Effect of Diseases on Soybean Yield in the Top Eight Producing Countries in 2006

By A. Wrather, G. Shannon, R. Balardin, L. Carregal, R. Escobar, G. Gupta, Z. Ma, W. Morel, D. Ploper, A. Tenuta. 2010

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The objective of this project was to compile estimates of yield loss in soybean [Glycine max (L.) Merr] to diseases in the top eight soybean-producing countries in 2006. The purpose was to provide information needed by local and world agencies to allocate funds for research and to help scientists focus and coordinate research efforts. Methods used by plant pathologists to estimate yield loss to diseases in these countries included systematic field surveys, cultivar trials, diagnostic clinic records, personal observations, and questionnaires sent to crop consultants and extension staff. The 2006 harvest of soybeans in the top eight soybean-producing countries was reduced an estimated 59.9 million metric tonnes (t) by diseases according to results of the current study. Soybean rust, caused by Phakopsora pachyrhizi, reduced yield in all these countries except Canada in 2006, and the total was more than any other. Next in decreasing order of total yield loss were soybean cyst nematode, brown spot, seedling diseases, anthracnose, and charcoal rot. Introduction The total soybean production for the world during 2006 was 220.4 million t (5). The top eight soybean-producing countries were the U.S. (83.4 million t), Brazil (57.0 million t), Argentina (40.5 million t), China (16.4 million t), India (7.0 million t), Paraguay (3.6 million t), Canada (3.16 million t), and Bolivia (2.0 million t). These countries produced about 97% of the world supply for 2006. High yields are critical to soybean producer profit margins, even during periods when soybean prices are high. Unfortunately, yields in major soybean producing countries have been suppressed by diseases in the past (6), and income derived from this crop has been less than optimal. This financial loss is important to rural economies and to economies of allied industries. Research must focus on management of diseases that cause extensive losses, especially when funds are limited. The objective of this project was to compile estimates of soybean yield losses to diseases in the top eight soybean-producing countries for the 2006 harvested crop. The goal was to show the extent of yield loss to help local and world agencies allocate funds for research and to help scientists focus and coordinate research efforts. 25 January 2010 Plant Health Progress Estimates of Yield Loss Due to Diseases Methods used by plant pathologists to estimate yield losses to diseases in these countries were based on systematic field surveys, cultivar trials, diagnostic clinic records, personal observations, and questionnaires sent to crop consultants and extension staff (6). Most of the individuals used several of these methods and consulted with their colleagues to develop their estimates. Losses in the United States were compiled from estimates submitted by plant pathologists in each state. Yield losses were based on estimates of yield in the absence of disease. Estimates for each country were specific for the causal organism or the common name of the disease as listed by Hartman et al. (1). Effects of Environment and Production Practices Soybean in most regions of these eight countries is grown under conditions that favor the survival of pathogens and development of disease. Soybean yield losses to diseases varied due to weather in most countries. Charcoal rot was most severe in the dry areas of Argentina, Bolivia, Brazil, India, Paraguay, and the United States. Cool, wet weather at planting enhanced seedling disease in the United States and Canada. Wet weather at bloom stage enhanced Sclerotinia stem rot in the United States and Canada, enhanced Rhizoctonia aerial blight in India, and enhanced anthracnose in the central and northern portions of Brazil and Paraguay. Wet weather at harvest enhanced Phomopsis seed decay in Canada. The severity of rust was related to the frequency of rain in Argentina, Bolivia, Brazil, China, India, Paraguay, and the United States. Factors that have contributed to the escalation of disease problems in these countries include planting poor quality seed, increased monocropping of soybean, and increased use of crop management practices such as no-tillage which favor pathogen survival and the increase of inoculum. Phomopsis seed decay was more severe in early-maturing cultivars planted earlier than normal in the United States and Argentina, but Sclerotinia stem rot was less severe in Argentina due to this practice. Rust was more severe on late than early planted soybean in Paraguay due to more favorable weather for it late in the growing season. Most soybean diseases were managed by resistant cultivars and fungicides. Because the use of these resources remains incomplete and limited to only certain diseases, soybean production continues to suffer losses to diseases. Soybean yield losses to rust have been reduced very little by planting resistant and tolerant cultivars in China and parts of South America because the resistance has not been durable. Yield losses to this disease have been reduced by application of fungicides to soybean foliage in China, Argentina, Bolivia, Brazil, and Paraguay. The effects of fungicides on rust incidence and severity in the United States vary among fungicides and time of application (4). Argentina. Nearly 80% of soybean production in Argentina was from the central and Pampean region (provinces of Buenos Aires, Córdoba, La Pampa, San Luis, and Santa Fe), 9.5% was from the northwestern region (provinces of Catamarca, Jujuy, Salta, Santiago del Estero, and Tucumán), and 10.5% was from the eastern region (provinces of Corrientes, Chaco, Entre Ríos, Formosa, and Misiones). The number and severity of infectious diseases have increased steadily, particularly since the early 1990s (3). Yields for the soybean crop harvested in 2006 were suppressed by several diseases (Table 1). Seedling diseases caused by various pathogens such as Fusarium spp., Pythium spp., Rhizoctonia solani, and Phytophthora sojae were only important in early plantings in the central and Pampean region. 25 January 2010 Plant Health Progress Table 1. Estimated reduction of soybean yields (thousand metric tonnes) due to diseases in the top eight soybean-producing countries in 2006. w Tr = trace. x Other nematodes were lance, lesion and reniform in Brazil; primarily lesion as well as lance, sting, and stubby root in Canada; and lance, lesion, reniform, sting and stubby root in the United States. y Virus diseases were soybean mosaic, alfalfa mosaic, peanut mottle, tobacco streak, cucumber mosaic and bean common mosaic in Argentina; cucumber mosaic in Bolivia; mungbean yellow mosaic, soybean mosaic and peanut bud necrosis in India; and soybean mosaic, bean pod mottle, tobacco ringspot and peanut mottle in the United States. z Other diseases were target spot in Argentina and Bolivia, Rhizoctonia root rot in Canada, grey spot in China, and Myrothecium leaf spot and target spot in India. Disease Argen -tina Bolivia Brazil Canada China India Paraguay USA Total Anthracnose 45.3 Trw 220.0

Subfields: Molecular Biology

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