Nematodes constitute one of the major limiting factors in fruit crop production. They cause extensive root necrosis resulting in serious economic consequences viz.; fertilizers are not effectively utilized, the period from planting to harvesting is extended, drastic reduction in fruit or bunch weights, the quality of fruits is impoverished and fields have to be replanted every 2 to 3 years because of drastic reduction in plant numbers.
Furthermore, roots damaged by nematodes are easy prey to fungi which invade the roots and accelerate root decay. The root-knot nematode Meloidogyne incognita, the burrowing nematode Radopholus similis and citrus nematode Tylenchulus semipentrans are the major nematode pests that infect these fruit crops.
How serious are these nematodes and how does it spread?
These nematodes are responsible for 30 to 40 percent yield losses in various fruit crops. The incidence of fungal pathogens would be doubled in the presence of the nematodes. These nematodes cause breakdown of resistance to fungal diseases in certain varieties of fruit crops. The nematodes spread from one area to another mainly through infested planting materials.
In the case of banana, paring or trimming of suckers, often done before planting is usually not suficient to remove the infections that extend deeply into the sett. This nematode is disseminated when water that drains from infested areas gets recycled into the irrigation system. Soil that adheres to implements, tyres of motor vehicles and shoes of plantation workers may also spread nematodes from one area to another area. Where do these nematodes live? The maximum number of nematodes is present at a distance of 25 to 50 cm from the base of the plant and at a depth of 20 to 40 cm.
What are the symptoms?
These nematodes are parasites of roots or underground stem. The root knot nematode produces galls or knots on the roots. Wounding of roots by the nematodes usually, induce reddish-brown cortical lesions which are a diagnostic symptom of the disease in case of banana. These lesions are seen when an affected root is split longitudinally and examined immediately. Root and rhizome necrosis is manifested by varying degrees of retarded growth, leaf yellowing and falling of mature plants. With the increase in nematode population, feeder roots are invaded and destroyed as soon as they are formed. The resulting setback in the uptake of plant nutrients leads to debility of the plants and production of smaller fruits. The lesions of the primary roots together with the girdling and death of these anchor roots make the plant prone to ‘tip over or topple’ by wind action in case of banana.
Life cycle of the root-knot nematode
After searching a suitable site, normally behind the root cap, the juveniles start feeding on epidermal cells, become sedentary during feeding and enlarge in cross-section. They continue to feed except for 3 and 4 stage juveniles. Third and fourth moults take place in quick succession, thereby leading to the development of pear-shaped, white adult females. The males are elongate and vermiform. The reproduction is normally by parthenogenesis or sometimes by amphimixis. Each adult female lays about 400-500 eggs in the gelatinous matrix. The total time taken for completion of one life cycle under optimum conditions (optimum temp. 27-30OC) is 3-4 weeks in most species depending upon the host and other weather conditions thus leading to completion of several generations in a year
Life cycle of the burrowing nematode
The burrowing nematode has a migratory endoparasitic habit. Although the stages remain vermiform throughout, sexual dimorphism is apparent with adult males being somewhat degenerate and probably non-parasitic. Eggs are normally laid in infested tissue over 7-8 days at the rate of about four eggs per day. The life cycle from egg to egg extends over 20 to 25 days with eggs taking 8-10 days to hatch and the larvae 10-13 days to mature.
Life cycle of the citrus nematode
Tylenchulus semi penetrants exhibit sexual dimorphism, reproduces sexually and occasionally by facultative parthenogenesis without the need of males. From the egg, which contains the first stage juvenile (J1), the second-stage juvenile (J2) emerges and searches for host roots. The motile and vermiform J2 female moults
into the vermiform J3 and J4, and finally into the sedentary adult. The immature female penetrates into the deep cortical layers of the root, becomes sedentary and establishes a permanent feeding site consisting of specialized cells called ‘nurse cells’ which are the main source of nutrients.
Upon maturation, the posterior portion of its body swells and protrudes from the root surface while its elongated neck and head remain embedded into the cortex. Mature females produce eggs that are embedded in a gelatinous matrix. The length of the female life cycle from egg to egg ranges from four to eight weeks. The development of the J2 male into an adult is completed in seven days and does not require feeding. Citrus nematode infected roots are thicker, darker, decayed and show a dirty appearance because of a large number of females sticking on the infected roots. The infected root systems due to the nematode damage lose the ability to absorb enough water and nutrients for normal growth.
Papaya, acid lime seedlings, guava and pomegranate grafts are produced in substrate mixture in polythene bags. Many a times substrate mixture (sand + soil + FYM or any organic manure) harbour above mentioned nematodes and other pathogenic fungi and bacteria. Nursery men don’t treat the soil mixture which is used for the production of fruit seedlings or grafts in their nurseries As such nematode infestation on the seedlings or grafts makes way for the entry of various pathogenic fungi and bacteria. These nematodes and other pathogens multiply in the farmers’ fields. As a consequence, the soil in the farmer’s field becomes sick and unproductive, and ultimately soil becomes the unit for the cultivation over a period if proper measures are not taken to combat these nematodes and other pathogens.
During the process of hardening in banana tissue culture seedlings, owing to the quality of substrate mixture, seedling roots get infected with nematodes such as Meloidogyne incognita, M. javanica (root-knot nematodes), Rotylenchulus reniform is (reniform nematode), Heterodera sp., (cyst nematodes). Further, they are also infected with other pathogenic fungi and bacteria. Once these seedlings are infested the pathogens reach the farmer’s field and cause the diseases in their fields. Need for producing the healthy seedlings or grafts of fruit crops Securing healthy seedlings or grafts is essential to ensure optimum plant population stand, good crop growth and higher yields.
Infestation by heavy populations of nematodes and other pathogens will result in very weak seedlings or grafts with poor root growth. Seedlings or grafts with stunted root system cannot establish well after transplanting. Nematode attack on the root system makes the seedlings or grafts weak and also vulnerable to the infection by secondary pathogens (soil borne fungi and bacteria).
Nematode damage also results in the breakdown of the resistance against pathogenic fungi. Further, infected nematode seedlings facilitate the spread of the nematodes in the main fields making the problem more difficult to manage in a larger area. Because of all these reasons, it is inevitable to produce the seedlings or grafts without the infestation of nematodes or other pathogens. The solution: The IIHR, Bengaluru has developed a biopesticide formulation to manage nematode problem in banana seedlings. This is an organic formulation, consists of Pseudomonas fluorescence and Trichoderma harzianum.
Patents from 4 countries were granted for this innovation. United States (US) patent – No: US 7,923,005 B, Thailand patent – No: 7621, Indian patent – No.250779, Australian patent – No. AU 2007216174 B2 (Innovators: Dr M. S. Rao, Principal Scientist, Division of Entomology & Nematology, & Dr N. Ramachandran, Former Principal Scientist and Head, Division of Pathology, IIHR, Bengaluru).
The institute also developed mass production protocols of Pseudomonas fluorescence 1% W. P. (an effective bio-bactericide and also has nematicidal properties), Trichoderma harzianum 1% W. P. & Trichoderma viride 1.5 % W. P. (effective bio-fungicides and also have nematicidal properties), and Paecilomyces lilacinus 1% W. P. & Pochonia chlamydosporia 1 % W. P. (effective bionematicides). Dr M. S. Rao is the innovator of the technologies.
A method for producing healthy seedlings of banana One ton of soil mixture or any substrate used should be prepared by mixing two kg each of Pseudomonas fluorescens 1% W. P., Trichoderma harzianum 1% W. P.
And Paecilomyces lilacinus 1% W. P. + five kg of carbofuran or phorate or 25 kg of neem cake or pongamia cake. After mixing with all these materials the soil mixture or any substrate can be used for hardening banana seedlings.
Effects of substrate treatment with biopesticides
- It helps in producing the disease free and healthy seedlings
- It helps in promotion of growth of the seedlings
- Because of ISR (Induced Systemic Resistance) effect, it helps in the
management of pathogens
Methods for producing healthy rootstocks/ grafts
One ton of soil mixture (1:1 of red soil and sand) mixed with 500 kg of FYM enriched with 2 kg each of Pseudomonas fluorescens 1% W.P., Trichoderma harzanium 1% W.P., Paecilomyces lilacinus 1% W.P. +50 kg neem or pongamia cake + 5 kg carbofuran or phorate. This substrate should be used for producing healthy grafts or rootstocks of fruit crops. Spraying or drenching the nursery seedlings or grafts with bio-pesticides IIHR patented organic formulation can be sprayed on the seedlings or grafts by dissolving 5 g or 5 ml/lit of water once in 10 days. This formulation can be drenched in the substrate by dissolving 5 g or 5 ml/lit of water, and this can be done once in 10 days.
Spraying or drenching the nursery seedlings or grafts with biopesticides
IIHR patented organic formulation can be sprayed on the seedlings or grafts by dissolving 5 g or 5 ml/lit of water once in 10 days. This formulation can be drenched in the substrate by dissolving 5 g or 5 ml/lit of water and this can be done once in 10 days.
- Indian Institute of Horticultural Research, Bengaluru