Genetic control of adaptive root characteristics in white clover

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Comparison of 11 white clover genotypes revealed a 3-fold variation in taproot diameter and proportion of fibrous roots to total root dry weight varied from 0.45 to 1.00. Shoot type, determined by leaf size, was positively correlated with taproot diameter and number of vertically penetrating roots (r = 0.86 and 0.95, respectively, P < 0.001, df = 9), but negatively correlated with proportion of fibrous to total root dry weight (r = −0.87, P < 0.001, df = 9). Three cycles of selection for taproot diameter were carried out in one population, with a response to selection of 2.4% per cycle. Divergent selection for taproot diameter and for root weight ratio (proportion root weight to total plant weight) was done in two different populations. The impact of the divergent taproot and root weight ratio selections on performance was assessed under grazing in a drought-prone environment and in a controlled-environment study, respectively. Selection for medium leaf size and large taproot diameter gave yields 70% better in moist conditions and 35% better under dry conditions than that of the standard cultivar, Grasslands Huia. Selection for increased root weight ratio was also effective in improving growth and survival in drought prone environments. Selection for specific root characteristics has improved yield and persistence in drought prone environments.

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