Disease tolerance in a crop species may be defined as the ability of a plant to produce a greater yield than would normally be expected from the observed disease (Newton and Thomas, 1994). It is rarely a priority objective in breeding for resistance to fungal foliar diseases, particularly in cereals where there is considered to be a close association between observed disease and yield loss, especially under high input management.

Many data can be found from individual trials which indicate disease tolerance in cereals but these data are often inconsistent among trials indicating genotype by environment interaction in this character. The character can be quantified and whilst there is evidence for a heritable component of disease tolerance in spring barley to powdery mildew (Erysiphe graminis f.sp. hordei) (Newton and Thomas, 1994) its genetic basis is difficult to define.

We have developed methods for quantifying this character [1], determined that it is heritable in spring barley with respect to powdery mildew infection [2], and determined some of the factors which affect its expression [3].

Drought tolerance is a primary breeding objective in Mediterranean regions and is not unimportant as a yield-limiting factor even in temperate regions [4]. Furthermore, sudden drought-relief can result in temporary breakdown of resistance expression [5,6,7]. These are the subject of current research funded by an EU INCO grant, a BBSRC CASE studentship with the University of Oxford (Sarah Gurr) and a Scottish Government core-funded project.

Refereed publications

[1] Newton AC, Thomas WTB, 1994. Detection of tolerance of barley cultivars to infection by powdery mildew (Erysiphe graminis f.sp. hordei). Euphytica 75,179- 187.

[2] Newton AC, Thomas WTB, Guy DC, Gaunt R, 1998. The interaction of fertilisation with tolerance to powdery mildew in spring barley. Field Crops Research 55, 45-56.

[3] Newton AC, Guy DC, Gaunt RE, Thomas WTB, 2000. The effect of powdery mildew inoculum pressure and fertiliser level on disease tolerance in spring barley. Journal of Plant Diseases and Protection 107, 67-73.

[4] Forster BP, Ellis RP, Thomas WTB, Newton AC, Tuberosa R, This D, El-Enein RA, Bahri MH, Ben Salem M, 2000. The development and application of molecular markers for abiotic stress tolerance in barley. Journal of Experimental Botany, 51, 19-27.

[5] Newton AC, Young IM, 1996. Temporary partial breakdown of Mlo-resistance in spring barley by the sudden relief of soil water stress. Plant Pathology 45, 970-974.

[6] Baker SJ, Newton AC, Crabb D, Guy, DC, Jefferies RA, MacKerron DKL, Thomas WTB, Gurr SJ, 1998. Temporary partial breakdown of mlo-resistance in spring barley by sudden relief of soil water-stress under field conditions: the effects of genetic background and mlo allele. Plant Pathology 47, 401-410.

[7] Baker SJ, Newton AC, Gurr SJ, 1999. Cellular characteristics of temporary partial breakdown of mlo-resistance to powdery mildew in barley. Physiological and Molecular Plant Pathology (in press).

Non-refereed publications

[8] Thomas, WTB, Newton AC, 1993. Exploitation of tolerance to mildew in spring barley. Proceedings of the Crop Protection in Northern Britain Conference,1993, 121-126.

[9] Newton AC, Thomas WTB, 1993. Detection of tolerance to powdery mildew in spring barley. Sixth International Congress of Plant Pathology, Montreal,Abstract number 3.6.16

[11] Forster BP, Ellis RP, Newton AC, Tuberosa R, This D, El-Gamal AS, Bahri MH, Ben Salem M, 1999. Molecular markers for abiotic stress tolerance in barley. In: Molecular Physiology II: Engineering crops for hostile environments.