The experiment was conducted at the farmer’s field of Sadar upazila of Patuakhali district, Bangladesh to screen mungbean varieties against flea beetle of mungbean from January to April 2016. It was located in between 22°14' and 22°29' North latitudes and in between 90°12' and 90°28' East longitudes (BANGLAPEDIA: National Encyclopedia of Bangladesh, 2015). It is adjacent to the Bay of Bengal. The area lies at 0.9 to 2.1 metre above mean sea level (Iftekhar and Islam, 2004). 15 mungbean varieties viz., BARI Mung-1, BARI Mung-2, BARI Mung-3, BARI Mung-4, BARI Mung-5, BARI Mung-6, BINA Moog-4, BINA Moog-5, BINA Moog-6, BINA Moog-7, BINA Moog-8, BU Mug-1, BU Mug-2, BU Mug-4 and Patuakhali local Mung were used as study materials. The seeds of these mungbean varieties were collected from Bangladesh Agricultural Research Institute (BARI), Gazipur, Bangladesh Institute of Nuclear Agriculture (BINA), Mymensingh, Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU), Gazipur and Patuakhali local Mung variety collected from farmers’ of Patuakhali.
The experiment was laid out in Randomized Complete Block Design (RCBD) with three replication of each treatment. Each replication represented a block which was divided into 15 unit plots. The individual plot (4 m x 2.5 m) was made ready as per the treatment design. The mungbean seeds were sown on the 29th of January 2016 at the rate of 30 kg ha-1 (BARI, 2011). Within the row, the seeds were sown continuously at a depth of 6-7 cm and covered by loose soil by hand keep. Row to row distance was 30 cm. The fertilizers were applied as per the fertilizers recommendation guide (BARI, 2011). Urea, triple super phosphate (TSP) and muriate of potash (MoP) were applied in the field uniformly @ 50, 85 and 35 kg ha-1, respectively during the final land preparation. The plants were exposed to natural insect pests’ infestation and insecticide was not applied during the experiment.
2.1 Number of Flea beetle: The population of flea beetle was recorded at an interval of 7 days commencing from the first incidence. At the vegetative and reproductive stage, data on a number of flea beetle was collected 5 times (18, 25, 32, 39, 46 DAS) early in the morning (6.30 a.m.-9.00 a.m.). All plants from each unit plot were observed individually.
2.2 Number of infected plants by flea beetle: The total number of infested plants was recorded from the selected 1m2 area of the center of each unit plot to determine the level of infestation by flea beetle. Data on the number of infested plants were recorded at an interval of 7 days commencing from the first incidence. The data were collected 5 times (18, 25, 32, 39, 46 DAS).
2.3 Percentage of leaf area damaged by flea beetle: For collecting data on the percentage of leaf area damaged by flea beetle, the percentage of leaf area damaged by flea beetle from 5 representative leaves of randomly selected 5 plants of each unit plot were measured separately by eye estimation and recorded at vegetative stage.
2.4 Yield data: The selected 1m2 area of the center of each unit plot was kept undisturbed for recording yield data. Mungbean was harvested thrice at 67, 74 and 82 DAS. Mature pods were harvested at 67 DAS when about 80% of the pods became blackish in colour. Second harvesting was done at 74 DAS. Final harvesting (third time) was done at 82 DAS. The harvested pods of 1 m2 area from each unit plot were kept separately. Grains were recorded from 1 m2 area per plot-wise and the yields were expressed in kg ha-1. During the experimental period, meteorological data on temperature and relative humidity were collected from the Patuakhali meteorological office.
2.5 Statistical analysis: The collected data were statistically analyzed through the analysis of variance using Web Agri Stat Package (WASP 1.0). The population data were transformed to square root (√x + 0.5) values. Means were separated by critical difference (CD) values at a 5% level of significance.