SCREENING INDIGENOUS WHITE CLOVER POPULATIONS IN NORTHERN AREAS FOR BREEDING PURPOSES - A. Helgadottir^[19], A. Larsen^[20], P. Marum^[21], E. Lindvall^[22] and E. Miettinen^[23]

The use of white clover in sustainable farming systems in northern areas is hampered by the lack of productive, winter hardy varieties. In order to develop such varieties a total of 29 indigenous populations were evaluated for a number of agronomic characteristics under sward conditions at four locations across Iceland and northern Scandinavia for two consecutive years. The white clover cultivar Undrom from northern Sweden was used as a control. Seed characteristics were studied at two more southerly locations. For most of the agronomic characters and seed production characters such as seed yield, flowering date and head density, there were significant differences between populations but these were highly dependent on the test location. Some of the populations giving high forage yields were also among the highest seed yielders. Principal components analysis enabled us to identify populations that were superior for agronomic characters. Taking seed production characteristics into account it is possible to select promising populations for breeding.

INTRODUCTION

The use of white clover (Trifolium repens L.) in sustainable farming systems in northern areas is restricted by the lack of productive, winter hardy varieties. Commercial varieties of more southerly origin can be high yielding but generally lack the necessary winter hardiness. Indigenous material, on the other hand, is generally winter hardy, has small leaves, a prostrate growth habit and a low biomass production (Helgadottir, 1997). In order to breed varieties for the northern regions it may be necessary to combine the high biomass production of commercial varieties with the winter hardiness of superior, indigenous populations. The work described in this paper was designed to select superior populations on the basis of agronomic characteristics under sward conditions at a number of locations in the north. As commercial seed production is not a viable option in northern areas an evaluation of a number of seed production characteristics under more southerly conditions was also included.

MATERIALS AND METHODS

A total of 29 indigenous populations were screened in the study. These had been collected from various locations in Iceland and Scandinavia north of 62°N. The Swedish cultivar Undrom was used as a control.

For a comparison of agronomic characters 49 plants from each population were transplanted during the summer 1993 into a grass sward making up 1 m² plots in three replications at the Experimental Stations Korpa, Iceland (64°30'N), Holt, Norway (69°37'N), Sotkamo, Finland (64°40'N) and Robdacksdalen, Sweden (63°49'N). The material was planted out fairly late in the summer and the plots were not fully established until late in the following year. The populations were visually evaluated for a number of characters during two subsequent years. These included spring and autumn growth, amount of flowering, height, yield and vegetative spread three times during the growing season, and leaf size. Not all characters were evaluated at all locations and one location (Robacksdalen) only gave results for one year. The results were subjected to standard analyses of variance and principal components analyses were carried out for each location on variables that were common for all of them.

For the study of seed production characters, 25 spaced plants from each population were planted during summer 1994 into 1 m² plots, in three replications, at the Experimental Stations Svalov, Sweden (55°45'N) and Loken, Norway (61°08'N). The characters evaluated included date and synchronization of flowering, density and height of flower heads, date of maturity, seed yield, 1 000 seed wt., germination rate and proportion of hard seeds. More complete results were obtained from the Norwegian site.

RESULTS AND DISCUSSION

Significant differences between populations were observed for most of the morphological characters evaluated at each location and year. In addition, combined ANOVA over three locations for common characters at all sites showed significant interactions between populations and test sites for all characters. This means that the ranking of populations was highly dependent on the test site.

In order to elucidate the response patterns, results from three test sites, where data were available for two years, were subjected to principal components analysis. The following characters were used: spring growth, vegetative spread and yield evaluated twice during the growing season for both years and autumn growth for the first year (Figure 1 a-c). The first two axes accounted for over 80 percent of the total variation with the first axis accounting for 52, 67 and 61 percent at Korpa, Holt and Sotkamo, respectively. At both Korpa and Holt the measurements from the second year are a dominant factor on the first axis whereas the measurements from the first year dominate the second axis. At Sotkamo results from both years contribute equally to the first axis. Populations are selected at each location by mainly considering their position on the first axis in the principal components analysis as this axis contributes most to the total variation. This is further justified by the fact that the experimental plots were not properly established until the second year. As the main aim of the screening procedure was to identify populations which perform well at all locations a subset containing the better half of the populations was formed for each site and the intersection of these subsets contains the “best” populations. This is schematically presented in Figure 1 d. The outcome is further strengthened by the fact that three out of the four “best” populations were superior during the only year available at the fourth location.

Table 1. Seed production characteristics of selected populations and the control cultivar Undrom at Svalov (S) and Loken (L) compared with the overall mean for all populations included in the study.

Figure 1. Principal components analysis of results obtained at Holt (a), Korpa (b) and Sotkamo (c) and outcome of selection at each location (d). An open circle identifies selected populations and a number identifies populations superior at all sites (falling within the intersection of all three circles). Undrom (*) is the control cultivar.

The results from the seed production studies show (Table 1) that the selected populations gave adequate seed yields, density of flower heads and 1 000 seed wt. compared to the overall mean for all populations even though they did not surpass the control cultivar.

The present screening procedure has identified populations, which show superior performance at northern locations across Scandinavia. These are mainly characterized by higher biomass production and greater vegetative spread than their counterparts. They are therefore suitable for crossing with more southerly material in order to combine winter hardiness and good yielding ability.

ACKNOWLEDGEMENTS

This work was carried out with support from the Nordic Gene Bank. We acknowledge the assistance of technical staff at the different experimental stations. Trygve S. Aamlid carried out the seed quality studies and Thordis Anna Kristjansdottir assisted in the statistical analyses of the data.

REFERENCES

Helgadottir, A. 1997. Legume breeding in Iceland. Icelandic Agricultural Sciences 11, 29-40.