Occurrence of R-growth type of Tapesia yallundae fungus and its sensitivity to some fungicides

From winter wheat and winter triticale stems with distinct disease lesions 123 isolates of eyespot agent - <i>Tapesia yallundae</i> fungus were obtained. Stems were collected in 1999-2001, from no-treatment and protected with fungicides fields, which were situated in three provinces of Poland (małopolskie, mazowieckie, śląskie). Obtained isolates were classified on the basis of morphology on PDA, sporulation on water agar and sensitivity to carbendazim and prochloraz 51 isolates (i.e. 41,5% of all) represent R- growth type of fungus. To this type belong 28% and 71% strains obtained from wheat and triticale stems, respectively. Only seven isolates ofR-type fungus (i.e. 13,7%) were resistant to carbendazim. These strains originated from two protected with carbendazim winter wheat fields and two no-protected winter triticale crops. All isolates of R-type were sensitive to prochloraz. This compounds appears <i>in vitro</i> more effective than flusilazole, propiconazole and azoxystrobin.

The dominant pathogenic fungi on winter wheat in 1999-2001

The research works were carried out at the Agricultural Experimental Station of Agricultural University in Chylice, Mazowieckie voivodship. Diseases, their causal agents and occurrence on winter wheat cv. Kobra and cv. Mikon were studied in 1999-2001. Observations were performed in field conditions, on plots treated with fungicides and untreated control plots. Studies were concetrated on the most important pathogenic fungi occurring on winter wheat leaves, ears and stem bases, especiaIly <i>Puccinia recondita</i> on leaves (45% of infected leaf area), <i>Stagonospora nodorum</i> on ears (24% of infected ear area), <i>Mollisia (Tapesia) yallundae</i> (infection index 29) and <i>Fusarium</i> spp. (54% of infection culms) on stem bases. It has been proved that susceptibility to same diseases is strongly connected with cultivar and weather conditions. Average grain yield losses during three years period of study amounted: 1999 - 21,68%, 2000 - 7,34% and 2001 - 53,15% respectively.

Prediction of eyespot infection risks

The objective of the study was to design a prediction model for eyespot (<i>Tapesia yallundae</i>) infection based on climatic factors (temperature, precipitation, air humidity). Data from experiment years 1994-2002 were used to study correlations between the eyespot infection index and individual weather characteristics. The model of prediction was constructed using multiple regression when a separate parameter is assigned to each factor, i.e. the frequency of days with optimum temperatures, humidity, and precipitation. The correlation between relative air humidity and precipitation and the infection index is significant.

A New Source of Resistance to Tapesia yallundae Associated with a Homoeologous Group 4 Chromosome in Thinopyrum ponticum

Wheat (Thinopyrum ponticum line SS767; PI 611939) with 42 chromosomes previously was identified as a new source of eyespot resistance. Individual plants of SS767 were tested for reaction to Tapesia yallundae, the major pathogen of eyespot in the Pacific Northwest region of the United States. Resistance of this line was similar to the resistant winter wheat cv. Madsen (carrying gene Pch1 for eyespot resistance). Polymerase chain reaction analysis with primers specific for the J or E genomes revealed that SS767 contains Thinopyrum chromatin. Cytological and Cbanding analyses demonstrated that SS767 is a chromosome substitution line in which wheat chromosome 4D is replaced by a homoeologous group 4 chromosome of Thinopyrum ponticum. Genomic in situ hybridization using St genomic DNA from Pseudoroegneria strigosa as a probe, which can differentiate chromosomes from different genomes of Thinopyrum, indicated that this chromosome belongs to the J genome. Molecular analysis of an F2 population segregating for chromosome 4J and resistance to eyespot confirmed that eyespot resistance in line SS767 is associated with chromosome 4J of Thinopyrum ponticum. This is the first report of genetic control of resistance to eyespot derived from Thinopyrum ponticum. This source of resistance provides a new opportunity to improve wheat resistance to eyespot by adding to the diversity of resistance sources available.