India

Black pepper is affected by several diseases caused by fungi, bacteria, virus and mycoplasma, besides nutritional disorders. Crop losses due to diseases and pests are identified as major causes of low productivity of pepper in India (Sarma and Anandaraj 1997). The earliest record of diseases of pepper in India was that of Barber (1903, 1905). Butler (1906) also recorded the death of pepper and Rao (1929) isolated Phytophthora from diseased pepper, but the etiology remained inconclusive. Ridley (1912) referred to three important diseases of pepper namely, canker, hyphae in vessels and wilt. The cause of wilt was not confirmed but assumed to be due to fungi such as Nectria, Cephalosporium and Fusarium. Menon (1949), while reviewing the diseases of pepper, reported that stump rot was due to Rosellinia bunodes, "pollu" disease caused by Colletotrichum sp. and root disease or wilt due to an unknown pathogen. From the diseased plants Nectria sp. was recorded, but pathogenicity was not proved. Crop losses caused by diseases are a major production constraints in all pepper producing countries. In Brazil root rot and stem blight caused by Fusarium solani f. sp. piperis and the mosaic disease caused by cucumber mosaic virus are the major diseases (Duarte and Albuquerque 1991), whereas, in India, Indonesia and Malaysia Phytophthora foot rot is the major disease (Sarma et al 1992c, Holliday and Mowat 1963, Kueh and Sim 1992d, Manohara et al. 1992). Other diseases include slow decline, anthracnose, viral diseases which are referred to as stunted disease (Sarma et al. 1991), stunted growth (Sitepu and Kasim 1991) and wrinkled leaf disease (Kueh and Sim 1992b). In India, although wilt disease was the major disease causing death of plants, Phytophthora as the causal organism was reported only in 1966 by Samraj and Jose. Several diseases were recorded subsequently and now 17 diseases are known to affect pepper (Sarma et al. 1991).The diseases of pepper are reviewed recently (Sarma et al. 1991, 1994, Anandaraj and Sarma 1995). Among these diseases, Phytophthora foot rot, slow decline which were previously referred to as "quick wilt" and "slow wilt" respectively (Nambiar and Sarma 1977, Nambiar 1978, Das and Cheeran 1986), anthracnose and stunted disease cause severe crop losses. Phytophthora capsici occur both in the nursery as well as in the main field affecting all parts of the plant while others are confined to specific plant parts. Based on the severity of crop losses caused, pepper diseases are classified into major and minor diseases. The major diseases are treated here with greater details.

MAJOR DISEASES

Phytopbthora Diseases in Pepper

Phytophthora capsici occurs on all parts of the plant and cause severe economic damage. The symptom expression depends upon site of infection and extent of damage (Mammootty 1978, Anandaraj and Sarma 1995). Phytophthora infections in pepper is broadly classified into aerial and soil infections. Aerial infection occurs on the runner shoots, foliage, spikes and branches causing blight, spike shedding, defoliation and die back and at times death of plants. Infection on the runner shoots often reach the collar causing foot rot.

Symptoms of foliar infection

On leaves one to many dark spots having characteristic fimbriate advancing margins occur, which later coalesce leading to defoliation even before the lesions spread to the entire lamina. Infections on runner shoots (stolons) that arise at the base of the vines and trail on the ground occur both on the tender leaves and shoots. The fungus sporulates abundantly forming a white covering on the blighted tender shoot. Infection on tender shoots upon reaching the stem, cause, collar infection and sudden wilting of plant. Infection on spikes causes blackening of developing fruits and peduncle. Infection can start on any part of the spike and in due course affected spikes are shed. Infection on branches causes drying and defoliation (Fig. 5.1.1). In Brazil, Fusarium infection on pepper is severe and occur both on stem and root. Infection of root results in destruction of feeder roots leading to flaccidity, yellowing and defoliation. Stem infection results in yellowing and blighting of stem and complete death of plants (Duarte and Albuquerque 1991).

Symptoms on roots and collar

Infection on below ground parts such as roots and collar is fatal. Infections of feeder roots causes their rotting and degeneration resulting in yellowing, defoliation and drying up of plants. Feeder root infection reaches the collar through main roots and causes foot rot (Anandaraj et al. 1994). Pepper being vegetatively propagated, roots arise at each node of the main stem which remain below the soil. If the infection reaches the collar, either through the runner shoots or through the roots closer to the soil level, plants show only wilting symptoms, whereas, infection reaching the collar through roots of the lower nodes leads to yellowing and defoliation before succumbing to the infection. Such plants may remain alive for 2-3 years (Anandaraj 1997).

Etiology of Phytophthora foot rot

Foot rot results in sudden wilting and death of plants and hence the disease was previously referred to as either "quick wilt" or "wilt', and the causal organism was

Figure 5.1.1 Symptoms due to Phytophthora capsici infection on black pepper a. A wilting pepper vine due to collar rot b. Infection of upper tier of roots culminating in collar rot c. Infection on spikes d. Foliar yellowing caused by root rot e. Infection on feeder roots spreading to main roots and collar f. Leaf spot showing fimbriate margins at the advancing edge of lesion

Figure 5.1.1 Symptoms due to Phytophthora capsici infection on black pepper a. A wilting pepper vine due to collar rot b. Infection of upper tier of roots culminating in collar rot c. Infection on spikes d. Foliar yellowing caused by root rot e. Infection on feeder roots spreading to main roots and collar f. Leaf spot showing fimbriate margins at the advancing edge of lesion identified as Phytophthora palmivora var piperis (Samraj and Jose 1966), P. palmivora (Holliday and Mowat 1963, Manmohandas and Abicheeran 1985, Nambiar 1978, Nambiar and Sarma 1977, Sarma and Nambiar 1982, Sarma et al. 1982, Nambiar et al. 1978), P. palmivora MF4 (Ramachandran et al. 1986, Sastry 1982, Sastry and Hegde 1982a, 1982b, 1987a, 14987b, 1991). Foot rot resulting from root infection takes a longer time to kill the affected plants and they remain in the field showing declining symptoms. A method to index the level of infection based on foliar symptoms has been developed (Abraham et al. 1996).

Identity of the pathogen

Phytophthora isolates from infected pepper plants when cultured on carrot agar, incubated for 72 h in dark followed by incubation of culture discs of 1 cm in Petri's mineral solution under fluorescent light for 24 h lead to abundant sporulation. The sporangial ontogeny is umbellate with caducous sporangia. Sporangia are borne on long stalks which were ellipsoidal with tapering base, obvoid or fusiform and with a clear papilla. The mean LxB is 24.6x16.34 ,am, the LxB ratio 2.0-2.05 in 58.5 per cent of sporangia and 1.5-1.8 in the remaining. Based on the sporangial characters, the isolates from foot rot affected pepper plantations are identified as Phytophthora palmivora MF4 (Sarma et al. 1982, Tsao et al. 1985, Tsao and Alizadeh 1988, Manohara and Sato 1992). In Johore region of Malaysia, P. parasitica var nicotianae and P. botryosa are reported to cause sudden wilt of pepper (Varughese and Anuar 1992).

Isolation from soil

P. palmivora MF4 from pepper can be isolated from soil and plant tissues using selective media. Among the selective media tried, PVPH medium (Tsao and Guy 1977) is found to be the best. Direct isolation from soil is not successful always, but, pepper leaf (Kueh and Khew 1982) or pepper leaf discs (Ramachandran et al. 1986) are good baits. The fungus could be isolated by using castor seeds as baits (Sastry and Hegde 1987a, 1987b). Albizia falcataria leaflets when used as baits, the fungus sporulate on the baits facilitating confirmation of positive baiting by direct observation of infected baits and this could be brought into pure culture by plating on selective medium (Anandaraj and Sarma 1990). This technique is also adopted for assaying chemicals applied to soil to control Phytophthora foot rot (Anandaraj and Sarma 1991).

Biology of the pathogen

Growth was studied on potato dextrose agar (PDA), cornmeal agar and oats agar. The effect of temperature on the growth of the fungus was studied at 10°C-35°C. Growth was least at 10°C (6 mm) and abundant at 24°C (46 mm) after 72 h and there was no growth at 35°C. Pepper isolates are heterothallic and oospores are produced when pepper isolates are paired with isolates from cocoa and rubber (Sarma and Nambiar 1982). Oospores are produced when compatible types are inoculated on pepper and incubated in dark at 20°C and also in the presence of Trichoderma viride but, oospores are not produced at 30°C (Brasier 1969, 1978). The production of toxin was studied by culturing the fungus in Bartnicki-Garcia's liquid medium (Ribeiro 1978). Cell free culture filtrate from pepper isolates are reported to cause vascular browning and flaccidity of leaves in bioassay (Sarma and Nambiar 1982).

Taxonomy of pepper Phytophthora

The foot rot pathogen of pepper Phytophthora, has been referred to as P. palmivora in the literature (Holliday and Mowat 1963, Kueh 1979, Nambiar and Sarma 1977, Sarma and Nambiar 1982). As the isolates are different from the typical P. palmivora, it was called as an atypical P palmivora (Waterhouse 1974), and was named P. palmivora MF4 in the revised tabular key by Stamps et al. (1990). Most Phytophthora isolates from pepper have an umbellate sporangial ontogeny with long caducous sporangia resembling that of P capsici (Tsao et al. 1985). After detailed morphological and biochemical studies, P. palmivora MF4 was merged with P. capsici as most isolates from pepper resembled P. capsici. The species was redescribed (Tsao and Alizadeh 1988, Tsao 1991) and is currently named P. capsici. Phytophthora isolates from pepper from Indonesia belong to both A1 and A2 mating types (Kasim and Prayitno 1979, Manohara and Sato 1992, Bandra et al. 1985). In India, during the International Pepper Community Workshop in Goa, it was decided to refer this disease as Phytophthora foot rot and the organism as P. capsici (Nair and Sarma 1988). Since then extensive biochemical studies of P. capsici collected from all over the world have revealed the presence of three electrophoretic types Cap1, Cap2 and Cap3 (Oudemans and Coffey 1991). Based on analysis of 113 isolates of P capsici for morphological, physiological and isozyme data for 18 loci for 15 enzymes, two sub groups CapA and CapB were recognized. Indian isolates from pepper have been reported to belong to both sub groups (Mchau and Coffey 1995). Holliday (1998) in his Dictionary of Plant Pathology (2nd edition) designated it as P capsici f. sp. piperis, as this only attacks Piper and therefore differs from the f. sp. capsici which is mainly on Capsicum but has a much wider host range.

Crop loss

In India, pepper is traditionally grown in the Western Ghats, in the states of Kerala, Karnataka and Tamilnadu, recently it is introduced to non-traditional areas of Andhra pradesh and North Eastern States. Foot rot has been reported from the introduced areas such as Tripura (Sarkar et al. 1985). The crop losses due to foot rot of pepper is reported to range up to 30 per cent (Samraj and Jose 1966, Nambiar and Sarma 1977). Crop loss surveys conducted during 1982-1986 in two major pepper growing districts of Kerala (Calicut and Cannanore) has shown that 3.4 per cent and 9.4 per cent of the plants respectively are lost annually amounting to a corresponding production loss of 118 and 904 tons (Balakrishnan et al. 1986, Anandaraj et al. 1989a, 1989b). Every year farmers replant to compensate for the loss of plants, not only due to disease but also due to drought. The annual crop-loss due to foot rot in Cannanore district of Kerala remains the same as indicated by the recent survey report, with an estimated loss of 9.2 per cent (Prabhakaran 1995). Foot rot takes a heavy toll in all pepper growing countries and 5-10 per cent loss has been reported in Malaysia and up to 95 per cent loss in individual gardens (Kueh and Sim 1992a), similar situation prevails in India also.

Spatial pattern of foot rot spread

Nambiar and Sarma (1982) studied the pattern of spread of foot rot disease within a garden over a period of six years and found that the disease spread is in centrifugal pattern from the source of inoculum. The initial occurrence and subsequent spread of foot rot was monitored over a two year period in a pepper plantation at Indian Institute of Spices Research farm, Peruvannamuzhi and the data were analysed using Spatiotemporal distance class analysis developed by Nelson (1995a, 1995b). The analysis indicated that both initial occurrence and subsequent spread followed a strictly non-random pattern and the infection clustered around the previously infected plants (Anandaraj 1997) suggesting the role of initial infection serving as the source and focus of subsequent spread (Zadocks and Van den Bosch 1994). The root infection culminating in foot rot has a long incubation time and takes nearly 23 rainy seasons. During this time the infected plants remaining in the gardens with decline symptoms serve as a source of inoculum for subsequent spread. The foliar infection spreads within the bush through rain splashes from the lower portions to upper portions, whereas, spread to the adjacent plants is through both rain splashes and also through wind blown water droplets (CPCRI 1986, Ramachandran et al. 1988c).

Influence of weather on disease incidence

Aerial infection results in defoliation and in severe cases death of plants. The spread is dependent on the prevalence of favourable weather. The occurrence and spread of foliar infection was studied in an arecanut-pepper mixed cropping system and correlated with the weather factors. A combination of factors such as daily rainfall of 15.8-23.0 mm, temperature range of 22.7-29.6°C, relative humidity of 81-99 per cent and sunshine 2.8-3.5 h /day favour the spread of aerial infection (Ramachandran et al. 1988c, 1990). In the soil phase, the pathogen activity is confined to the wet monsoon period and depend upon the availability of soil moisture (Anandaraj 1997). The onset of monsoon season also triggers the growth of pepper plants through production of new foliage and roots, maximum being in July when the South West monsoon is at its peak. The weather conditions during monsoon along with high soil moisture (>25%), temperature ranging from 22-29°C, relative humidity >80 per cent, are favourable for rapid multiplication of the fungus

(Anandaraj 1997). Attempts were also made to correlate the occurrence of Phytophthora foot rot with the weather conditions (Nair et al. 1988, Mammotty et al. 1991). Since root rot culminating in foot rot has a very long incubation period, correlation of weather factors recorded at the time of observing foliar symptoms may not be a correct indication of the weather requirements for disease development.

Role of weather on the growth of pepper plants

Pepper plants being perennial, the growth also depends upon the availability of soil moisture. The production of new foliage was monitored in two cultivars of pepper, Karimunda and Panniyur 1, by tagging the fruiting lateral branches and counting the new leaves. Highest leaf production occurred in July in both the cultivars (Fig. 5.1.2).

Figure 5.1.2. Proportion of new leaves to old leaves observed and expected for two-year period.

a) Karimunda first year b) Panniyur-1 first year c) Karimunda second year d) Panniyur-1 second year

Figure 5.1.2. Proportion of new leaves to old leaves observed and expected for two-year period.

a) Karimunda first year b) Panniyur-1 first year c) Karimunda second year d) Panniyur-1 second year

Apr May June July Aug Sep Oct Nov Dec Jan Feb

Apr May June July Aug Sep Oct Nov Dec Jan Feb

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2000

2000

Apr May June July Aug Sep Oct Nov Dec Jan Feb

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Apr May June July Aug Sep Oct Nov Dec Jan Feb

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Figure 5.1.3 Feeder root production in pepper. a) At three distances b) At three depths

Feeder root production was estimated by soil core method by collecting soil cores at 20, 40 and 60 cm away from the base of the vine and at 20, 40 and 60 cm depth at each distance at monthly intervals. Highest feeder root production was in July and the feeder roots were concentrated at 0-40 cm from the base of the vine upto 40 cm depth (Fig. 5.1.3). A similar pattern of feeder root concentration was reported from Indonesia. Ipor et al. (1993), while studying root architecture of pepper in Indonesia, recorded 63.8 per cent of feeder roots in the top 0-50 cm. Thus, production of the most susceptible tender tissues, both foliage and feeder roots, occur at the peak monsoon season (Anandaraj 1997). The wet monsoon season in India, not only activate the pathogen but also affects the growth of the host plant. Growth of host indirectly influence the pathogen by the increased root exudation and availability of more susceptible tissues for colonization.

Survival

In the soil phase contaminated soil is the main source of inoculum. The inoculum survives in the soil up to 19 months in the absence of host plant (Kueh and Khew 1982, CPCRI 1986). The soil inoculum was monitored by Ramachandran et al. (1986) in a pepper plantation by collecting soil samples at various depths and distance from the infected vine. The study has shown that the pathogen was concentrated on the surface 0-30 cm and it gets reduced as the distance and depth increase from the source of diseased plant. The main survival structures of P. capsici in the soil are chlamydospores and thickened mycelium (Anandaraj 1997). Soil moisture was found to have a positive correlation on the activity of the fungus in soil. P. capsici has a low competitive saprophytic ability, hence addition of organic amendments to soil promotes growth of saprophytic organisms which in turn reduce the populations of P. capsici (Anandaraj 1997). Production of oospores under laboratory conditions and their possible role in the disease have been suggested (Sastry 1982, Sastry and Hegde 1987a, 1987b, 1988, Santhakumari 1987). Trichoderma viride stimulate oospore formation and also when two compatible types are inoculated on to pepper (Brasier 1969, 1978, 1991). However, oospores as resting structures in infected plant tissues has not been recorded from India. Oospores as survival structures have been recorded in Sarawak and were found to be viable after passing through the alimentary canal of snail (Kueh and Khew 1982). A technique for germinating the oospores of Phytophthora by passing the oospores through the guts of snail has been suggested (Dutta et al. 1984).

Disease resistance

Screening the germplasm of pepper is done adopting stem and root inoculation techniques (Nambiar and Sarma 1979, Sarma et al. 1994). Root inoculation is done by dipping the root system in zoospore suspension while the stem inoculation consists of inoculating the fungus at the third internode of a pepper cutting with 4-5 leaves. The fungus, in the form of 5 mm diameter mycelial disc cut from the edge of a 48 h old culture, is placed at the third internode with a pin prick and covered with moist cotton wad and incubated in humid chamber. Observations are recorded after 72 h on the lesion size and depth of penetration. The lesion size range from 5 mm-120 mm, and depth of penetration can confine to surface or can lead to the rotting of the entire internode. After 72 h of incubation under humid conditions, those cuttings showing lesion size of less than 5 mm and penetration restricted to the surface are rated as tolerant and preserved for future work. In India, all the cultivated germplasm are susceptible to this disease. Among the cultivars, Narayakkodi, Kalluvally, Balankotta, Neelamundi, Mundi and Uthirankotta have been identified as tolerant (Sarma and Anandaraj 1997). Among other taxa, Piper colubrinum, a distant South American species, is highly resistant to P. capsici. Several open pollinated progenies of Perambramundi, Kalluvally Cholamundi and hybrids involving Panniyur 1xKarimunda, and NarayakkodixNeelamundi have recorded tolerant reaction (Sarma et al. 1994). In Malaysia, Cheriakaniakadan and Balankotta were less susceptible than Kuching. Whereas in Indonesia cvs. Kalluvally, Palau Lauta, Belantung, Bangka, Natar I, Merefin, Banjarmasin and Duanteber were rated as less susceptible (Sitepu and Kasim 1991, Manohara et al. 1992). In India, currently, researches are directed to understand the mechanism of tolerance to P. capsici. Among the biochemical parameters, the ratio of total phenols to orthodihydroxy phenol (OD phenols) was higher in susceptible cultivars than in tolerant cultivars. Higher peroxidase activity was recorded in P. hirsutum, a Phytophthora resistant line, and low levels in Daun Leber, a susceptible cultivar (Rahayuningsih 1990). Regeneration protocol for pepper has already been developed so as to attempt biotechnological methods for transferring resistance to the cultivated varieties (Shaji et al. 1995a, 1995b, 1996, Sarma et al. 1996).

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