Fungal and bacterial heart rots

Fungal heart rot

Fungal heart rots ('top rot' in Australia), as well as root rot of pineapple, are diseases associated with wet environmental conditions. P. cinnamomi Rands requires cool conditions and heavy, wet, high-pH soils. Heart-rot mortality can range from 0 to 100%, depending on the soil type, pH and rainfall. The economic impact of heart rot results from a reduction in plant densities due to plant mortality. However, adjacent plant mortality is partially compensated for by increased exposure of the remaining plants and subsequent increased fruit size (K.G. Rohrbach, unpublished results).

Heart rot can be caused by Phytophthora nicotianae B. de Haan var. parasitica Dast. Waterh., frequently called Phytophthora parasitica Dast. in the pineapple literature, P. cinnamomi Rands and Phytophthora palmivora (Butler) Butler. Heart-rot symptoms are the same, regardless of the Phytophthora species causing them. The most widely distributed species are P. cinnamomi and P. nicotianae B. de Haan var. parasitica (Rohrbach, 1983; Rohrback and Apt, 1986). P. palmivora probably has a much more limited distribution (Boher, 1974; Rohrbach, 1983). Descriptions of the three pineapple pathogens can be found in Waterhouse (1963) and there is a useful key to identification in Newhook and Stamps (1990).

As pathogens of pineapple, P. nicotianae var. parasitica, P. palmivora and P. cinnamomi are not normally found together. P. nicotianae var. parasitica and P. palmivora are found at lower elevations in Hawaii and in the lowland tropics, where optimum temperatures for disease development are in the range of 25-36°C. In contrast, heart rot from P. cinnamomi is found under cooler conditions, such as the higher elevations of Hawaii and the cooler pineapple-production areas, such as Australia, where optimum soil temperatures for disease development are 19-25°C.

An initial heart-rot symptom is the failure of the young leaves to elongate. Later symptoms are yellowing to bronzing of the young leaves, which may then lean to one side of the plant (Fig. 9.20). A slight pull on the young symptomatic leaves will remove them from the plant, confirming the presence of the disease. Phytophthora infections are limited to the stem and basal white portion of the leaves.

The primary inoculum of the three Phytophthora species is chlamydospores, either alone or in infested plant debris in the soil, where they can survive for years. Chlamydospores of P. cinnamomi have been quantified in pineapple soils by sieving (McCain et al., 1967). Inoculum levels of five to ten chlamydospores per gram of soil have resulted in approximately 100% infections in non-pineapple hosts (Mitchell and Kannarischer-Mitchell, 1983). Sporangia produced from chlamydospores can be dissemi

Soil Microbial Inocula

Fig. 9.19. Good (left) vs. poor (right) soil preparation prior to fumigation. Poor soil tilth with large clods results in significant loss of soil fumigant and ineffective nematode control.

Fig. 9.19. Good (left) vs. poor (right) soil preparation prior to fumigation. Poor soil tilth with large clods results in significant loss of soil fumigant and ineffective nematode control.

The Vegetation Heart Causes
Fig. 9.20. Phytophthora heart rot caused by Phytophthora nicotianae var. parasitica.

nated by splashing soil or by aerial wind dispersal. Infection by zoospores of P. nicotianae var. parasitica is most common through the leaf axils of the crown during the first 3-4 months following planting (H. Klemmer, unpublished results). Infection by P. cinnamomi is mostly through the roots, progressing up the root to the stem apex, causing the heart-rot symptom. With P. cinnamomi, germinating chlamydospores or zoospores from sporangia primarily infect root tips. Infection may also occur through the leaf axils. Little evidence exists for secondary spread from infected crowns (Chellemi et al, 1988).

Very little is known about the effects of soil moisture on infection. Infection by P. nicotianae var. parasitica is probably less dependent on high moisture than that by P. cinnamomi (Hine et al., 1964). In citrus, the duration of saturated soil conditions is more important than the frequency. High soil moisture (poor drainage) increases infection by P. cinnamomi but also reduces root growth. H. Klemmer (unpublished results) claimed that infections in the field can take place through leaf axils from soil splashed there and moisture from dews. Soil moistures below 15% reduce germinability of P. cinnamomi chlamy-dospores (McCain et al., 1967).

Bacterial heart rot

Bacterial heart rot of pineapple is caused by the facultative anaerobe E. chrysanthemi Burkh. et al. The disease was first reported in Malaysia but has more recently been reported in Costa Rica (Chinchilla et al., 1979), Brazil (Melo et al, 1974), and the Philippines (K.G. Rohrbach, personal observation). The disease is of major importance in Malaysia but not as important as fruit collapse, caused by the same organism. Recently the disease has become a major problem in the Philippines (K.G. Rohrbach, personal observation).

In Malaysia, bacterial heart-rot incidence varies from 0 to 10% in the 'Singapore Spanish' cultivar and is as high as 30% in the 'Gandul' cultivar (Lim, 1985). Incidence in the 'Smooth Cayenne' cultivar is less because it is more resistant than the 'Spanish' types. Because the plant usually survives infection, the economic loss is attributed to 'out-of-cycle' fruiting on the lateral shoot, which arises from the remaining stem tissue. In mechanized production systems, this 'out-of-cycle' fruit is usually lost.

E. chrysanthemi is a pathogen of a wide range of plants in the tropics and subtropics. This may be due to its ability to grow at higher temperatures than the other soft-rot bacteria. Virulence is related to the ability of E. chrysanthemi strains to produce large quantities of endopolygalacturonic trans-eliminase (Perombelon and Kelman, 1980).

Bacterial heart rot is characterized first by a water-soaked lesion on the white basal portion of the leaves of the central whorl. The infection may spread to include the entire basal portion of all leaves of the central whorl. Spread may occur into the green mid-portion of the leaves, resulting in an 'olive-green' leaf colour and a bloated appearance (Plate 28). If the infection of the green portion of the leaf is arrested, a dark infection border forms (Lim, 1985). Symptoms of fungal heart rots can be distinguished from those of bacterial heart rot by the absence of extension of the infection into the mature green areas of the leaf (see Plate 28).

The main source of inoculum is thought to be infested juice from collapsed fruit. Infested seed material is probably not a major source of spread because bacteria do not survive long on leaf surfaces (Lim, 1985). According to Lim (1985), infection takes place through the stomata and the bacteria can be transmitted to the infection site by insects, most commonly ants (the big-headed ant and the Argentine ant), and by wind and windblown rain. Souring beetles (H. ocularis and Carpophilus foveicollis) have also been shown to be vectors, but are of minor importance (Lim, 1985). In the Philippines, the pineapple tarsonemid mite, S. ananas, has been associated with bacterial heart rot. Feeding by the mite probably produces wounds, because mechanical wounding is observed to increase disease (K.G. Rohrbach, personal observation). In Australia, urease in dirty water breaks urea down to NH4OH, which causes burn and provides a point of entry for the bacteria (D. Bartholomew, personal communication). Plants that are 4-8 months old appear to be the most susceptible to infection. The plant crop is also more susceptible than the ratoon (Lim, 1985). Susceptibility appears to be related to the rate of plant growth, because low leaf water status slows the rate of infection (Perombelon and Kelman, 1980). When environmental conditions are optimum for disease development, the entire disease cycle may occur in 1-2 weeks (K.G. Rohrbach, personal observation).

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Responses

  • bruto
    Which bacteria causes pineapple rot?
    6 years ago
  • annika
    How phytopthora hear rot in pinneapples can be controlled?
    2 years ago
  • antje
    Why pineapple flowers and young fruits rot?
    2 years ago
  • selassie nuguse
    Can bacterial heart rot spread to other plants?
    2 years ago
  • james
    Can fungal bacteria spread on fruit causing it to rot?
    11 months ago
  • semrawit
    How to treat bacterial heart rot fruit collapse?
    1 month ago

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