Managing flowering time inMiscanthusand sugarcane to facilitate intra- and intergeneric crosses

Abstract

Miscanthus is a close relative of Saccharum and a potentially valuable genetic resource for improving sugarcane. Differences in flowering time within and between Miscanthus and Saccharum hinders intra- and interspecific hybridizations. A series of greenhouse experiments were conducted over three years to determine how to synchronize flowering time of Saccharum and Miscanthus genotypes. We found that day length was an important factor influencing when Miscanthus and Saccharum flowered. Sugarcane could be induced to flower in a central Illinois greenhouse using supplemental lighting to reduce the rate at which days shortened during the autumn and winter to 1 min d-1, which allowed us to synchronize the flowering of some sugarcane genotypes with Miscanthus genotypes primarily from low latitudes. In a complementary growth chamber experiment, we evaluated 33 Miscanthus genotypes, including 28 M. sinensis, 2 M. floridulus, and 3 M. ×giganteus collected from 20.9° S to 44.9° N for response to three day lengths (10 h, 12.5 h, and 15 h). High latitude-adapted M. sinensis flowered mainly under 15 h days, but unexpectedly, short days resulted in short, stocky plants that did not flower; in some cases, flag leaves developed under short days but heading did not occur. In contrast, for M. sinensis and M. floridulus from low latitudes, shorter day lengths typically resulted in earlier flowering, and for some low latitude genotypes, 15 h days resulted in no flowering. However, the highest ratio of reproductive shoots to total number of culms was typically observed for 12.5 h or 15 h days. Latitude of origin was significantly associated with culm length, and the shorter the days, the stronger the relationship. Nearly all entries achieved maximal culm length under the 15 h treatment, but the nearer to the equator an accession originated, the less of a difference in culm length between the short-day treatments and the 15 h day treatment. Under short days, short culms for high-latitude accessions was achieved by different physiological mechanisms for M. sinensis genetic groups from the mainland in comparison to those from Japan; for mainland accessions, the mechanism was reduced internode length, whereas for Japanese accessions the phyllochron under short days was greater than under long days. Thus, for M. sinensis, short days typically hastened floral induction, consistent with the expectations for a facultative short-day plant. However, for high latitude accessions of M. sinensis, days less than 12.5 h also signaled that plants should prepare for winter by producing many short culms with limited elongation and development; moreover, this response was also epistatic to flowering. Thus, to flower M. sinensis that originates from high latitudes synchronously with sugarcane, the former needs day lengths >12.5 h (perhaps as high as 15 h), whereas that the latter needs day lengths <12.5 h.

Characterization of the Ghd8 Flowering Time Gene in a Mini-Core Collection of Miscanthus sinensis

“…Dong et al [ 7 ] observed that short days (<12.5 h) were also a signal for M. sinensis from high latitude plants to induce a short-internode dormancy response, which is an adaptation to protect apical meristems from damaging low temperatures during winter in high latitudes, and this dormancy response was epistatic to flowering. Similar dormancy responses to short days have been found in several quantitative short-day, perennial, C4 grasses, including M. sacchariflorus [ 4 ], switchgrass ( Panicum virgatum ) [ 64 ] and big bluestem ( Andropogon gerardii) [ 65 ].…”

“…The M. sinensis accessions represent six genetic groups that were previously identified by Clark et al [ 49 , 50 ]. Dong et al [ 7 ] previously evaluated the same twelve accessions for days to first flowering under day lengths of 15, 12.5 and 10 h in controlled environment chambers, and observed strong flowering time responses that varied by latitude of origin. In the current study, six pots of each accession were established by planting rhizomes in 2 L plastic pots containing soilless medium consisting of compost, vermiculite, calcined clay and peat moss (Forex Mori Sangyo Co., Ltd., Hokkaido, Japan) and growing these in a greenhouse at Hokkaido University in Sapporo, Japan (43.1° N, 141.3° E), with natural photoperiod.…”

“…For Miscanthus production, optimization of flowering time is essential to obtain high biomass yield under different environments [ 4 , 5 ], and may also impact biomass quality [ 6 ]. Controlling flowering also assists intra- and interspecific hybridizations between Miscanthus and Saccharum to facilitate the introgression of genes for disease resistance and abiotic stress tolerance from Miscanthus to sugarcane [ 7 ]. Additionally, to develop seed-based hybrid cultivars of Miscanthus , uniform flowering of the parental genotypes will be needed, and this has the potential to reduce the cost of establishment and accelerate domestication relative to the current standard approach of vegetatively propagating rhizomes of Miscanthus× giganteus , which is a hybrid between M .…”

“…Initially, M. sinensis was described as a day neutral plant by Deuter [ 11 ], whereas Jensen et al [ 8 ] demonstrated that flowering regulation in M. sinensis was complex, operated by thermal time/degree days but also a photoperiod sensitivity mechanism. In their latest study, Dong et al [ 7 ] reported that M. sinensis was a facultative short-day (SD) plant, and photoperiod strongly affected Miscanthus flowering. Thus, it would be desirable to study the photoperiod regulation of flowering time in M. sinensis .…”

“…To date, information on the genetics of flowering regulation in Miscanthus is in its infancy [ 4 , 7 , 8 ]. Genetic linkage maps revealed fourteen flowering time quantitative trait loci (QTLs) in Miscanthus [ 29 , 30 , 31 ].…”