DISEASES

DISEASES

1. PHYTOPHTHORA FOOT ROT:
The disease was first reported in 1902 from Wynad district of Kerala. The crop losses due to foot rot of black pepper have been reported to the tune of 119 to 905 tonnes per annum in Kerala.

Symptoms:
  • The symptoms start as water soaked lesions on the lower surface of the leaves (Plate 1a) and these lesions later enlarge rapidly, involving 25-70 per cent of the leaf lamina (Plate 1b).
  • With the onset of south-west monsoon during may –June, runner shoots arising from the base of the vine are also infected.
  • The leaves later become flaccid and droop and the plants show die-back symptoms.
  • The foot rot infection occurs as wet patch at the collar region of the vine resulting in varying degree of rotting of the main stem (Plate 1c).
  • There is yellowing and gradual drying of the foliage leading to sudden death of the plant and hence the disease is also called quick wilt (Plate 1d).

20.1

Pathogen:
  • The disease is caused by Phytophthora palmivora (Butler) Butler but now it is changed to P. capsici Leonian.
  • Mycelium is hyaline, branched 3.3-8.6 µm wide and non-septate but few septa are found in case of old hyphae, typically hyphal branches arise at right angles, often variously swollen and tuberous and of abnormal diameter.
  • Sporangia are rarely produced or almost absent in culture, the sporangia are hyaline, ovoid to pyriform or sometimes round to lemon shaped, non-pedicillate with a predominant, hemispherical papilla at the apex.
  • The zoospores are reniform to oval, biflagellate and remain motile for 20-30 minutes, then shed flagella and become encysted and germinate by means of germ tubes.
  • Oospores are formed abundantly in aerial as well as submerged mycelia in the medium.
  • The oogonia are hyaline, circular to spherical, the oogonial stalk is encompassed by persistant amphygynous antheridium.
  • The oospores are circular to spherical, the oospores are found to germinate either by germ tubes or by the rupture of oosporic walls.
  • The fungus does not produce chlamydospores.
Disease cycle and epidemiology:
  • The pathogen is soil borne and infected plant debris serves as the major source of inoculum.
  • A temperature of 23-29o C, relative humidity of 81-99 per cent, daily rainfall of 15.8-23 mm and sunshine of 3.5 h /day favours aerial spread.
  • Vertical and lateral spread of the disease is noticed due to rain splashes during foliar infection.
  • The disease gradually spreads to the upper region of the bush with intermittent rain splashes.
Management:

i) Use healthy planting material.
ii) Removal of infected vines from the plantation is essential to reduce the inoculum buildup. The movement of soil through farm implements from diseased to healthy gardens may also be prevented.
iii) Application of soil amendments like neem cake, cotton seed and groundnut meal (250 g/m2) is also useful in managing the disease.
iv) Two sprays of Bordeaux mixture (5:5:50) during the pre monsoon and mid monsoon period reduce the aerial infection.
v) To minimize the soil borne inoculum, drenching of soil around the vines with copper oxychloride (0.3%). Fungicides like metalaxyl + mancozeb (0.25%) or cymoxanil + mancozeb (0.25%) can also be used for spraying.
vi) Soil application of bioagents like Trichoderma virens and T. harzianum @ 5x 105 cfu/g inoculum has also been found effective in the management of this disease.
vii) Different species of pepper like Piper colubrinum, P. arboretum and P. sarmentosum have been found resistant while cvs. like Narayakodi, Kallu valley, Uthirankotta and Balankotta were tolerant to this disease.

2. SLOW DECLINE OR WILT
Symptoms
  • It is considered to be a complex disease caused by a combination of fungi and nematodes coupled with soil moisture stress and malnutrition.
  • Meloidogyne incognita in combination with Fusarium solani Sacc. f. sp. piperi results in the wilt (Plate-2).
  • The pathogenicity of root knot (M. incognita) and burrowing nematode (Radopholus similes) has also been proved individually.

20.2

Pathogen:
  • The disease is caused by Fusarium solani Sacc. f.sp. piperi.
  • Mycelium is septate and hyaline at first and becoming cream coloured with age, however, some isolates produce blue or red pigment.
  • Micro conidia are ellipsoidal, straight to curved, one to two celled and hyaline.
  • Macro conidia are hyaline, 3-5 septate, falcate having gradually pointed and curved ends and appear on sporodochia.
  • Chlamydospores, both rough and smooth walled, characterized by thick walls are terminal or intercalary.
Disease cycle and epidemiology:
  • The pathogen is soil borne in nature.
  • It perpetuate in the form of chlamydospores in the soil.
  • It requires high temperature for infection.
  • More damage is done by the organism in association with Meloidogyne incognita than individually.
Management:

i) Application of neem cake @ 1kg/vine reduce M. incognita population under field conditions.
ii) Apply Phorate (3 g a.i./vine) application twice a year for the management of both nematodes.
iii) Mycorrhizal fungi Glomus mossae, G. fasciculatum, Gigaspora margarita and Acaulospora laevis also show varying degree of root knot suppression.
iv) Piper colubrinum is resistant to both root knot and burrowing nematode.


3. ANTHRACNOSE
The disease is also known as “Pollu’. Spike shedding due to this disease can go upto 10 per cent. In early infection, there is up to 77 per cent weight loss of berries while late infection causes 56 per cent infection.

Symptoms:
  • The symptoms on young leaves and spikes appear as small brown specks which are surrounded by yellow halo (Plate-3a).
  • In severe form, defoliation and spike shedding may also occur.
  • Small cracks develop on the berries after the infection has been established, thus reducing the quality of the produce.
  • The infection on tender berries causes darkening of the pericarp and affects their subsequent development (Plate-3b).
  • With time, these dry up resulting in chaffey berries, hence the name ‘pollu’ which means the hollow berry.

20.3

Pathogen:
  • Three species of genus Colletotrichum like C. gloeosporioides (Penz.) Penz. & Sacc., C. necator Masse and C. capsici (Syd.) Butler & Bisby have been reported to be associated with this disease.
  • The mycelium of C. capsici is septate, intercellular as well as intra-cellular and aerial mycelium appears light to dark grey in colour.
  • Acervuli are round and elongated in shape (Plate-4), setae are scattered, brown, 1-5 septate, rigid and swollen at base and acute at apex.
  • Conidiophores are short, hyaline to faintly brown, cylindrical, septate or aseptate.
  • Conidia are falcate, fusiform with acute apices and narrow truncate base, one celled, hyaline and uninucleate.

20.4

Disease cycle and epidemiology:
  • Since the vines are perennial, the disease symptoms appear throughout the season and thus the life cycle of the pathogen continues.
  • Dioscorea triphylla is a collateral host.
  • The pathogen require high humidity in the form of dew, the maximum disease incidence i.e. 28-34 per cent occur during the months of August and September.
Management
i) Sprays of carbendazim or benomyl (0.1%) at 10 to 14 days interval have been found effective in reducing the intensity of this disease by reducing the black spots per berry and also increase berry yield.
ii) Three sprays of Bordeaux mixture (5:5:50) during June-July, late July and late August have also been found quite helpful in reducing the disease.


4. LITTLE LEAF
  • The occurrence of the disease has been reported from Sri Lanka. However, the cause of the disease has not been established but a phytoplasma may be associated with this disease.
  • The symptoms of this disease include chlorosis of leaves, shortening of internodes, proliferation of branches, greening and enlargement of floral bracts.
  • Seeds from infected vines germinate poorly.

5. MOSAIC
  • The virus produces symptoms as chloratic , irregular patches and the leaves are shrunken. Sap inoculation of indicator plants reveal symptoms resembling those of cucumber mosaic virus.
  • The virus is transmitted to young pepper plants by grafting and by aphid Aphis gossypii.

6. STUNTED DISEASE
The disease was first recorded in black pepper nursery at Neriamangalam, Idukki, Kerala during the year 1975 and is now prevalent in Idukki and Wynad districts of Kerala and in Karnataka.

Symptoms:
  • The leaves of the diseased plants become chlorotic having varying degrees of reduction in the size and are crinkled.
  • The internodal distance is reduced and stunting symptoms are produced.
  • Witches broom symptoms are exhibited occasionally on affected vines.
Pathogen:
  • A strain of Cucumber mosaic Virus (CMV) has been identified as one of the causal agents besides, a strain of badana virus.
Disease cycle and epidemiology:
  • Mealy bugs transmit the virus from infected to healthy vines.
  • The disease spread is rapid through planting material.
Management: Selection of healthy vines for transplanting is important.


7. PHYLLODY
  • This disease was first noticed in parts of Wynad in Kerala.
  • The disease is suspected to be caused by Phytoplasma.
Symptoms:
  • The spikes are converted into leaf like structures instead of normal flowers.
  • The production of berries is hampered but the vines are not killed.
Last modified: Friday, 2 March 2012, 5:43 AM