QTL analysis for flowering time using backcross population between Oryza sativa Nipponbare and O. rufipogon

Abstract

In the near future, global average temperature is expected to increase due to the accumulation of greenhouse gases, and increased temperatures will cause severe sterility in many crop species. In rice, since wild species show high genetic variation, they may have the potential to improve the flowering characters of cultivars. In this study, we investigated flowering characters under natural conditions by comparing an Asian wild rice accession of Oryza rufipogon W630 (originated from Myanmar) with a Japanese rice cultivar, O. sativa Japonica cv. Nipponbare. Further, QTL analysis for days to heading (DH) and spikelet opening time (SOT: the time of day when the spikelet opens) was carried out using BC(2)F(8) backcross population derived from the cross between them. Regarding DH, four QTLs were detected, and two of them were found to have wild alleles with strong effects leading to longer days to heading during the Japanese summer. These wild alleles may be used to produce late-heading cultivars that do not flower during the high summer temperatures anticipated in the future. As for SOT, two parameters of SOTb (beginning time when the first spikelet opens) and SOTm (median time when 50% of the spikelets open) were recorded and the time differences from Nipponbare were investigated. Two QTLs on chromosomes 5 and 10 and two QTLs on chromosomes 4 and 5 were detected for SOTb and SOTm, respectively. The wild alleles were responsible for early spikelet opening time at all loci. If the wild alleles detected in this study have the same effects in the genetic background of other cultivars, they will be very useful in producing early-flowering rice cultivars that complete fertilization in the morning before the temperature rises.

Breeding efforts to mitigate damage by heat stress to spikelet sterility and grain quality

“…Two wild rice accessions have been used to map the QTL for EMF. Thanh et al (2010) made the first attempt using the mapping population of nipponbare/O.…”

“…Japanese cultivars, Hatsuboshi (Iida et al, 2002;Wakamatsu et al, 2007) and Hinohikari (Wakamatsu et al, 2007(Wakamatsu et al, , 2008, are known as susceptible cultivars, while Hana-echizen (Kobayashi et al, 2007), Koshijiwase (Iida et al, 2002;Tabata et al, 2007), Fusaotome (Tanaka et al, 2010;Wakamatsu et al, 2008), Kokoromachi (Shirasawa et al, 2013), Chikushi52 , and Genkitsukushi rufipogon. Three QTLs for EMF were detected on chromosomes 4, 5, and 10, indicating that the alleles of O. rufipogon shifted FoT to 30 min earlier than nipponbare (Thanh et al, 2010). Another attempt was made by Hirabayashi et al (2015), using O. officinalis as a donor parent.…”

PHENOTYPIC AND GENOTYPIC ANALYSIS FOR EARLY MORNING FLOWERING TRAITS AT FLOWERING STAGE IN RICE (Oryza sativa L.)

“…Peak flowering in this study was considered when 50% of the spikelets were opened (Thanh et al 2010). …”

“…These microsatellite markers can be possibly linked or associated to the start of flower opening time for the EMF trait in rice. Similarly, Thanh et al (2010) using backcross population, identified QTL for starting time when the first spikelet opened (SOTb) on chromosome 5, with markers flanking RM249-RM440. These results indicate that chromosomes 5, 7, 8, 9, and 11 were most likely the possible QTL locations for peak flowering time, time when most of the flowers are closed and time when all of the flowers are closed.…”

“…These results indicate that chromosomes 5, 7, 8, 9, and 11 were most likely the possible QTL locations for peak flowering time, time when most of the flowers are closed and time when all of the flowers are closed. Thanh et al (2010) reported that related QTL was detected for peak flowering time on chromosome 5 in the region of RM249. In this study, the QTL region for SOTb and peak flowering time on chromosome 5 overlapped which could indicate the most likely location of flower opening time QTL in rice.…”