May 7, 2004
From: American Phytopathological Society, Plant Disease [edited]

Sterility mosaic disease - the "green plague" of pigeonpea: advances in understanding the etiology, transmission and control of a major virus disease
A. Teifion Jones, Scottish Crop Research Institute (SCRI), Scotland, UK; P. Lava Kumar, International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru, India, and SCRI; K. B. Saxena, ICRISAT; N.
K. Kulkarni, University of Agriculture Sciences (UAS), Bangalore, India, and ICRISAT; V. Muniyappa, University of Agriculture Sciences, Bangalore, India; and Farid Waliyar, ICRISAT. Plant Dis. D-2004-0308-01F.

Pigeonpea (_Cajanus cajan_), is a grain legume that is a very important subsistence crop in marginal farming systems adopted by millions of smallholder farmers in the Indian subcontinent. It is grown for its seed for human consumption and for income generation by trading surpluses in local and commercial markets, but is widely used for diverse purposes, including as animal fodder and for soil conservation.

Sterility mosaic (SMD) is the most damaging disease of pigeonpea endemic in the Indian subcontinent. It causes yield losses exceeding USD 300 million per annum in India and Nepal alone. SMD-affected plants show severe
stunting and mosaic symptoms on leaves, with complete or partial cessation of flowering. The SMD causal agent is spread by the arthropod mite vector _Aceria cajani_ (Aceria: Eriophyidae).

Cultivating SMD-resistant genotypes is the most viable way to manage this serious disease of pigeonpea. Progress in developing broad-based SMD-resistant material has been hindered by the lack of knowledge of the
causal agent, the absence of diagnostic tools, and factors influencing host-plant resistance.

After 7 decades of research, vital breakthroughs made on the identification, detection, transmission, and epidemiology of the SMD causal agent, Pigeonpea sterility mosaic virus (PPSMV), are enabling the development of broad-based durable resistant pigeonpea cultivars. These breakthroughs will contribute greatly to sustainable pigeonpea production and enhance the income and livelihood of poor farmers in the semi-arid tropics of the Indian subcontinent.

[Pigeonpea is grown on about 5.25 million ha, yielding 3 million tonnes, and contributes to about 5 percent of total world production of pulses. About 90 percent of global pigeonpea is grown in India and Nepal, and the remainder is cultivated in Africa, the Caribbean and Southeast Asia. There are no reports of SMD from Africa or the Americas. Infection by SMD in plants less than 45 days old results in 95-100 percent loss, while older plants suffer losses of 26-97 percent. SMD is the most significant disease of pigeonpea in India, causing losses over of USD 280 million in 1993.

A previously undescribed virus, Pigeonpea sterility mosaic (PPSMV), shows properties similar to viruses in the genus Tenuivirus. However, all tenuiviruses are phloem-limited, are transmitted by _Delphacid_ planthoppers and only infect species in the _Poaceae_, thus ruling out PPSMV as a tenuivirus. Ultrastructural studies of PPSMV-infected pigeonpea showed 100-150 nm quasi-spherical-membrane-bound bodies (MBBs) and fibrous inclusions (FIs). The filamentous VLPs of PPSMV resemble the nucleoprotein particles of Tomato spotted wilt virus (TSWV), and PPSV VLPs are slightly larger than those of TSWV. PPSMV shows no serological relationship to Maize stripe virus tenuivirus or Peanut bud necrosis tospovirus.

PPSMV and High plains virus share some common properties: transmission by the eriophyid mite _A. cajani_, 4-7 similar-sized MBBs and similar morphology. Similar MBBs have been detected in plants infected with fig mosaic, wheat spot mosaic, thistle mosaic and rose rosette, suggesting that these viruses may constitute a new virus genus.

Disease management of SMD will depend upon identification of broad-based resistant genotypes. These are relatively rare in the pigeonpea gene pool, but a related wild species, _C. scarabaeoides_ (Syn.: _C. indicus_) has
high levels of resistance to several pigeonpea biotic constraints. SMD thrives readily in crops under irrigation or near irrigated fields, and such crops are at risk of early infection.

A useful reference: <http://www.apsnet.org/pd/pdfs/2004/0308-01F.pdf> - Mod.DH]