An-Najah Staff

Tomato, considered one of most important and popular crop, was infected by Tomato Yellow Leaf Curl Virus (TYLCV) which causes significant yields loss. Biological and molecular tools were used to evaluate the TYLCV incidence on tomatoes grown under commercial conditions. A total number of 72 tomato plants from each eight different tomato cultivars commercially planted in Palestine were tested for their virus infection which occurred naturally. The virus incidence was reported biologically based on visual inspections for the disease symptoms and molecularly by PCR tests, in two growing season periods: Summer (2006) and spring (2007). As a result, no cultivars were found “immune” to virus infection. However, fundamental differences in symptoms development and severity had been discovered. This study, which was carried out for the first time in Palestine, showed that some cultivars such as “3060” could be targeted as promising virus-tolerant ones. The sensitivity of molecular methods over bioassays was evaluated, and combined methods were suggested for any cultivars resistance assessments. Besides, research results revealed that the experimental conditions in Spring were not in favor of the virus spread, as the main virus vector (Bemisia tabaci) population number would be lower in the Summer season; thus the Spring season is seen as the best one for farmers to escape from TYLCV infections.

AIMS:

To isolate and formulate a native strain of Zoophthora radicans naturally infecting larvae of diamondback moth, Plutella xylostella, existing in South Australia and to provide evidence that formulation of the fungus is effective against P. xylostella larvae, and therefore, it could be used as a tool in pest management of this insect.

METHODS AND RESULTS:

Dose-response bioassays using formulated and unformulated forms of the fungus strain were carried out against third instar larvae of P. xylostella. Results obtained have indicated a significant increase in the larval mortality when higher concentrations of a formulated form of the fungus strain were applied compared to the treatments with the unformulated form (85·0 vs 57·5% of larval mortality, respectively, at the top concentration of 10(7) conidia/ml). The median lethal concentration (LC50) for a formulated form was 100 times less than that of the unformulated form when they were applied against the third instar larvae of P. xylostella. In addition, the formulation used in the present bioassays has preserved the viability of introduced fungus conidia for longer time in comparison with the unformulated conidia.

CONCLUSIONS:

The effective application of a formulated fungus strain against P. xylostella larvae constitutes the first step towards its use in pest management of this insect.

SIGNIFICANCE AND IMPACT OF THE STUDY:

The formulated fungus in inverted emulsion could be used as an alternative tool to insecticides in pest management of P. xylostella larvae because of the development of resistance to insecticides in the treated larvae.