High-Temperature, Adult-Plant Resistance in the Barley Cultivar 'Bancroft' against Stripe Rust

Xianming Chen^1,2 and Mary Moore²

¹USDA-ARS and ²Dept of Plant Pathology, Washington State Univ., Pullman, WA

    Introduction Barley stripe rust, caused by Puccinia striiformis f. sp. hordei, is a relatively new disease in the United States. Since the disease was first reported in Texas in 1991, it has firmly established and caused substantial yield losses in Texas and the Western United States (Chen et al. 1995; Marshall and Sutton 1995). As the fungal pathogen has continued changing virulences, new races have been identified (Chen et al. 1995; Line and Chen 1999; Chen and Line 2001). The rapid changes of the pathogen virulence can circumvent race-specific resistance in barley cultivars.

    'Bancroft', developed by Dr. Wesenberg and his cooperators (Wesenberg et al. 2001), was one of the first barley cultivars developed in the US with resistance to stripe rust. It was formally released in February 2000. The cultivar had been highly resistant to stripe rust in North America until 2001 when the cultivar was observed moderately susceptible in Mexico (P. M. Hayes, personal communication, 2001). We added Bancroft in the set of barley cultivars that are used to differentiate races of P. striiformis f. sp. hordei in 2001. From the 2001 stripe rust samples in the US, we identified isolates from Texas, California, Oregon, and Washington that were virulent on seedlings of Bancroft. These isolates are to be designated as new races because they differ from previous races in the virulence on Bancroft (Chen and Moore, unpublished data).

    Even though we obtained stripe rust collections virulent on Bancroft from both western and eastern Washington, Bancroft remained resistant in the field nurseries in 2001. The objective of this study was to determine whether Bancroft has high-temperature, adult-plant (HTAP) resistance that has been well characterized in wheat and successfully used to control wheat stripe rust (Qayoum and Line 1985; Chen and Line 1995; Line and Chen 1995).

Materials and Methods

    Barley cultivars Bancroft and 'Steptoe' were used in this study. Steptoe, which is highly susceptible to all races of P. striiformis f. sp. hordei throughout the growth stages, was used as a control in this study. For the adult-plant test, four seeds of Bancroft and one seed of Steptoe were planted in each pot (6'' in diameter) filled with potting mixture of 24 L peat moss, 8 L perlite, 12 L sand, 12 L commercial potting soil, 16 L vermiculite, and 250 g 14-14-14 Osmacote. The arrangement of two cultivars in each pot was for easily comparing Bancroft with Steptoe through minimizing environmental variations. For the seedling test, Bancroft and Steptoe were planted in different pots of (3" X 3") filled with the potting mixture. Seeds for adult-plant tests were planted on February 6, 2002 and for seedling tests were planted on February 28. The plants were grown in a rust-free greenhouse before inoculation.

    When flag leaves of adult-plants were fully expanded and seedlings were in the two-leaf stage, the adult-plants and seedlings were inoculated at the same time with a mixture of talc powder (Sigma) and urediniospores of selected isolates of P. striiformis f. sp. hordeion March 13, 2002. The spores of the four isolates were increased on seedlings of Bancroft. Their origins and virulence patterns on the North American barley differentials are shown in Table 1. After inoculation, plants were placed in a dew chamber at 10o C for 24 h and then grown in the growth chambers at a low diurnal temperature cycle (gradually changed from 4^o C at 2:00am to 20^o C at 2:00pm) or a high diurnal temperature cycle (gradually changed from 10^o C at 2:00am to 35^oC at 2:00pm). A split-plot design was used for the experiment with two cultivars, two growth stages, and two temperature cycles with three replications.

Table 1. Isolates of Puccinia striiformis f. sp. hordei used in the tests, origins, and virulence and avirulence on the North America differential genotypes.

^a Urediniospores of the isolates were increased on seedlings of Bancroft (Ban).
^b Barley genotypes were used to differentiate races of P. striiformis f. sp. hordei: 1=Topper, 2=Heils Franken, 3=Emir, 4=Astrix, 5=Hiproly, 6=Varunda, 7=Abed Binder 12, 8=Trumpf, 9=Mazurka, 10=Bigo, 11=I 5, and 12=Bancroft.

    Infection type for each adult-plant or seedlings in each pot was recorded 23 days after inoculation based on the 0 - 9 scale (Line and Qayoum 1992). Infection types 0-3 were considered resistant, 4-6 intermediate, and 7-9 susceptible. The SAS program was used in analysis of variance to determine if the factors (cultivar, growth stage, temperature, isolates) had significant effects on the cultivar reactions to the stripe rust pathogen.

Results and Discussion

    Infection type means and standard deviations of Bancroft and Steptoe inoculated with four isolates of the pathogen at the seedling and adult-plant tests under the low and high-temperature cycles were shown in Table 2. When the data of Bancroft and Steptoe were analyzed jointly, a significant difference (P < 0.001) in infection type was detected between the two cultivars. Significant differences were also detected between the seedling and adult-plant stages and between the low and high temperatures (P < 0.001). Significant interactions were detected between cultivar and stage, cultivar and temperature, and stage and temperature. No significant difference was detected among tests with the four isolates (P = 0.20). The interaction of isolate with cultivar, stage, or temperature was not significant (P = 0.94, 0.28, and 0.17, respectively).

    When the two cultivars were analyzed separately, none of the factors (isolate, stage, and temperature) and the interactions between or among the factors was significantly different (P = 0.14 to 0.90). As expected, the results show that Steptoe is susceptible to all isolates tested at both seedling and adult-plant stages and at both low and high temperature cycles. In contrast, significant differences were detected with Bancroft between the tests at the two growth stages and at the two temperature cycles (P < 0.001). In addition, a significant interaction was detected between stage and temperature (P = 0.001). Tests with the four isolates were not significantly different (P = 0.46). As shown in Table 2, Bancroft had lower infection types when tested at the high-temperature cycle than when tested at the low-temperature cycle in both the seedling and adult-plant tests. Bancroft showed the highest resistance (lowest infection type) in the adult-plant test at the high-temperature cycle

    The results show that Bancroft has high-temperature, adult-plant (HTAP) resistance that has been well characterized in wheat for resistance to stripe rust (Qayoum and Line, 1985; Chen and Line 1995). The HTAP resistance in wheat has been demonstrated to be non-race specific and durable (Line and Chen 1995; Chen et al. 1998). In this study, the tests with four isolates from Texas, California, and Washington indicate that the HTAP resistance in Bancroft is non-race specific, and should be durable

    In this study, Bancroft had intermediate reaction in the adult-plant test at the low temperature cycle. The results agree with the observations that Bancroft was moderately susceptible in Bolivia and Mexico (Wesenberg et al. 2001; P. M. Hayes personal communication, 2001). In regions of a cool climate, Bancroft can be damaged by stripe rust, but the damage should be less than highly susceptible cultivars such as Steptoe. In regions like most of the Pacific Northwest of the United States, where HTAP resistance of wheat is highly effective in years with normal temperature during the growing season, Bancroft should have adequate resistance against stripe rust. Crosses of Bancroft with susceptible cultivars such as Steptoe are being made to genetically characterize the HTAP resistance, determine the relationship between the seedling resistance and the HTAP resistance, and to map genes conferring both types of resistance in Bancroft. The HTAP resistance in Bancroft should be useful in breeding programs for development of barley cultivars with durable and non-race specific resistance.

Table 2. Infection type means and standard deviations of Bancroft and Steptoe inoculated with isolates of Puccinia striiformis f. sp.hordei at the seedling and adult-plant stages under low and high post-inoculation temperatures

Literature cited

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