Genetic control of flowering in spotted gum, Corymbia citriodora subsp. variegata and C. maculata

Abstract

Abstract. Genetically controlled asynchrony in anthesis is an effective barrier to gene flow between planted and native forests. We investigated the degree of genetically controlled variation in the timing of key floral developmental stages in a major plantation species in subtropical Australia, Corymbia citriodora subsp. variegata K.D. Hill and L.A.S Johnson, and its relative C. maculata K.D. Hill and L.A.S. Johnson. Flowering observations were made in a common garden planting at Bonalbo in northern New South Wales in spring on 1855 trees from eight regions over three consecutive years, and monthly on a subset of 208 trees for 12 months. Peak anthesis time was stable over years and observations from translocated trees tended to be congruent with the observations in native stands, suggesting strong genetic control of anthesis time. A cluster of early flowering provenances was identified from the north-east of the Great Dividing Range. The recognition of a distinct flowering race from this region accorded well with earlier evidence of adaptive differentiation of populations from this region and geographically-structured genetic groupings in C. citriodora subsp. variegata. The early flowering northern race was more fecund, probably associated with its disease tolerance and greater vigour. Bud abundance fluctuated extensively at the regional level across 3 years suggesting bud abundance was more environmentally labile than timing of anthesis. Overall the level of flowering in the planted stand (age 12 years) was low (8-12% of assessed trees with open flowers), and was far lower than in nearby native stands. Low levels of flowering and asynchrony in peak anthesis between flowering races of C. citriodora subsp. variegata may partially mitigate a high likelihood of gene flow where the northern race is planted in the south of the species range neighbouring native stands.

Flowering phenology in a Eucalyptus loxophleba seed orchard, heritability and genetic correlation with biomass production and cineole: breeding strategy implications

“…There was however, no trend in northern provenances to flower earlier than the more southerly E grat provenances, a trend recorded for E. marginata 63 and for Corymbia citriodora subsp. variegata and C. maculata 27 . However, the opposite trend has been observed in E. globulus where Victorian provenances flowered later than the more southerly eastern-coast Tasmanian provenances 26 .…”

“…due to asynchrony in flowering time) may lead to unbalanced contributions of genetic material from individual parents to the next generation and reproductive isolation 23 . Several studies have shown that time of anthesis in eucalyptus is under genetic control, resulting in different flowering times between provenances and families 24 – 27 . Therefore, understanding the reproductive phenology of a seed orchard can enable culling reproductively isolated trees, families or provenances thereby increasing the overall level of outcrossing in the orchard.…”

Variety is the spice of life: Flying-foxes exploit a variety of native and exotic food plants in an urban landscape mosaic

“…Urban landscapes are often warmer than surrounding natural areas (Magee et al, 1999), and are maintained by human intervention, and thus can have increased soil moisture and soil nutrient loads (Sukopp, 2004;Neil and Wu, 2006). These factors have been hypothesized to promote more regular and intense flowering for plants, including locally indigenous Australian natives, within urban landscapes (e.g., Davis et al, 2016), although given the key role of photoperiod in regulating plant reproduction (Jackson and Thomas, 1999;Jarillo et al, 2008;Abasolo et al, 2014) it is unlikely that the season of flowering would change even if conditions were favorable. Thus, while urban landscape characteristics may promote more reliable flowering and extended food availability of locally indigenous plant species, it is unlikely that these locally indigenous species alone could support P. poliocephalus in Adelaide year-round.…”