Evaluating temperate species in the subtropics. 3. Irrigated lucerne

Abstract

Performance of lucerne cultivars and breeding lines, when grown under irrigation in the Queensland subtropics in individual experiments and when averaged over the 25 years from 1981 to 2006, is presented. In the overall analyses, only cultivars which were entered in at least 2 experiments were included. Entries were evaluated in small plot cutting experiments over 3-year periods. Seasonal, annual and total dry matter yields were recorded, along with field disease assessments and persistence. Highest seasonal, annual and total (60-64 t/ ha) yields were produced by highly winter-active cultivars (activity levels 8 and 9) with little differences between Sequel, Sequel HR, Hallmark, Sceptre, Aquarius and Pioneer L90, although yields of a number of Queensland-bred cultivars with lower activity levels (<8) were not significantly lower. Individual experiments were more discriminating, with the Queensland-bred cultivars Sequel and Trifecta producing the highest (P<0.05) or equal to the highest yields in 8 of 10 and 9 of 14 experiments in which they were included, respectively. Other high-yielding cultivars included Aquarius, Aurora, Genesis, Hallmark, Pioneer L55, Sceptre and UQL-1. Average winter yields ranged from 1.7 t/ha for Hunter River to 3.2 t/ha for Hallmark, while the range in individual experiments was larger (1.1-5.7 t/ ha), taking into account the range from dormant to highly active material. Disease played a significant role in defining production levels until the drought years of 2001-2006, when the effects of Colletotrichum crown rot (CCR), phytophthora root rot (PRR) and the leaf disease complex of Stemphylium vesicarum and Leptosphaerulina trifolii were reduced. Trifecta was consistently in the group of cultivars showing most resistance to these diseases, while Hunter River showed equal or better resistance to Colletotrichum crown rot and the leaf disease complex. On average, only 12 - 20% of the original populations survived until the end of the third year, with Hallmark, Trifecta and Sequel consistently the most persistent cultivars. There was a wide range in persistence between experiments (general mean of 29% in 1984 compared with 5% in 1995), with environmental conditions appearing to play as important a role as disease resistance. The best performing cultivars under subtropical conditions were winter-active (7 and 8) or highly winter-active (9 and 9+) ones, that had either been specifically bred for the region or undergone screening for disease resistance, particularly for CCR and PRR, which are recognised as a problem in the region. Cultivars with lower winter activity levels were generally loweryielding, even though in some instances they showed good persistence.