An evaluation of wild populations of perennial ryegrass from dairy farms in the Waikato and Bay of Plenty districts

Abstract

A ryegrass breeding programme to improve the seasonal growth and plant persistence of perennial and hybrid ryegrasses in the Waikato began at AgResearch Ruakura, Hamilton in 2001. One approach was to characterise the genetic diversity of the naturalised populations within 26 dairy farms from different districts around the Waikato and Bay of Plenty (BOP) regions. Plants from 26 individual breeding lines were evaluated as single spaced plants over a 3-year period in comparison with three commercialised ryegrass cultivars. Principal Component Analysis was used to order the plant populations in accordance with the observed plant variables of seasonal growth pattern, tillering ability, leaf size and extension, and the incidence of crown rust. A hierarchical cluster analysis of the wild populations revealed two distinct plant groups. A mix of large leaf Italian Lolium multiflorum and hybrid plants were typical from the warmer drier areas of the BOP. The Italian ryegrass was prone to severe crown rust infection whereas the hybrids were more resistant. Shorter, narrow leaved and densely tillered plants with a high rust infection dominated the Waikato populations. Ecotypes that maintained high plant tiller density throughout the seasons had the best persistence. Plants that displayed an improvement in seasonal yield and tillering over the commercial cultivars were considered an important genetic source to develop new persistent cultivars for the Waikato and BOP regions. Keywords crown rust, drought, ecotypes, Lolium spp., plant breeding