Heritability of response to moisture stress in a New Zealand North Island hill country ryegrass collection grown with and without nitrogen fertiliser

Abstract

The heritability of ryegrass plant response to moisture stress and nonstressed conditions under nil and 3.5 kg nitrogen (N)/week was measured. 39 parent plants (6 clones/parent) and progeny seedlings (6 × 3/parent) were grown in a simulated hill soil profile at 5 cm spacing. One half of the soil bin received 3.5 kg N/week and the other half zero N. A single harvest and tiller count was taken in December. Water was withheld for 85 days, the bin flooded, and dry weight and tiller counts were noted. A second bin was planted with parents and progeny of plants selected for morphological traits. Added N increased tiller number and plant dry weight in the pre-drought measurement with a smaller effect on post-drought measurements. There was a strong phenotypic correlation between tiller number and dry weight post-drought measurement. Seedling-derived offspring were more vigorous than the clonally propagated parental generation. The results indicate significant genetic effects on the ability of ryegrass plants to recover from moisture stress. Estimates of the heritabilities of plant dry weight and tiller number before and after drought ranged from 0.2 to 0.6 on a single plant basis when estimated from parent-offspring regressions. Estimates of genetic correlations between tiller number and pre- and post- drought dry weights were moderate to very high and suggest that tiller number may be a useful concomitant or indirect selection criterion for improving drought tolerance. The estimated heritabilities for heading date and leaf length and width were lower than those reported elsewhere.