Responses of a New Zealand North Island hill perennial ryegrass collection to nitrogen, moisture stress, and grass grub (Costelytra zealandica) infestation

Publisher Website
Google Scholar
Abstract
A hill country perennial ryegrass collection from 60 sites throughout the North Island hill country in New Zealand was screened for tolerance of three important stresses in hill country: low nitrogen (N), moisture stress, and grass grub infestation. The screening was carried out in a simulated hill soil profile using 1800 hill plants (30 plants from 60 sites), four standard cultivars, and two local ecotypes each represented by 30 individuals. Plants were subjected to: (1) 0 versus 7 kg N/ha per week; (2) no water for 12 weeks versus regular watering; and (3) the addition of 600 grass grub larvae/m2. When grown with added N, plants removed from steep slopes i.e., conditions of severe N deficiency, produced less dry matter than plants removed from less stressed environments. Plants removed from northern steep slopes i.e., subjected to seasonal severe moisture stress, had a low yield compared with plants removed from wetter areas when grown with a regular water supply. Plant N concentration was similar across a wide range of plants. Screening for tolerance to grass grub was inconclusive. Ellett ryegrass had a higher yield under each stress than the other standard cultivars. The morphological measurements of individual plants were regressed against their response to stress but no significant correlations were observed. Three types of hill plants were identified: (1) plants removed from stressed environments demonstrating stress tolerance but unable to produce as well on relief of stress as those plants removed from less stressed environments; (2) plants which produce well under optimum conditions but not under stress; and (3) plants in the top 10% of producers under both stress and unstressed conditions. The implications for plant breeding programmes are noted.