First Report of Phakopsora pachyrhizi Causing Rust on Soybean in Malawi

Abstract

Soybean rust (SBR), caused by Phakopsora pachyrhizi, has become established in Africa since the first report in Uganda in 1996 (2). The urediniospores, as windborne propagules, have infested new regions of Africa, initiating SBR in many countries, including Ghana and Democratic Republic of the Congo in 2007 (4) and Tanzania in 2014 (3). No refereed reports have been published about rust in Malawi, but some people have indicated that soybean rust may have been observed as early as 2008. Typical symptoms and signs of SBR, including leaf yellowing and tan, sporulating uredinia, were observed on soybean in May 2014 during field surveys in the major soybean-growing areas of Malawi, including the central (Dowa, Mchinji, and Kasungu) and southern (Thyolo) regions in nine out of 12 sites surveyed. When microscopically examined, urediniospores were elliptical, echinulate, and hyaline to pale yellowish brown. Leaves exhibiting sporuliferous uredinia were sent by APHIS permit to the University of Illinois. To confirm the pathogen, symptomatic soybean leaf tissue of approximately 1 cm2 was excised from each of the samples, and DNA was extracted using the FastDNA Spin Kit (MP Biomedicals, Solon, OH), with further purification using the MicroElute DNA Clean-up Kit (Omega Bio-Tek, Norcross, GA). The resulting DNA was analyzed by quantitative PCR using published Taqman assays for P. pachyrhizi and P. meibomiae, with a multiplexed exogenous internal control reaction to validate negative results (1). P. pachyrhizi DNA was detected in excess of 180,000 genome equivalents/cm2 in all samples, indicating a substantial infection. P. meibomiae DNA was determined to be absent from all samples, within the limit of quantification of ~2 pg DNA/cm2. Urediniospores dislodged from three leaves and inoculated onto susceptible soybean cultivar Williams 82 produced tan lesions after 2 weeks of incubation in a detached-leaf assay. This is the first confirmed report of P. pachyrhizi causing rust on soybean in Malawi, putting at risk 14,000 ha currently under soybean production. The reports of soybean rust in Malawi and adjoining countries will alter soybean production practices and research interests. In some cases, foliar application of fungicides has increased and planting dates have been changed to avoid conditions that are most conducive for rust development. Efforts to understand the virulence and genetic diversity of the pathogen in the region are needed in order to develop and deploy resistant cultivars. References: (1) J. S. Haudenshield and G. L. Hartman. Plant Dis. 95:343, 2011. (2) R. Kawuki, et al. Afr. Crop Sci. J. 11:301, 2003. (3) H. M. Murithi et al. Plant Dis. 98:1586, 2014. (4) P. S. Ojiambo et al. Plant Dis. 91:1204, 2007.

Soybean production in eastern and southern Africa and threat of yield loss due to soybean rust caused byPhakopsora pachyrhizi

“…Within the same period (1998), the disease was reported in the major soybean growing regions in Kenya, Rwanda, Zimbabwe (Jarvie, ) and Zambia (Levy, ), in Nigeria in 1999 (Akinsanmi et al ., ), in Mozambique in 2000, in South Africa in 2001 (Pretorius et al ., ) and in Cameroon in 2003 (Levy, ). Other reports of the disease on soybean followed in 2007 in Ghana and the Democratic Republic of Congo in central Africa (Bandyopadhyay et al ., ; Ojiambo et al ., ), and recently in Tanzania and Malawi (Murithi et al ., , ; Fig. ).…”

Diversity and distribution of pathotypes of the soybean rust fungusPhakopsora pachyrhiziin East Africa

“…The fungus produces numerous urediniospores that are easily dispersed over short (Wen et al, 2017) and long (Isard et al, 2007) distances by wind currents, leading to new infections. Soybean rust was first observed in Africa in 1996 (Kawuki et al, 2003) and has so far spread to more than 10 countries in the continent (Murithi et al, 2015). Losses from soybean rust infection range from 10% to 80% worldwide (Levy, 2005), raising concerns about its impact on the rapidly growing soybean sector in Africa.…”

Evaluation of soybean genotypes for resistance against the rust‐causing fungus Phakopsora pachyrhizi in East Africa

“…The fungus spread rapidly and was reported after its introduction into Uganda on soybean in South Africa in 2001 (Pretorius et al, 2001), in western Cameroon in 2003 (Levy, 2005), and in Ghana and the Democratic Republic of Congo in 2007 (Bandyopadhyay et al, 2007;Ojiambo et al, 2007). The disease was also confirmed in Ethiopia, Malawi, and Tanzania (Murithi et al, 2014(Murithi et al, , 2015Tesfaye et al, 2017). A second species causing rust on soybean, Phakopsora meibomiae, has not been reported in Africa or elsewhere outside the Americas (Hartman et al, 2011).…”