Latent Period (LP) was noted by Parlevliet and Van Ommeren (1975) as an indirect parameter for selecting for partial resistance (PR) to leaf rust (Puccinia hordei Otth). A correlation of (r= - 0.91) was found for LP and PR.
Several experiments were conducted in Mexico to find out if the same relationship existed for Yellow rust (P. striiformis Westend f. sp. hordei Eriksson). Latent Period was determined on sixteen resistant and susceptible cultivars to P. striiformis hordei race 24. The cultivars were sown in the greenhouse at El Batan Experiment Station located (2.200 meters elevation, 19o N latitude). The inoculation method was described by Broers and Lopez Atilano (1994). Latent period differences of thirteen days were found between the most susceptible cultivar Apizaco, and two resistant cultivars; Aleli, and Maris/Mink//ESC.II.72.83.3E.7E.5E.1E//Shyri.
The same cultivars were planted under field conditions at Toluca Experiment Station (2.600 meters elevation, 19o N latitude) to assess the Area Under Disease Progress Curve (AUDPC) using disease severity measured by using the severity part of the Cobb's modified scale. The Area Under Disease Progress Curve (AUDPC) for P. striiformis f. sp. hordei was small for resistant cultivars as compared to susceptible types (Table 1).
The results showed that Latent Period is a good indicator of partial resistance in some cultivars, but it is not a parameter that could be used universally in the identification of Partial Resistance. The highest correlation found for LP and AUDPC on three experiments was (r= -0.75). A selection based on LP alone, could have missed cultivars such as Calicuchima, with a relative intermediate LP and good levels of partial resistance as measured by the AUDPC.
A sister line of Calicuchima was studied extensively by P. Hayes
at Oregon State University. Two genes for resistance to yellow rust were
identified and mapped to chromosomes 4 and 7. The expresion of these genes
could explain the high levels of PR observed in Calicuchima in this study.
Table 1. Latent Period and Area under disease Progress Curve for yellow rust on six barley cultivars.
| Cultivar name | Laten period days | Area under disease progress curve1 |
| Maris Mink/ESC... | 26 | 120 |
| Aleli | 26 | 180 |
| Esmeralda | 23 | 1038 |
| Klages | 19 | 898 |
| Calicuchima | 19 | 66 |
| Apizaco | 13 | 2239 |
1 AUDPC measured on the flag leaf
References
Broers, L.H. and Lopez Atilano, R.M. 1994. A method of inoculating adult wheat plants with urediospores of Puccinia striiformis to measure components of resistance. Plant Dis. 78:353-357.
Chen, F.Q., Prehn, D., Hayes, P.D., Mulrooney, D., Corey, A.,and Vivar, H.E. 1994. Mapping genes for resistance to barley stripe rust
(Puccinia striiformis f. sp. hordei). Theor. Appl. Genet. 88:215-219.
Parlevliet, J.E. and Van Ommeren, A. 1975. Partial resistance of barley to leaf rust, Puccinia hordei. II. Relationship between field trials, micro plots test and latent period. Euphytica 24:293-303.
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