Yellow rust of barley is an invasive disease that was found in the past 10 years in North America. The causal agent, Puccinia striiformis f. sp. hordei, was introduced into Colombia, South America, from Europe in 1975. It spread to all major barley-producing areas in South America by 1982. In 1988 it was found in Mexico and in 1991 in Texas. Since then it has been found in all major barley-producing areas of the American West. Originally described as race (R) 24, barley yellow rust in North America is now known to be a very heterogeneous population. Resistance has been identified, evaluated, and is being introduced into commercial malting and other barley cultivars. Cultural and chemical controls are effective and available. An integrated approach using general field resistance and other tactics is described for sustainable management of barley yellow rust.

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Fusarium acuminatum is one of the causal agents of dryland root rot of winter wheat in Colorado. The effect of F. acuminatum seedling root infection, recorded at heading, on winter wheat cultivars Sandy and CO84 was investigated in the greenhouse. Winter wheat seeds were surface disinfested, germinated, and vernalized. Vernalized seedling roots were inoculated by placing a single, germinated macroconidium of F. acuminatum on the largest root. Inoculated and non-inoculated vernalized seedlings were transplanted to pots and half the plants subjected to water stress. Inoculated plants had significantly lower survival rates and, at maturity, lower relative leaf water content, fewer tillers, shorter plant height, and higher cell ion leakage than non-inoculated plants. Wheat cultivars differed significantly for most traits studied. CO84 was susceptible whereas Sandy was more tolerant of the pathogen, particularly under water stress conditions. These results suggest that relative leaf water content, cell ion leakage, and to some extent seedling survival may be useful attributes for evaluation of resistance to the root rot pathogen.

Sets of 24 ascospores were isolated from crosses between seven isolates of the number of effective factors controlling these two parasitic fitness Helminthosporium maydis race T. Conidial suspensions of ascospore attributes. The effective factor estimates from the 24 ascospore analyses cultures were used to inoculate quantitatively seedlings of two corn hybrids ranged from 2.8 to 6.7 for DE and from 4.0 to 7.5 for SC. Pooled estimates (RX404 and PA887 X B14) in Texas male-sterile cytoplasm. Disease ranged from 5.8 to 7.9 and from 15.8 to 25.4 for DE and SC, respectively. efficiency (DE, the average number of lesions per plant) and sporulation These results, along with the relatively high heritabilities of DE (21-58%) capacity (SC, the average number of conidia produced per square and SC (23-52%), suggest that these parasitic fitness attributes could millimeter of lesion) were measured and analyzed. The genotypic variance respond to selection. The utilization of "nonspecific" resistance may was calculated and used along with the progeny extreme values to estimate provide selection pressure toward increased parasitic fitness.