Yield improvement of oilseed rape (Brassica napus L.) in a low rainfall environment. II. Agronomic performance of lines selected on the basis of pre-anthesis development

Abstract

Agronomic characteristics of two groups of early flowering Brassica napus lines and their respective parents were compared at East Beverley in the Western Australian wheatbelt. These lines had been derived through two generations of backcrossing and subsequent selfing from crosses of the B. napus cultivar Wesbrook (recurrent parent) with an early flowering B. napus line RU2 and an even earlier flowering B. campestris population Chinoli C42. Lines selected for this experiment had flowered earliest in a previous controlled environment experiment. Only RU2 and one WesbrookxRU2 line (IB72) had significantly higher yields than Wesbrook (149% and 166% respectively), and one Wesbrookxchinoli C42 line was the only line to have a significantly lower yield than Wesbrook. None of the lines had significantly higher yields than their respective non-recurrent parents. Although RU2 and IB72 flowered much earlier than Wesbrook, there was no significant relationship between flowering time and seed yield over all lines. Lines which were the earliest to commence stem elongation tended to have higher seed yields. However, of all the growth and development characters measured, the biological yield and the dry weight increment between commencement of flowering and maturity were most closely related to seed yield. RU2 and IB72 accumulated far more dry matter over the post-anthesis period than Wesbrook and all other lines except another WesbrookxRU2 line. The superior post-anthesis growth of RU2 and IB72 may simply be a manifestation of the longer period available for growth under more favourable environmental conditions or deeper roots extracting more water from a greater depth. However, since there was no relationship between flowering time and the post-anthesis dry matter increment, it seems more likely that IB72 has received genes for superior post-anthesis growth as well as those determining early flowering from RU2. Given the rapid decline in soil moisture availability during post-anthesis development in this environment, these genes may affect post-anthesis growth through determining a greater capacity for drought avoidance. The implications of these results are discussed with particular reference to the breeding of higher yielding B. napus cultivars for lower rainfall environments.