Legume yellow mosaic virus: Pulses play a very significant role in the nutritional safety of a large number of people across the world.
They signify as main source of protein in many developing countries, particularly among the poorer section of the population who chiefly depend on vegetable sources for the requirement of their protein and energy.
These are chiefly consumed as proteins source in Pakistan. Pulses cultivation covers an area of 5% worldwide. Their consumption varies as a protein source. These are mainly consumed for their proteins as food of babies to rich and poor.
Among major pulses, gram is cultivated as major winter while moong is grown as Kharif legume. In Punjab, gram cultivation covered an area of 956.4 thousand ha while mungbean is cultivated over an area 206.6 thousand ha with their yearly production is 760.6 thousand tons and 118 thousand tons, respectively.
While their annual production revealed the area and production which is 87-88% in case of chickpea and 91-92% for mungbean. In Pakistan, the causal agent of yellow mosaic disease is yellow mosaic virus (YMV).
Its dissemination occurred by vector whitefly (Bemisia tabaci). This yellow mosaic disease of legumes is menace to mungbean production in Pakistan, Sri-Lanka, Papu New Guinea, Bangladesh, Thialand, India, and Philippines.
Whitefly (Bemisia tabaci)
Whiteflies or snow flies are the tiny, sap-sucking insects of plants. They are related to other sap sucking insects such as aphids, mealybugs and able to fly when plant get disturbed. Bemisia tabaci belongs to order “Hemiptera”.
Whiteflies completes its lifecycle within three weeks under suitable conditions. Whitflies are the vector of legume yellow mosaic viruses and cause severe damage to crop by transmiting the virus.
Legume yellow mosaic viruses are the members of family geminivridae and genus begomovirus. Begomoviruses universally known as geminiviruses. These geminate viruses belongs to family Geminiviridae and genus begomovirus the most noteworthy viruses in the Geminiviridae.
These plant viruses consist of single stranded circular DNA (ssDNA) genome and categorized by their geminate particles. Begomoviruses are registered as monopartite with single DNA and bipartite viruses having DNA-A and DNA-B components. Begomoviruses are economically most important genus in this family that preferably infects dicots and only transmit by their natural vectors.
Begomoviruses chiefly infects dicots especially soybean, mungbean and urdbean due to their genomic body. There genome is 2.8kb in size. Geminivirus infection expressions mostly appeared as leaf curling, mosaic, vein yellowing and leaf yellowing. Four species of bipartite begomoviruses (family Geminiviridae) are the cause of YMD of legumes in southern Asia till date.
In many nucleus related tasks, DNA-A component of bipartite is involved. It translates all important factors that are essential for viral DNA replication for example it codes the replication associated protein (Rep), rolling-circle replication-initiator protein and DNA helicase and the replication enhancer protein (REn), the transcriptional activator protein (TrAP) and encapsidation/insect transmission the coat protein (CP).
Both components of bipartite viruses share a common sequence region consist of 200 nucleotides named as common region (CR). The DNA-A component has one gene (AV1) on the viral sense strand and three other genes named as AC1, AC2, and AC3 on the corresponding strand for the New World (NW) bipartite Gemini-virus and further a gene AV2 in the viral sense strand and C4 on the corresponding strand for the Old World (OW) bipartite begomoviruses.
The DNA-B component of bipartites translates two genes. These genes are the nuclear shuttle protein (NSP) and the movement protein (MP). These two genes worked collectively and play important role in the virus dissemination from one cell to other cells and build a systemic infection in plants. In detailed inquiries on the gene expression, revealed that MYMV have shown the binding of the transcription products in geminiviruses for the first time.
Genomic organization of begomoviruses