Quantitative trait loci for multiple disease resistance in wild barley

Foliar diseases of barley (Hordeum vulgare L.) such as spot blotch [caused by Cochliobolus sativus (Ito & Kuribayashi) Drechs. ex Dastur], net type net blotch (NTNB; caused by Pyrenophora teres f. teres Drechs), Septoria speckled leaf blotch (SSLB; caused by Septoria passerinii Sacc.), leaf scald [caused by Rhynchosporium secalis (Oudem.) J. J. Davis], and powdery mildew (caused by Blumeria graminis f. sp. hordei Em. Marchal) can result in significant yield reductions in many production areas. The wild progenitor of cultivated barley, Hordeum vulgare subsp. spontaneum is well known as a rich source of disease resistance. To determine the location of H. vulgare subsp, spontaneum-derived alleles for disease resistance, we conducted quantitative trait locus (QTL) analysis of a recombinant inbred line (RIL) population derived from a cross between the resistant H. vulgare subsp, spontaneum accession OUH602 and the two-rowed malting cultivar Harrington. A total of 151 simple sequence repeats (SSR) markers were mapped into 11 linkage groups, covering 948 cM. Major QTLs for resistance to each disease were identified: one for spot blotch resistance on chromosome 1(7H); three for NTNB resistance on chromosomes 3(3H), 4(4H), and 5(1H); two for SSLB resistance on chromosomes 2(2H) and 6(6H); one for leaf scald resistance on chromosome 5(1H); and two for powdery mildew resistance on chromosomes 4(4H) and 5(1H). Resistance alleles for each QTL were contributed by OUH602, except those for NTNB and powdery mildew resistance on chromosome 5(1H) and chromosome 4(4H), respectively. The two QTLs identified for SSLB resistance are novel. All other QTLs mapped to regions where known resistance QTLs or major resistance genes have been reported. Our results indicate that most of the OUH602-derived loci are clustered in regions coincident with those described in cultivated barley. These resistance QTLs and their associated markers should be valuable for further exploitation of disease resistance variation in barley improvement

Determination of aspartate kinase in maize tissues.

Lysine, threonine, methionine and isoleucine are synthesized from aspartate in a branched pathway in higher plants. Aspartate kinase plays a key role in the control of the aspartate pathway. The enzyme is very sensitive to manipulation and storage and the hydroxamate assay normally used to determine aspartate kinase activity has to be altered according to the plant species and tissue to be analyzed. We have optimized the assay for the determination of aspartate kinase in maize plants callus cell cultures. Among all the assay parameters tested, the concentration of ATP/Mg and temperature were critical for enzyme activity. In the case of temperature, 35°C was shown to be the optimum temperature for aspartate kinase activity