
  • On roots irregular round galls and spindle-shaped enlargements appear on the tap and side roots (Plate-4).
  • The nematode larvae feed on roots causing the swellings or knots that are characteristic of root-knot infection.
  • Roots are often stunted and deformed

15.4

Pathogen:
  • Root-knot nematode is caused by the plant parasitic nematode, Meloidogyne incognita.
  • Root knot nematodes are sedentary, endoparasitic and gall producing nematodes.
  • The infective stage is the second stage juveniles, which have lightly sclerotized cephalic framework.
  • The stylet in juveniles and adult female is weak.
  • Third and fourth stage juveniles lack stylet and body is saccate.
  • Adult females are swollen, pyriform, saccate with short neck, vulva is terminal, perineal cuticular pattern of striae is present, tail is absent, didelphic, prodelphic ovaries are coiled, excretory pore is present near stylet base, large rectal glands produce gelatinous matrix expelled through the anus.
  • Males are vermiform with single or paired testis, tail end is twisted and rounded, bursa is absent, reproduction is parthogenic.
Disease cycle and epidemiology:
  • The second stage juveniles in the soil after searching a suitable site, normally behind the root cap, start feeding on epidermal cells and penetrate in cortical layers of root.
  • They reach upto the stellar region, where they form giant cells for feeding.
  • Second stage juveniles initiate gall formation and feed for 7-15 days, undergo three moults to become adult.
  • The total time taken for completing one life cycle under optimum conditions is 3-4 weeks.
  • Moderate temperature (29-30oC) and higher relative humidity (79-80%) favour M. incognita reproduction and spread.
Management:
  • Crop rotation with non-hosts, graminaceous poor hosts and a few antagonistic crops for one or two years have been reported to be effective in reducing the population of root knot nematode.
  • Groundnut-mustard rotation was found most effective in reducing the population of M. incognita.
  • Soil amendments (dry or green crop residues, oil cakes, meals, sawdust, FYM etc.) are allowed to decompose in the nematode infested field, which in turn helps in alteration of physical, chemical and biotic conditions of the soil.
  • At the time of field preparation, nematicides like Thimet or Phorate (12-15 kg/ha) should be applied and immediately apply light irrigation. After 15-20 days again cultivate the field and sow the crop.
  • Efficacy of various biocontrol agents like Paecilomyces lilacinus, Pasteuria penetrans and Pseudomonas fluorescens in managing M. incognita has also been reported.
Other diseases of importance:
i. Yellows : Fusarium oxysporum Schlechtend f.sp. zingiberi Treujillo
ii. Chlorotic fleck : Ginger Chlorotic Fleck virus
iii. Big bud : Tomato Big Bud Phytoplasma
Last modified: Friday, 2 March 2012, 5:23 AM