Abstract
Mustard is an important oil crop. Aphid infestation and drought are the major problem in its expected production. Experiments were organized to find out the drought tolerant mustard varieties, to explore the relationship between aphid infestation and water stress on mustard crops and also to determine the levels of various bioactive compounds in mustard varieties. Plants were grown in pots maintained with 3 levels of water i.e., control (100% FC) and water stress (50% FC and 30%FC), and also evaluated with aphid infestation over control. Besides, aphid infestation status was studied at well-watered condition (100% FC) in field. These experiments were carried out in the laboratory of the Departments of Entomology and Biochemistry and Molecular Biology, BAU, Mymensingh; the experimental field and laboratory of Entomology division, BINA and laboratory of Soil Science and Post- Harvest division, BARI, Gazipur during the period from September 2015 to August 2017. Early Crop maturity (up to 14 days) and reduction of Relative Water Content (up to22.90%) was observed due to severe water stress. Reduced number of branches, less height of plants (up to 30%) and lower yield (up to 63%) were found due to effect of drought. Varieties of Brassica juncea showed late maturity compared to those of B. campestris, however varieties of B. napus and B. juncea were found more tolérant to drought. Plant height and yield were recorded higher in the varieties of B. juncea. The aphid multiplication rate was maximum at the vegetative stage which gradually declined at flowering to pod formation stage. It was also observed that the flowering and pod formation stages were more sensitive for aphid infestation. Depending on varietal variation, 5.83 to 50.83% and 9.20 to 58.63% plants were found infested by aphids at flowering and pod formation stages respectively. The varieties of B. napus were less vulnerable to aphid infestation than those of B. campestris and B. juncea. Aphid feeding and honeydew secretion were more in susceptible varieties and negatively affected by water stress. An adult mustard aphid weighed by 732.07ug and produced on an average 1.18 offspring daily (based on varietal variation). Aphids took phloem sap daily from the plants more times of their body weight. Severe drought stress significantly reduced the reproductive performance (approximately 21%) and body weight of aphid. The reproductive performance was higher and mean body weight of aphids was recorded lower in susceptible varieties. More offspring production by aphid resulted lower unit body weight. Further, due to aphid infestation, increment in proline, total phenol and potassium content were noticed, but, phosphorus and total protein content decreased. In addition, proline and total soluble sugar content increased; whereas, phosphorus, potassium, and total protein content declined at moderate to severe drought stress. Aphid infestation on mustard crops is negatively correlated to drought stress condition.