Rationale

Monitoring studies revealed that H. phycitis, which is found in large number (74 % of the total catches) on Omani lime trees is considered as the prime suspected vector of WBDL. This insect is seen mostly during the winter months (early November to March end). In addition to this 12 other hopper species were also found associated.  But among these, three hopper species are seen in relatively large number on Omani lime. They are Toya sp, Circulifera haematiceps? and one belong to the sub-family  Deltacephalinae. They were also found positive to PCR test. It is therefore, necessary to confirm the candidature of H. phycitis and also the vector ability of the three other hopper species.

Objective

To search the vector(s) of WBDL.

Location

Agriculture Research Center, Rumais.

Duration

Three years.

Materials and Methods

1. H. phycitis adult and other hopper species (candidate vector # 2, 3 and 4) collected from field at monthly interval will be released on potted plants in a cage for sufficient time (15 – 20 days) to ensure that the insect might have transmitted the disease. These pots will be first tested by PCR to ensure that the plants are healthy. After the inoculation feeding, the insects which remain  alive will be removed and the plants will be maintained in greenhouse for two to three years to see the development of any disease symptoms. Equal number of pots from the same batch will be kept in isolation as untreated control.  Attempts will also be made to collect the leaves of the infected plants for PCR test. The insect release will be carried at least for a period of one year. A batch of the collected insects will be tested for the presence of phytoplasma in the body and head. 

Laboratory  involved

Biological control laboratory and Bio-Technology.

Team workers

Dr. Syed Ali Razvi, Rashid Al-Shidi,  Ibtehal Al-Reesi, Ahmed Al-Mandari and Najma Mahmood Al-Zadjali.

Observations

1. Leaf samples for PCR test.

2. Regular observations of the infested plants for the symptoms of WBDL.

Rationale

Experiments conducted so far at Agricultural Research Center, Rumais, Ministry of Agriculture and Fisheries, confirmed the presence of  phytoplasma (Candidatus Phytoplasma aurantifolia) the causal agent of witches’- broom disease of lime (WBDL) in the body of the candidate vector  H.  phycitis. But from the  results on the transmission studies, not all the plants were found positive to PCR. From the work done elsewhere about the phytoplasma (Flavescence doree) in the vector (Elscelidius variegates) showed that the hopper was infected (positive to PCR) through out the year with no specific season pattern. In the saliva, however, no phytoplasma could be detected in autumn (Tanne et. al., 2001). This indicate that the H. phycitis also, probably may not remain infective through out the year.

It was also reported (Tanne et. al., 2001) that the phytoplasma was detected in the body of Elscelidius variegates  three weeks before it was detected in the feeding medium, reflecting that it takes three weeks for the phytoplasma to reach salivary glands.   

After acquisition  feeding, multiplication and movement of the phytoplasma in the gut and haemoceil and  then penetration of the phytoplasma in to the salivary glands is a prerequisite to transmission. Biological transmission assays are, therefore, the only way to ascertain phytoplasma transmissibility. However, they are tedious and time consuming. Therefore, a  polymerase chain reaction (PCR) based method is to be developed for the  detection of phytoplasma in insect - feeding medium (sucrose) that would reflect the vectoring ability by detection it in the insect saliva.

Objective

To know the  season during which the hopper becomes infective.

Location

Agriculture Research Center, Rumais.

Duration

Three years.

Materials and Methods

Adult H.phycitis will be collected  directly from WBDL infected trees. The insects collected will be released on feeding medium. Later the feeding medium will be tested for PCR test.  Similarly the test will be repeated with the other three species of hoppers which are found associated with Omani lime.

Laboratory  involved

Biological control laboratory and Bio-Technology / Plant Pathology.

Team workers

Dr. Syed Ali Razvi, Rashid Al-Shidi, Ibtehal Al-Reesi, Ahmed Al-Mandari and Najma Mahmood Al-Zadjali.

Observations

PCR test to detect the presence of phytoplasma in the feeding medium.

Rationale

Since electron microscopy is a very important tool to see the presence of phytoplasma in plant or insect body, it is to be used for confirmation  after the molecular  diagnosis, which indicates the presence of phytoplasma in the feeding medium of suspected vector(s). The suspected vectors are the candidate vectors # 1, 2, 3 and 4.

Objective

To search the vector(s) of WBDL.

Location

Agriculture Research Center, Rumais.

Duration

Three years.

Laboratory  involved

Biological control laboratory and Electron microscopy College of Medicine.

Team workers

Dr. Syed Ali Razvi, Rashid Al-Shidi and Najma Mahmood Al-Zadjali.

Observations

Phytoplasma in the salivary glands of the candidate vector(s).

Rationale

Certain Citrus species such as sweet lime (Safarjal), sour orange (Naranj), Cleoptera mandrin, Volcamriana, Taheti etc were found free from the symptoms of WBDL in the field survey. They   were also found resistant to the disease in the laboratory as confirmed by challenge grafting. Some of these plants are now in use as rootstocks over which Omani lime is being grafted as scion. It is yet to know whether these root stocks have any role in imparting any degree of resistance to the Omani lime, which is used as scion. This may help in developing a suitable management strategy in the rehabilitation of acid lime in Oman.

Objective

To know the reaction of certain citrus species as root stock in imparting resistance to Omani lime against the phytoplasma (Candidatus phytoplasma aaurantifolia) the casual agent of WBDL.  

Location

Agriculture Research Center, Rumais.

Duration

Three years.

Materials and Methods

Four Citrus species namely sour orange, sweet lime, volcamriana and cleoptera mandrin were taken as root stock and Omani lime  as scion was grafted on  these root stocks. In addition to this, Omani lime as susceptible check and Chinese lime as resistant check were also planted in field during February 2004 in RBD replicated five times. The plants are growing under a package of horticultural practices.

Laboratory  involved

Biological control laboratory.

Team workers

Dr. Syed Ali Razvi, Rashid Al-Shidi and Najma Mahmood Al-Zadjali.

Observations

1. Regular observations of the plants for the symptoms of WBDL.

2. Collection of hoppers coming on different treatments.

Rational

The survey conducted in the recent past  indicated that there is a hybrid  (Citrus aurantifolia x Kamquat) called Chinese lime (also called as Pakistani lime) free from the symptoms of WBDL. This cultivar may be resistant to the disease or have a strong non-preference to the vector of the disease or may be a symptom less carrier. In all cases it looks to be good cultivar to be propagated. This give encouragement for further survey to search lime plants which could show some degree of resistance to WBDL. Taheti (resistant strains to wood pocket ) is recommended  as alternate to Omani lime.

Objective

To search strains of acid lime which could show some degree of resistance to WBDL.

Location

Batinah region.

Duration

Two years.

Materials and Methods

Intensive survey will be done in various farms in Batinah region to search lime plants which are free from WBDL.

Laboratory  involved

Biological control laboratory and Plant Pathology.

Team workers

Dr. Syed Ali Razvi,  Rashid Al-Shidi and Najma Mahmood Al-Zadjali.

Observations

1. PCR test of the young leaf samples (new flush) formed on the Marked plant.

2. Symptoms of WBDL appeared on the marked plant.

Rational

During the survey conducted in the year 2000 and 2001, it is seen that in certain farms where the farmers have taken certain cultural practices like irrigation through bubbler, double basin around the trunk, spacing between plants, weed control and mulching and management measures like fertilizer application, nibbling and timely insecticide sprays, the disease is delayed. In farms where the diseased has already appeared the plant could able to survey for more than the expected period and gave reasonably good yield. To confirm the impact of certain of these treatments, the experiments are planned.

Objective

To know the impact of certain cultural and management practices in controlling WBDL and its vector H. phycitis.

Location

Private farm in Musannah.

Duration

Three years.

Materials and Methods

  A field experiment was laid out in RBD in April 2001  in two plots as Plot-I and Plot-II, each comprising of 28 healthy  Omani lime plants at a private farm in Musannah with age one and two years, respectively. There are seven treatments replicated four times. The treatments are:

T1 = Control

T2 = Nibbling

T3 = Spraying insecticide

T4 = Fertilizer  application

T5 = Fertilizer  application + Nibbling  

T6 = Fertilizer  application + Spraying insecticide

T7 = Fertilizer  application + Nibbling + Spraying insecticide.

Laboratory involved

Biological control laboratory and Soils laboratory.

Team workers

Dr. Syed Ali Razvi, Salim Rasbi and Rashid Al-Shidi.

Observations

The plants will observed at different intervals for the symptoms of WBDL if any. Collection of all the  insects including hoppers which were found attacking the Omani lime plants with the help of suction machine. Sorting out the insects for vector search. Record of certain growth parameters to know the affect of fertilizer application. Leaf sample analysis for macro and micro-nutrient deficiencies and spray of micro-nutrients for plant recovery.

Yield of fruits

To be recorded at each harvest.

Rational

It is reported earlier that there are certain rutaceous plant as alternate hosts of WBDL by graft transmission studies. However, still many are to be tested. Further there  are certain non-rutaceous plants reported as hosts based on some symptoms during survey (1994 - 97) and positive to ELISA  tests. These were not confirmed by dodder transmission and exhibition of  symptoms.  Back transmission is a must to confirm the results.

Objective

To search the alternate host plants  of WBDL.

Location

Agriculture Research Center, Rumais.

Duration

Three years.

Materials and Methods

Laboratory  experiments will be conducted to screen the suspected plants as hosts of WBDL. Such plants are grown in pots in green house and will be exposed to dodder grown on WBDL infected plants.

Laboratory involved

Biological control laboratory and Plant Pathology.

Team workers

Dr. Syed Ali Razvi, Rashid Al-Shidi and Najma Mahmood Al-Zadjali.

Observations

The plants will observed at different intervals for the symptoms of WBDL.

Rationale

Compounds like terpenes, phenols, alkaloids etc are known to impart resistance to plants against certain pests and diseases. Chemical analysis of leaves of resistant and susceptible cultivars may able to understand  the chemicals imparting resistance. This information may help to develop strategy for imparting resistance to Omani lime.

Objective

To known to the chemical(s) imparting resistance to citrus plants against WBDL.

Location

Agriculture Research Center, Rumais.

Duration

Three years.

Materials and Methods

Chemical analysis of  leaves will be done in few selected resistant and susceptible Citrus spp, to know the chemical(s) which are imparting resistance to the plants against WBDL. The experiment will be done in collaboration with SQU.

Laboratory  involved

Biological control laboratory and SQU. (Awaiting for the reply from SQU by  Dr. Iqrar Khan ).

Team workers

Dr. Syed Ali Razvi, Rashid Al-Shidi and Najma Mahmood Al-Zadjali and SQU nominee.

Observations

Collection of samples of leaves of resistant and susceptible Citrus spp and testing the chemicals present and responsible for resistance to WBDL.

Rationale

Terpenes are known to impart resistance to plants against certain pests and diseases. However, it effectiveness in controlling the phytoplasma  is not known. It is therefore felt necessary to study it effectiveness in controlling the phytoplasma causing WBDL.

Objective

To test the efficacy of terpenes in checking the expression of WBDL symptoms when applied as prophylactic measures.

Location

Agriculture Research Center, Rumais.

Duration

Three years.

Materials and Methods

A detail experiment will be conducted in field to test the effectiveness of terpenes in controlling WBDL. The terpenes will be applied at different  doses both as prophylactic and curative measures. Omani  lime will be used as test plant.

Laboratory  involved

Biological control laboratory and SQU

Team workers

Dr. Syed Ali Razvi, Rashid Al-Shidi and Najma Mahmood Al-Zadjali and SQU nominee.

Observations

The plants will observed at different intervals for the symptoms of WBDL if any.

Rational

The common and persistent problem of green house cucumber crop is whitefly (Bemisia tabaci). Both the adults and nymphs suck plant fluids. Since the whitefly has developed resistance to a large number of insecticides and since the use of insecticide has got its own limitations, it is imperative to look for an alternate method that should be safe and efficient. One of which is to develop an efficient trap cropping system against whitefly.

Objective

To develop a trap cropping system, a component of IPM, for cucumber crop grown  in greenhouse against major pests..

Location

Green house at a private farm at Barka.

Duration

Two to three seasons.

Materials and Methods

1. Growing cucumber nursery under agril cover.

2. Eggplant / musk melon (potted plants) will be arranged at the back and on two adjacent sides of GH.

3. A small YST will be hanged to each potted trap plant .

4. YSTs will also be hanged on cucumber plants inside the GH.

Laboratory involved

Bio-control.

.

Team workers

Dr. Syed Ali Razvi, Rashid Al-Shidi and Najma Mahmood Al-Zadjali

Observations

Whitefly  counts at weekly intervals on YSTs and also on leaves of main crop and also on trap crops.

Aphid observations by grading the plants on scale of 0–5.

Mite population count on randomly selected leaf samples.

Rational

The fruits of pomegranate (Punica granatum) is attacked by pomegranate butterfly (Virachola livia). This  is a polyphagous pest having a wide range of host plants such as plums, peaches, mulberry, litchi, sapota, guava, tamarind, pears, citrus, ber, anola and apple. The female lay shiny oval shaped eggs in the calyx of  flowers or small fruits. The egg, larval and pupal periods are 7-10, 17-45 and 7-34 days, respectively.  The caterpillar damage the fruits by riddling through the ripening seeds of pomegranate. As many as eight caterpillars are seen in a fruit. Pupation takes place in side the fruits but occasionally out side also. There are four over lapping generations in a year. This pest can damage 40 -  90 %  of the fruits.

The eggs of this are known to be parasitised by Trichogramma brasicae. The parasitoid was found effective to control the pest but could not stablish. As a result frequent release is a must. Further there is one Trichgramma species found locally which if multiplied and released could perform better. Keeping this in view technique is to be developed for mass rearing of this parasitoid.

Objective

To develop an effective biological control program for pomegranate butterfly Virachola livia.

Location

Rearing of the local parasitoid at the biological control laboratory, Rumais and its release at Jabal Al-Aqdhar.

Duration

Two years.

Materials and Methods

Mass rearing technique of Sitotroga  cerealella and Corcyra cephalonica are established in the laboratory. The eggs of these insects are in use for the rearing of Trichogramma species. This is a very important egg parasite of a number of insects and are to be evaluated for their effective against pomegranate butterfly eggs. The locally available Telenomus sp species will be collected and attempts will be made to develop its rearing technique. In the next step attempts will be made to rear it on large scale for release in Jabal Al-Aqdhar for biological control of pomegranate butterfly Virachola livia.