Monday, November 13, 2006

Identification of Resistance Mechanisms to Striga hermonthica in Maize.

Idris Amusan1, Patrick Rich2, Abebe Menkir3, Thomas Housley2, and Gebisa Ejeta4. (1) Purdue Univ, Dept of Agronomy, 915 W State St, 1150 Lilly Hall, West Lafayette, IN 47907-2054, (2) Purdue Univ, Dept. of Agronomy, 915 W. State St, West Lafayette, IN 47907-2054, (3) Carolyn House 26 Dingwall Road, International Institute of Tropical Agriculture - IITA, International Institute of Tropical Agriculture, c/o L. W. Lambourn & Co., Croydon, CR93EE, ENGLAND, (4) Purdue University-Agronomy Dept., Purdue Univ.-Dept. of Agronomy, 915 W. State St. 1150 Lilly Hall, West Lafayette, IN 47907-2054

Breeding for resistance to Striga in maize, with paucity of donor sources with defined mechanisms of resistance can be challenging without an efficient selection method. In this study, we developed a new bioassay that allows non-destructive sampling and progressive observation of resistance reactions during the post-attachment phase of   parasitic development. A new  bioassay, sand filled plexi glass assay (SFPGA), was developed to evaluate post attachment development of Striga on a field tested putative source of resistance (Z.Diplo.BC4-19-4-1-#-3-1-B-1-B-B) and a susceptible (5057) maize inbred obtained from the maize breeding program of  IITA. In addition, haustorial invasion of Striga hermonthica into roots of susceptible and resistant maize inbred lines were examined histologically.The resistant maize inbred had fewer Striga attachments, delayed parasitic development, and higher mortality of attached parasites compared to the susceptible inbred, 5057. Morphological and physiological differences were observed between roots samples of susceptible and resistant maize lines under light microscopy. The Striga resistant genotype exhibited failure of Striga haustoria to penetrate beyond the endodermis as well as haustorial collapse and tylosis-like occulations in the xylem vessel. These results suggest that the resistant inbred (Z.Diplo.BC4-19-4-1-#-3-1-B-1-B-B) may have an incompatible response type resistance with some physiological barrier to Striga parasitism. The assay was useful in identifying specific mechanisms of the resistance deployed. To our knowledge, this is the first report of  post-attachment resistance mechanisms to Striga in cultivated maize.