Indirect Selection for Root Development of White Clover and Implications for Drought Tolerance

Abstract

Improving white clover drought tolerance by selecting for more developed roots is controversial, labour‐consuming and complicated by the adventitious root system. This study aimed at assessing: (i) the value of thicker stolons as an indirect selection criterion for increasing root development, (ii) the relationship between root development and drought tolerance, and (iii) the consistency of population response for root and shoot traits between swards derived from seedlings or stolon cuttings. Thick‐ and thin‐stolon populations obtained by one cycle of divergent phenotypic selection within one ladino landrace, and one ladino natural population, were evaluated in metal containers (0.55 m × 0.12 m × 0.75 m deep) in a 1‐year experiment including vegetative material (seedling or stolon cutting) and drought stress (absent or present) as additional factors. Aerial dry weight (DW) was also assessed across two summer harvests under irrigated and rainfed field conditions for the thick‐stolon selection, two breeding populations selected from the same landrace regardless of stolon thickness, and the drought‐tolerant ladino ‘Brown Loam Synthetic no. 2’. The thick‐stolon selection had greater root DW (+21 %) than the thin‐stolon selection besides thicker stolons (+23 %). The natural population combined thinnest stolons with lowest root DW. Differences between populations were consistent across vegetative material. Primary and adventitious root systems did not differ for root DW in deeper soil horizons (>23 cm), above‐ground biomass and its reduction due to drought stress. Root DW increased under stress, particularly in deeper horizons. Aerial DW variation among populations evened up or narrowed much under stress, with no cross‐over interaction leading to an advantage of thick‐stolon material or ‘Brown‐Loam Synthetic no. 2’.

Rooting depth and root depth distribution ofTrifolium repens×T. unifloruminterspecific hybrids

“…Babu et al (2003) also reported positive correlations between quantitative trait loci for root traits and rice yield under drought. In contrast, Annicchiarico and Piano (2004) found no correlation between root traits and drought tolerance in white clover, but suggested this was due to its poor physiological adaptation to water stress. Improved physiological tolerance of T. repens  T. uniflorum BC 1 hybrids (Nichols et al, 2015a) may enable the beneficial effects of root characteristics on drought resistance to be expressed.…”

“…Improved physiological tolerance of T. repens  T. uniflorum BC 1 hybrids (Nichols et al, 2015a) may enable the beneficial effects of root characteristics on drought resistance to be expressed. Annicchiarico and Piano (2004) also speculated on the possible importance of fibrous roots in white clover during drought, and it seems likely that both fine roots and thicker, deeply penetrating roots play a role in drought resistance. It is worth noting that a combination of fine and thick roots may be particularly important in the presence of multiple soil limiting factors, such as drought and low soil fertility.…”

Achievements and Challenges in Improving Temperate Perennial Forage Legumes

“…Assessment of divergent selections in the field showed increased root:shoot ratio, root diameter and root numbers all be associated with increased yield in moisture-limited and well-watered conditions (Caradus and Woodfield, 1998). Indirect selection for stolon root development based on stolon diameter increased root dry matter, although this did not led to improved drought tolerance in the test conditions (Annicchiarico and Piano, 2004).…”

Características morfofisiológicas associadas à tolerância à seca em sete genótipos da coleção nuclear de trevo branco

“…Os autores sugeriram ainda que outras características observadas nos genótipos tolerantes como, por exemplo, o pequeno tamanho de folha, deve atuar junto com o aumento da concentração de pinitol, conferindo essa vantagem adaptativa em lugares secos. ANNICCHIARICO & PIANO (2004) conduziram um estudo a fim de verificar se a densidade de estolão pode ser usada como um critério de seleção indireta para melhorar o desenvolvimento de raiz do trevo branco tipo ladino e os resultados mostraram uma relação positiva entre densidade de estolão e desenvolvimento de raízes. Entretanto, os autores afirmaram não existir nenhuma evidência de uma relação positiva entre desenvolvimento de raiz e tolerância à seca, visto que a massa seca de raízes aumentou quando sob estresse, particularmente em solo de horizonte profundo.…”