Selection for resistance to salinity and waterlogging in Phalaris aquatica L.

Abstract

Dedication: This paper is dedicated to the memory of C. M. Donald, J. F. Miles, and C. A. Neal-Smith, who collected seeds of many Mediterranean populations of phalaris; these have been invaluable for breeding modern cultivars.

Because of the increasing area of southern Australia being threatened by rising saline groundwater, a search was made among 28 Mediterranean accessions and 10 Australasian cultivars of the deep-rooted, drought-resistant grass, phalaris (Phalaris aquatica L.), for genotypes that are more resistant to salinity and waterlogging than the present cultivars. In gravel medium watered with a nutrient solution containing 150 mol/m³ of NaCl and 10 mol/m³ of CaCl₂, a salt concentration equal to one-quarter strength seawater, the dry weight of live tops was reduced by an average of 58% relative to the non-saline treatment, whereas the reductions in the salt-tolerant control species, tall wheatgrass [Thinopyrum ponticum (Podp.) Z.-W. Liu & R.-C. Wang] and Aegilops tauschii Coss., were 13.4% and 26.6%, respectively. Sirolan was the highest yielding phalaris population under both saline and non-saline conditions, and Grasslands Maru and cv. Australian and its relatives were some of the least affected by salt. In a second experiment, the sodium content of the herbage of 1–3 cloned plants in each of 22 phalaris accessions averaged 1.62% in the treated offsets and 0.10% in the untreated offsets. Two genotypes in one accession, CPI 19315 from Morocco, had exceptionally low sodium concentrations and Na/K ratios in plants treated with salt. The means for these traits in CPI 19315 were 4.6 g/kg DM and 0.09, respectively, compared with means in the other 21 lines of 17.7 and 0.35.

CPI 19315 plants were crossed to seed-retaining, waterlogging-tolerant segregants from the backcross of P. aquatica × P. arundinacea to P. aquatica. The F₂ was compared with CPI 19315 and Grasslands Maru phalaris, Dundas tall wheatgrass, and AU Triumph tall fescue (Festuca arundinaceaSchreb.) on a winter-wet, saline discharge cline east of Wagga Wagga, NSW. Seedling density, emergence score, and dry matter yield at the end of the first growing season varied significantly among grasses and positions on the salinity/waterlogging gradient. However, the genotype and salinity effects on yield disappeared when seedling density was used as a covariate. Nevertheless, except for Dundas tall wheatgrass, herbage yield was correlated with position in the gradient, the F₂ and Dundas tall wheatgrass being less affected by increasing stress than Grasslands Maru, CPI 19315, and AU Triumph tall fescue.

Seed was harvested from putative seed-retaining F2 plants, and seedlings were transplanted into a saline discharge area near Canberra, ACT. The families differed significantly in injury and survival. The narrow-sense heritability of freedom from leaf injury was 0.52 0.28. Seed was again harvested from seed retaining survivors, and fourth generation seedlings were grown on the same area for continued selection. The plants in 3 family groups were significantly larger than of those in any of the control cultivar groups after 5 months exposure to waterlogging and salinity. Most survived the ensuing summer and autumn. The possibility of developing a cultivar better suited to saline, winter-wet, summer-dry soils is discussed.