Hung T. Ta1, Edmar I. Teixeira2, Derrick J. Moot1
1 Faculty of Agriculture and Life Sciences, Lincoln University, Lincoln 7647, New Zealand, PO Box 85804, http://www.lincoln.ac.nz/dryland, Derrick.Moot@lincoln.ac.nz
2 The New Zealand Institute for Plant and Food Research Ltd., Private Bag 4604, Christchurch, New Zealand
To understand the influence of fall dormancy ratings (FD) on lucerne, we measured growth (shoot elongation), vegetative (phyllochron) and reproductive (bud initiation) development during the establishment year of three contrasting genotypes grown with irrigation at Lincoln University, Canterbury, New Zealand. A dormant (FD2), a semi-dormant (FD5), and a winter-active (FD10) lucerne genotype were first harvested at the end of their seedling phase in January 2015 and then subjected to defoliations at 42-day intervals from summer 2015 to spring 2016. Leaf count at harvest was consistent among genotypes but differed seasonally, ranging from 7 to 15 leaves. The phyllochron was also similar among genotypes at 37 GDD per primary leaf for regrowth and 52 GDD for seedling lucerne. Branching rates were also similar for all genotypes and followed a seasonal pattern similar to leaf appearance rates. Stem height at the end of each regrowth cycle was greater for FD10 compared with FD5 and FD2. Regrowth lucerne required shorter thermal time of 416 GDD to reach 50% bud initiation compared with 613 GDD in seedling lucerne. In summary, plant height was the only morphological feature that differed among genotypes with contrasting fall dormancy ratings. In contrast, the phyllochron, branching rates and bud initiation were conservative but responsive to environmental signals.