Effects of Organic Wastes, Glomus intraradices and

Z.A. Siddiqui and M.S. Akhtar (2008) Phytoparasitica 36(5):460-471

Effects of Organic Wastes, Glomus intraradices and Pseudomonas putida on the Growth of Tomato and on the Reproduction of the Root-knot Nematode Meloidogyne incognita
Zaki A. Siddiqui and M. Sayeed Akhtar

Effects of organic wastes (biosolids, horse manure, sawdust and neem leaf litter [NLL]), an
arbuscular mycorrhizal (AM) fungus Glomus intraradices, and a plant growth-promoting
rhizobacterium Pseudomonas putida, were studied on the growth of tomato and on the
reproduction of Meloidogyne incognita. Pseudomonas putida and G. intraradices promoted
tomato growth in nematode-infected and nematode-free plants but growth promotion was
higher in the infected ones. When P. putida and G. intraradices were applied together, the
increase in tomato growth was greater than when either agent was applied alone. Of the
organic wastes, NLL was better in improving tomato growth of nematode-infected plants
followed by biosolids, horse manure and sawdust. Combined use of NLL with P. putida plus
G. intraradices was best in improving growth of the infected plants. Root colonization by
P. putida was increased more when inoculated with G. intraradices than when inoculated
singly. Of the organic wastes, use of sawdust with P. putida caused a greater increase in root
colonization by fluorescent pseudomonads followed by NLL, horse manure and biosolids.
Nematode parasitism had an adverse effect on root colonization by P. putida. Inoculation of P.
putida and organic wastes increased the root colonization caused by the AMfungus. P. putida
was better in reducing galling and nematode multiplication than G. intraradices, whereas use
of the two together was better than that of either of them alone. Among organic wastes,
NLL was better in reducing galling and nematode multiplication followed by biosolids, horse
manure and sawdust. Combined use of NLL with P. putida plus G. intraradices was better in
reducing galling and nematode multiplication than any other treatment.
KEYWORDS:Arbuscular mycorrhizal fungus; biosolids; growth-promoting rhizobacterium;
horse manure; leaf litter; nematode control; sawdust.

Host specificity

AM associations occur in a wide range of distribution among the tropical and temperate regions. They are known not to occur only in a few plants, namely members of the families Amaranthaceae, Pinaceae, Betulaceae, Cruciferae, Chenopodiaceae, Cyperaceae, Juncaceae, Proteaceae, and Polygonaceae. The ectomycorrhizas, on the other hand, occur primarily in temperate forest species, although they have been reported to colonize a limited number of tropical tree species.

Functions of mycorrhizal fungi

AM fungi absorb N, P, K, Ca, S, Cu, and Zn from the soil and translocate them to associated plants. However, the most prominent and consistent nutritional effect of AM fungi is in the improved uptake of immobile nutrients, particularly P, Cu, and Zn. The fungi enhance immobile nutrient uptake by increasing the absorptive surfaces of the root through diffusion.
Enhanced nutrient uptake by AM fungi is often associated with dramatic increase in dry matter
yield, typically amounting to several-fold increases for plant species having high dependency on mycorrhiza.
AM fungi may have biochemical capabilities for increasing the supply of available P and other immobile nutrients. These capabilities may involve increases in root phosphatase activity, excretion of chelating agents, and rhizosphere acidification.
AM fungi are often implicated in functions which may or may not be related to enhanced nutrient uptake. For example, they have been associated with enhanced chlorophyll levels in leaves and improved plant tolerance of diseases, parasites, water stress, salinity, and heavy metal toxicity. Moreover, there is increasing evidence that hyphal networks of AM fungi contribute significantly to the development of soil aggregates, and hence to soil conservation.

SYMPTOMS OF PLANT DISEASES

Any change external or internal in the host plant which serves to recognize the disease is called symptoms. The most important type of symptoms is as follows.

I. Necrosis: It includes death of the infected tissues. The different necrotic symptoms are as follows.

1. Wilts: In wilts, the host plant loses water and gets dehydrated.
2. Damping off: The tissues at the base of the stem in young seedling collapse and degenerate leading to their death in this region.
3. Rot: In rot, the affected tissues are completely disorganized leading to their death in this region.
4. Streak or Stripes: In stripes, the affected tissue appears in the form of elongated and narrow lesions.
5. Canker: canker is the sunken necrotic lesions developed in cortical tissue of stem, leaf and fruit.
6. Spot: Spot is produced due to death of localized region in the root, stem or leaf.
7. Blight: Blight is the burnt appearance due to sudden death of a plant or its organ.
8. Die-back: It is charaterised by dying of plant organs, especially stem or branches, from tio backwards.

II. Hyperplasia (Hypertrophy): It includes increase in cell division or increase in cell size leadind to outgrowth. The different hyperplasia symptoms are as follows;

Galls: Galls are globose, elongated or irregular malformation or outgrowth developed on the affected part of the host plant. Small galls are called warts or tubercules, while larger one are called knots.
Pocket or Bladder: Bladders are formed when the affected fruit is considerably enlarged, distorted and often hollowed to form pockets.
Curl: Curl is formed due to hypertrophy in localized area of the leaf.
Witches broom: It is closely grouped clusters of fine slender braches generally arranged parallel to one another.
Floral abnormalities: The floral parts of some host plants are enlarged and become fleshy and leaf like due to the infection of certain fungi.

III. Hypolysia (Dwarfing or atrophy): This is the reduction in the size of plant parts. The different dwarfing is as follows:
Chlorosis: Poor development of chlorophyll leads to chlorosis. It is caused due to low temperature, mineral deficiencies or certain infections.
Variegation: It is appearance of white or yellow spot in the green chlorophyllous region of the infected leaves.
Stunting: It is caused due to stunting growth leading to dwarfing.
Mosaic: It is development of light green or yellow patches with dark green pathches.
Rossetting: It is caused due to shortening of the internodes of shoot. It leads to crowning of the foliage in cluster assuming in rosette form.
Vein-clearing: It is caused due to yellowing of tissue near the vein.