Fusarium head blight (FHB) of wheat was considered a sporadic disease in Uruguay until 1976; however, due to favorable weather conditions in the spring of 1977, the first of many epidemics ocurred. Disease samples collected around the country during 1990-92 showed Fusarium graminearum to the most prevalent species causing FHB. During 1991-93, studies carried out to identify genetic variability in the fungus showed differential responses in aggressiveness with respect to the isolates' reaction on the host. However, no host pathogen interaction was observed. To further analyze this variability, work was conducted in collaboration with the John Innes Institute, UK, using random amplified polymorphism DNA (RAPD) and restriction fragment length polymorphism (RFLP). Although certain differences in the intensity of the band were observed among different isolates, these belonged to the same general pattern; hence, in this case, RFL markers were not successful in identifying polymorphisms within F. graminearum. At present, research is underway to identify superior FHB resistant germplasm under field conditions, using artificial inoculation. in general, Chinese sources of resistance, though agronomically poor, have performed well. CIMMYT germplasm derived from crosses with Chinese germplasm show superior levels of FHB resistance in high yielding plant types. Of these, a Catbird selection (CM91045-5Y-0M-OY-4M-0Y-0B) has been selected for its stable FHB resistance under field and greenhouse conditions, and is being crossed with local germplasm. In order to transfer high levels of resistance to locally adapted types, inoculum density and timing of inoculations have been found to be of critical importance. A large CIMMYT collection evaluated for FHB during 1994 demostrated significant differences in the infection level on advanced lines with the same day of flowering. It was also observed that the highest level of natural infection took place during a very short period of time, whereas outside this period, The level of infection was generally lower, even on moderately susceptible to susceptible germplasm. Therefore, in order to avoid escapes under natural infection conditions, resistance in germplasm must be identified during the peak infection period. Since all Uruguayan wheat cultivars are susceptible to FHB at present, diversification of sowing date and/or chemical control are recommended. Experimental data show that two applications of Benomyl, Prochlora, or Tebuconazol at stage 61 and 65 (Zadoks' scale) achieve better results than a single application at either stage 61 or 65.

English

R97-98PROCE|9806|AGRIS 9802|R97PROCE|anterior|AR96-97E|FINAL9798

Jose Juan Caballero

CIMMYT Publications Collection