Abstract

A comparison was made of the growth on acid and non-acid soils near Canberra of 66 lines in Phalaris aquatica, in seven other Phalaris species which can be crossed with P. aquatica and in seven allopolyploid or backcross hybrids involving P. aquatica. The yield of tops by mid-spring on the strongly acid site was only 20% of that on the mildly acid site. Some variation was apparent among the 38 P. aquatica accessions and cultivars, but some P. arundinacea accessions and hybrids were less inhibited by acidity than any P. aquatica line. Fifty plants from the first or second backcross of four P. aquatica X P. arundinacea hybrids to P. aquatica were selected for their capability of producing a large root system in a nutrient solution containing 10 mg aluminium per L at pH 4.1. On acid soils near Bendigo, Seymour, Benalla and Canberra, offsets of seven of these backcross plants were rated as growing significantly larger at the end of the first growing season than plants of Sirosa, Sirolan and Uneta phalaris, Porto and Currie cocksfoot, Demeter and Melik tall fescue and of Victorian and Brumby perennial ryegrass. However, two of the backcross genotypes appeared to be significantly smaller than the phalaris and cocksfoot controls. Thus, factors in addition to excess aluminium appear to affect the growth of phalaris in these soils, but some backcross genotypes tolerate these adverse conditions. Four of the productive, acid-tolerant genotypes survived the first summer, regenerated vigorously in the following autumn, were palatable to sheep in test grazings over two summers at Armidale, N.S.W., and also were fertile and retained some of the ripe seed in their panicles. Therefore, it seems probable that phalaris cultivars for acid soils in south-eastern Australia can be selected from later generations of the backcross population.