TABLE CONTENTS

Resistance to Rotylenchulus reniformis in Cotton (Gossypium hirsutum)
Davis, R.F. (1) & A.F. Robinson (2)
(1) USDA-ARS, Tifton, GA 31794, USA; (2) USDA-ARS, College Station, TX 77845, USA
The reniform nematode (Rotylenchulus reniformis) is a major problem in cotton (Gossypium
hirsutum) production and resistant cultivars are lacking. The development of cotton cultivars
with resistance to reniform nematode appears possible but presents a significant research
challenge, primarily for two reasons. First, the best sources of resistance occur within diploid
species that are genetically incompatible with upland cotton. Second, without molecular
markers, reniform nematode resistance can only be detected by lengthy nematode
reproduction assays. Thus, it is absolutely essential to discover a molecular marker for each
resistance source to provide seed companies with a tool for monitoring inheritance of
resistance as they proceed through the cultivar development process. Simultaneous
introgression of resistance from sources within several species is the wisest approach,
because incomplete expression or incorporation of closely linked deleterious genes is
possible in all cases, and in each case an investment of many years is required before success
can be gauged by field testing of elite resistant breeding lines at multiple sites. Currently,
researchers at more than a dozen USDA laboratories and state-supported universities in the
United States have projects targeting introgression of reniform nematode resistance into
agronomic upland cotton, from primitive tetraploid accessions of Gossypium hirsutum and G.
barbadense, and diploid G. arboreum and G. longicalyx. This task will take many years to
complete. However, significant progress has been made toward developing cultivars carrying
resistance from each source, and the first resistant cultivars could appear within 3 years, with
committed follow through by commercial planting seed companies.
Marker Assisted Transfer of Cereal Cyst Nematode Resistance from Bread
Wheat into Durum Wheat
Ogbonnaya, F.C.(1,2), J. Jahier (3) & E.S. Lagudah (4)
(1) DPI, PB 260, Horsham Victoria 3401, Australia; (2) ICARDA, PO Box 5466, Aleppo, Syria;
(3) INRA Station d'Amelioration des Plantes, BP 29, 35653 Le Rheu cedex, France; (4) CSIRO Plant Industry,
GPO Box 1600, Canberra ACT 2601, Australia.
Cereal cyst nematode (CCN) (Heterodera avenea Woll.) is a damaging disease of bread
wheat, Triticum aestivum L. and durum wheat, T. turgidum L.. Breeding for the host-plant
resistance is the most economically effective means of controlling the disease. The objective
of this study was to transfer CCN resistance gene, Cre1 from hexaploid to tetraploid durum
wheat, so that Cre1 can be used directly for the improvement of durum wheat. NB-LRR gene
sequences from the Cre3 locus were previously shown to identify homologues that were
diagnostic for bread wheats carrying the Cre1 gene. Molecular probes diagnostic for Cre1
based on the Cre3-derived sequences were used to select tetraploid wheat derivatives from
BC 1 F 2 progenies of breadwheat x durum wheat cultivars while Dgas44, which is diagnostic
for the presence of D genome was also used to select against progenies carrying D genome.
Selected BC 1 F 3 tetraploids with and without the Cre1 diagnostic probe were then examined
in a CCN bioassay in France and Australia for the levels of nematode reproduction. The
results revealed successful transfer of CCN resistance gene, Cre1, from bread wheat to four
durum wheat cultivars - Arstar, Cham1, Creso and Villemur and confirmed perfect
association between the diagnostic marker and Cre1 resistance in the tetraploid
5 th International Congress of Nematology, 2008 14