Sunday, 14 June 2020

Bacterial disaese in poplar plants

Bacterial disaese in poplar plants

It is a bacterial poplar tree disease in which large spots appear due to stem and branch. Its pathogen Pseudomonas syringae P.V. The syringe is Van Hall.

Bacterial leaf spot and Canker in poplar


Pathogen: Pseudomonas syringae PV. syringe van Hall

Symptoms

  • Leaf Spot: Leaf Spot Disease at Poplar Plant. This disease is found in this stem, branch, and branch. This symptom is seen in dead plants one to two years old where less canker is formed.
  • The leaves of the poplar plant sometimes appear yellow, sometimes forming large spots.
  • Terminal and side shoots turn black with blackback buds, black lesions appear on stem. These grains produce bacteria, which when dried appear as white deposits on the stem.


Host

Populus spp.: All species present in New Zealand are susceptible but leaf spotting is most prevalent on Populus ciliata, P. deltoides, P. szechuanica, P. trichocarpa, P. yunnanensis, and their hybrids.

Salix spp.: All species present in New Zealand are susceptible. Stem and twig dieback is more common than leaf spotting on these species. Alnus cordata—Leaf spotting and twig dieback.

Geographical Distribution

Throughout New Zealand, particularly in localities with high summer rainfall.

Disease Development

Leaf symptoms first appear in spring when temperatures are rising and moisture levels are high. Throughout the growing season, during periods of continuous rainfall, spots are produced on new leaves. For example, a severe attack of Pseudomonas syringae occurred on foliage and stems of poplars growing in a nursery at Aokautere during a 4-month period when rainfall was 64% (194  mm) more than average, and it rained on 52 of that 120  days. Depending on the cultivar, spots may either remain discrete or merge, forming extensive blotches. In poplars, leaf spot is generally more common than stem cankering and is often seen on plants that do not exhibit any other symptoms.


Bacterial leaf spot on a poplar leaf

Fig. Bacterial leaf spot on a poplar leaf.

Bacterial canker on poplar shoot

Fig. Bacterial canker on poplar shoot.

Formation of stem and twig cankers also depends on high moisture levels; however, symptoms vary, and sometimes stems may be roughly fissured or have sunken black lesions oozing bacteria. Sometimes the whole stem is affected, killing the plant; more often only the top one-third to one-half of the plant, or only lateral branches, is involved. When there is extensive shoot and twig dieback with blackened dead foliage the condition is referred to as “blast.” New shoots grow from below the infected areas on stems and branches. Although stem fissures and cankers may heal and the plant continues to grow, this often leaves a weak point that makes the plant susceptible to breakage in high winds.

Some severe outbreaks of the disease occur when sudden frosts follow a warmer wet period. Approximately 50% of P. syringae isolates, tested from poplars and willows in New Zealand were capable of causing ice-nucleation. Ice-nucleating bacteria initiate the formation of ice crystals within host cells during frosts, and the combination of bacteria and frost causes more extensive tissue disruption than if either factor were present independently.

Economic Importance

Losses due to this disease are generally not great. Outbreaks of disease due to P. syringae on 1- and 2-year-old nursery-grown poplars are sporadic and very dependent on prevailing weather conditions. In rare instances, damage can be severe when P. syringae is combined with late frosts.

Control

Control of the disease is generally not warranted. Traditionally, copper-based inorganic compounds have been used to reduce bacterial populations but with only limited success. There is potential for biological control with competitive, nonpathogenic strains of other Pseudomonas species.

Crown Gall in poplar


Pathogen: Agrobacterium tumefaciens

Symptoms

Crown gall caused by Agrobacterium tumefaciens can be a major nursery problem for the production of 1-year-old rooted plants of white poplars. Large galls may form at a ground level causing girdling of the main stem, poor growth, restricted shoot growth, and toppling. Large galls may occasionally form on the trunk of the older trees at the crown level or at first 1-2 m height from the crown level.

Disease Cycle

Crown gall bacterium exists in the soil and infects trees through wounds. The bacterium can be spread by ground-inhabiting insects, rain splash, irrigation, cultivation, pruning, and movement of infested soil particles. The bacterium is also spread from infected to healthy trees when infected trees are pruned or otherwise cut and the contaminated tools are used to prune healthy trees.

Crown Gall in poplar

Fig. Formation of gall at the crown region of a poplar tree. 

Economic Importance

The galls themselves may be considered unsightly. More important is that galls disrupt nutrient and water transport in the vascular tissues, which results in poor growth of young trees. Affected stems are weakened at the points of infection and can be invaded by organisms that cause discoloration and decay resulting in stem breakage.

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