Sources of Resistance to Downy Mildew in Wild and Weedy Sorghums

Abstract

Sorghum downy mildew (SDM), caused by Peronosclerospora sorghi Weston and Uppal (Shaw), is a serious disease of sorghum [Sorghum bicolor (L.) Moench] and maize (Zea mays L.). The wild relatives of sorghum, both cross compatible and cross incompatible with S. bicolor, could provide alternate sources of resistance genes for the long‐term control of SDM. The objective of this study was to assess the downy mildew reaction of several taxa of wild and weedy sorghums. One hundred three wild and weedy sorghums, and six cultivated types belonging to five sections, representing 17 species, originating from Asia, Australia, Africa, and the USA, were greenhouse tested for downy mildew resistance during the rainy seasons of 1998 and 1999 at ICRISAT, Patancheru, India. Forty‐five accessions comprising 15 species from four sections, parasorghum, heterosorghum (S. laxiflorum Bailey), chaetosorghum (S. macrospermum Garber), and stiposorghum (S. angustum S. T. Blake, S. ecarinatum Lazarides, S. extans Lazarides, S. intrans F. Muell. ex Benth., S. interjectum Lazarides, S. stipoideum (Ewart & Jean White) C. Gardener & C. E. Hubb.), including all accessions from Australia, exhibited immunity to downy mildew. Cultivated types and wild races of section Sorghum showed the greatest susceptibility (mean downy mildew infection of 62 and 46%, respectively), while accessions of S. halepense (L.) Pers. were comparatively less susceptible (36% mean downy mildew infection). Potential new sources of resistance genes from wild and weedy sorghums were identified that could be used to develop resistant cultivars to control downy mildew.

Genetic structure and relationships within and between cultivated and wild sorghum (Sorghum bicolor (L.) Moench) in Kenya as revealed by microsatellite markers

“…The high genetic diversity could potentially be exploited in broadening the genetic base of sorghum breeding germplasm, while the unique diversity imply that wild sorghum is a potential source of novel genes such as pests and disease resistance. The genetic potential of wild relatives of sorghum, particularly as sources of resistance to pests and diseases, is well documented such as for sorghum shoot fly (Kamala et al 2009), sorghum midge (Sharma and Franzmann 2001), green bug (Duncan et al 1991), downy mildew (Kamala et al 2002) and ergot (Reed et al 2002). Moreover, the substantial genetic variability and differentiation revealed in sorghum landraces of Kenya should be incorporated in breeding programs by developing different populations with a broad genetic base.…”

“…Wild relatives of sorghum are recognised as broad genetic base reservoirs and potential sources for resistance and adaptation traits in breeding programs (Gurney et al 2002;Kamala et al 2002;Reed et al 2002;Rao Kameswara et al 2003;Rich et al 2004) and deserve special conservation attention.…”

Ecogeographical distribution of wild, weedy and cultivated Sorghum bicolor (L.) Moench in Kenya: implications for conservation and crop-to-wild gene flow

“…The potential of wild sorghum to provide new sources of resistance and adaptation in breeding programs have been established (Sharma and Franzmann 2001;Gurney et al 2002;Kamala et al 2002;Rao Kameswara et al 2003) but only partially explored. Conversely, crop-to-wild gene flow could result in the spread of genes from both domesticated and transgenic varieties into wild populations, and possible subsequent creation of aggressive weeds or invasive plants (Ellstrand et al 1999;Conner et al 2003), depending on the characteristics of the introgressed genes.…”

Utilization of wild relatives for maize (Zea mays L.) improvement

“…Wild crop relatives have been playing enormously important roles both in the depiction of plant genomes and the genetic improvement of their cultivated (Brar, 2005;Hajjar and Hodgkin, 2007;Pickering et al, 2006;Canci and Toker, 2009;Miller and Seiler, 2003). They have contributed immensely to resolving several fundamental questions, particularly those related to the origin, evolution, phylogenetic relationship, cytological status and inheritance of genes of an array of crop plants; provided several desirable donor genes for the genetic improvement of their domesticated counterparts; and facilitated the innovation of many novel concepts and technologies while working on them directly or while using their resources (Bai et al, 1995;Clifford, 1995;Kamala et al, 2002;Nevo et al, 2002 ;Nevo, 2004;Raskina et al, 2002Raskina et al, , 2004Sharma et al, 2005;Price et al, 2005Price et al, , 2006Dillon et al, 2005Dillon et al, , 2007Peleg et al, 2005Peleg et al, , 2007Petersen et., 2006;Salina et al, 2006;Matsuoka and Takumi, 2007;Bennetzen et al, 2007;Gill et al, 2007;Feldman and Kislev, 2007;Oliver et al, 2008;Loskutov, 2008;Gavrilova et al, 2008;Kuhlman et al, 2008;Xu et al, 2009;Wang et al, 2009;Ashraf et al, 2009;Nevo and Chen, 2010;Chittaranjan, 2011). For example, a wild rice (Oryza officinalis) has recently been used to change the time of flowering of the rice cultivar Koshihikari (Oryza sativa) to avoid the hottest part...…”