Effect of summer moisture deficit on growth of five white clover cultivars

Abstract

Growth of five New Zealand white clover cultivars, Grasslands Kopu, Grasslands Pitau, Grasslands Huia, Grasslands Tahora and Prop, was quantified at differing soil moistures in both the field and the glasshouse. The first trial employed a rain-out shelter to impose two soil water treatments. While there were no differences among the cultivars for leaf water status, there were differences in plant growth parameters in response to water deficit. Water deficit did not significantly affect leaf appearance rate of Prop, although there was a 2- fold difference. There was, however, a 3.5- to 6-fold decrease in leaf appearance rate due to water deficit for the other cultivars. Water deficit did not significantly reduce leaf size for the medium- and small-leaved cultivars Huia, Tahora and Prop; but was halved for Kopu and Pitau. Prop had the lowest stolon growing point survival under water deficit and Pitau the highest. Leaf longevity was greatest for Prop and least for Pitau when grown under optimum water supply, but this pattern was reversed under water deficit stress. The second trial, a pot trial, investigated the response of the same five cultivars to three different soil water regimes (control, mild and severe stress). The growth parameters of smaller-leaved cultivars, particularly Prop, were less affected than the large-leaved cultivars in their response to water deficit. These short-term trials showed that some small-leaved cultivars of white clover have an ability to adjust their growth and habit in response to water deficit more effectively than large-leaved cultivars. Prop was able to maintain a higher leaf appearance rate than other cultivars when grown under water deficit. However, while exhibiting this drought tolerance adaptation the low stolon growing point survival of Prop could result in a poor recovery from drought. Small-leaved cultivars are rarely taprooted, a characteristic of plants adapted to more prolonged drought conditions. The probability of combining these characteristics and improving summer production of white clover through identification of drought tolerance is discussed. Keywords: cultivars, drought, Trifolium repens, variation, water deficit