3.1.23
HYBRID WHEAT DISEASE RESISTANCE AND FUNGICIDE RESPONSE

RE BEALE1, G BLACHE1, J-M BERNET1 and G GRUWEZ2

1HybriTech, Centre de Recherche de Morenval, 60350 Cuise Ia Molle, France; 2HybriTech, Centre de Production de Sevestreville, 28140 Orgeres en Beauce, France

Background and objectives
Over recent years, hybrid wheat varieties have gained an increasing proportion of the French wheat area. The success of these varieties has been their high yield potential, being as much as 16% greater than inbred varieties [1]. More recent hybrid introductions, such as Cockpit, have coupled bread-making quality with high yield. Linked with the introduction of hybrid wheat have been publications of studies on their agronomic performance [1, 2], yet specific data relating to their disease resistance or the modification of fungicide inputs are lacking. The current paper reports results from artificially inoculated screening trials examining hybrids and inbred breeding material, and naturally infected fungicide trials with commercial or near-commercial hybrids and inbreds.

Materials and methods
Inoculated field screening of hybrid wheat varieties and inbred breeding lines was conducted at the Morenval and Sevestreville sites in 1997 using inoculum of Tapesia yallundae (eyespot), Septoria tritici (septoria leaf blotch), Stagonospora nodorum (septoria leaf and ear blotch) and Fusarium culmorum (fusarium head blight). Inoculum was produced in bulk quantities under laboratory conditions on cereal grains and agar substrates. Each pathogen was used to inoculate a separate experiment containing single-row field plots 1 m in length for each hybrid or inbred line. Mist-irrigation systems manipulated climatic conditions in favour of epidemic development. In separate experiments at the same locations, four hybrids and two inbreds were compared under differing fungicide programmes for disease resistance under naturally infected situations. Fungicide programmes consisted of different combinations of Unix (cyprodinil) at GS30, Opus Team (epoxiconazole & fenpropimorph) at GS39 and Caramba (metconazole) at GS 59. For all experiments, disease assessments were made on several occasions during epidemic development and maturity.

Results and conclusions
High levels of disease were recorded in each of the inoculated field trials. Several of the new hybrids, such as Cockpit and Cebestan, demonstrated good all-round resistance. Cockpit was particularly resistant to T. yallundae , F. culmorum, S. tritici and S. nodorum. Cabestan also showed high fusarium resistance with medium eyespot and septoria resistance. Comparisons with inbred parents of these and other hybrids showed that resistance levels were usually similar to one or other of the two parents. However, in the hybrids Cabestan, HYB 95B and HYB 96E, resistance to fusarium appeared to be better than that of the parents, and in the case of HYB 96E this was also true for eyespot resistance. This may indicate an advantage of heterosis for polygenic inherited diseases. Results from naturally infected trials confirmed the resistance of Cockpit to eyespot, with disease indices in untreated plots not differing from those in the cyprodinil-treated plots. The performance of Cockpit and Cabestan against septoria was also found to be superior to the hybrid Domino and other inbred wheat varieties.

Data from these studies demonstrate the value of new hybrid wheat varieties for disease resistance and suggest their suitability for integration in a low-input fungicide system.

References
1. Bodson B, Franc J, Destain J-P, et al., 1997. Aspects of Applied Biology 50, 23-30.
2. Angus WJ, 1997. Aspects of Applied Biology 50, 15-22.