Yellow mosaic of mungbean and urdbean: current status and future strategies

The yellow mosaic disease (YMD) is known to affect a number of legumes in the country. However, mungbean and urdbean are the most important grain legume crops which are widely affected by this disease. Symptoms of the disease are broadly similar not only in mungbean and urdbean but also in other host plants and hence it is quite often taken as caused by the same virus. However, in the last decade rapid advancement has been made towards understanding of viruses involved in YMD. At present three distinct viruses viz., Mungbean yellow mosaic India virus (MYMIV), Mungbean yellow mosaic virus (MYMV) and Horsegram yellow mosaic virus (HgYMV) are known to cause YMD in mungnean and urdbean. Another common virus, Dolichos yellow mosaic virus (DoYMV) is known to cause YMD in Dolichos beans only. These four viruses along with some recently described begomoviruses from leguminous plant species are together termed as Legume Yellow Mosaic Viruses (LYMVs). Mungbean and urdbean also known as greengram and blackgram, respectively are important food grain legume crops (pulse crops) grown throughout India. These two legumes along with other legumes serve as an important source of protein to a large portion of the Indian population that traditionally practices vegetarianism. Mungbean and urdbean are primarily cultivated as Kharif (rainy season) crop, occupying about 25% of the total area under all pulse crops. With the development of short duration varieties, these crops have been successfully introduced as spring/summer crops in northern plains. In peninsular India, these crops are cultivated not only as Kharif crop but also as Rabi and summer crops. Introduction of these crops especially of urdbean in vast tract of rice fallows in many parts of south India and parts of Orissa is expected to increase contribution of these crops to the national pulse basket. In India mungbean occupied 3.38 million hectares in 2013–14 with a production of 1.61 m/t and a productivity of 474 kg/h. Urdbean occupied 3.06 m hectares with a total production of 1.70 million tonnes and a productivity of 535 kg/hectare. These two crops are known to be affected by yellow mosaic disease (YMD), the single most important biotic constraint to the production of these crops in the country. In this review article, progress made on various aspects of YMD in mungbean and urdbean including diagnostics for the causal viruses has been analyzed.