Accurate Evaluation of Photoperiodic Sensitivity and Genetic Diversity in Common Buckwheat under a Controlled Environment

Abstract

Photoperiodic sensitivity is one of the most important factors determining whether a crop can adapt to and be cultivated under a broad range of conditions. In common buckwheat (Fagopyrum esculentum Moench), flowering time (flowering of the first flower) is a complex trait influenced by photoperiod, light quality, and temperature, which change daily under natural conditions, and their interaction. Common buckwheat shows a large genetic variation because of the outcrossing reproductive strategy of this species. Thus, flowering time variation within a population reflects both environmental and genotypic variations, and accurate evaluation of photoperiodic sensitivity in common buckwheat requires cultivation under controlled environmental conditions. Here, we investigated photoperiodic sensitivity and its genetic diversity in two buckwheat cultivars, the autumn ecotype Miyazakizairai and the summer ecotype Botansoba, by controlling photoperiod during cultivation under the same temperature regime. Our results showed that (1) the summer ecotype consisted of early-flowering genotypes, including genotypes not found in the autumn ecotype; (2) the autumn ecotype consisted of various genotypes, including early-flowering genotypes and a large number of late-flowering genotypes not found in the summer ecotype; (3) the autumn ecotype showed larger genetic diversity than the summer ecotype in long-day treatments; and (4) genetic diversity first became evident in the 14.5-hr photoperiod in the autumn ecotype, and in the 15.0-hr photoperiod in the summer ecotype. These results support the hypothesis based on previous studies that common buckwheat summer ecotypes were derived from autumn ecotypes by adaptation to climate in northern Japan.

Genetic analysis of photoperiod sensitivity associated with difference in ecotype in common buckwheat

“…For each of the 15 landraces, a total of 60 seeds (6 seeds × 2 rows × 5 planters) were sown in soil (Peat Pot V, NPK = 200:1000:200 mg/L; Hokkaido Peat Moss Co., Ltd., Hokkaido, Japan) in plastic planters (19 cm × 59 cm × 16 cm; height × length × width); for KSC2 and BNPL1, 36 seeds (6 seeds × 2 rows × 3 planters) were sown. On the basis of previous studies (Hagiwara et al 1998, Hara and Ohsawa 2013, Michiyama and Hayashi 1998, Michiyama et al 2005, Nagatomo 1961, Onda and Takeuchi 1942, the photoperiod was 15 h, which is a long-day condition that causes the expression of differences in photoperiod sensitivity among landraces. Fluorescent lamps for growing plants (Biolux-A FL40SBR-A; NEC Lighting, Ltd., Tokyo, Japan) were used to control the photoperiod.…”

Important agronomic characteristics of yielding ability in common buckwheat; ecotype and ecological differentiation, preharvest sprouting resistance, shattering resistance, and lodging resistance

“…Iwata et al (2005) showed that genetic diversity tends to be lower in populations with early flowering (summer ecotype), and the genetic structure differs between autumn and summer ecotype populations. Hara and Ohsawa (2013) accurately evaluated photoperiod sensitivity and genetic diversity under a controlled environment. Their results support the hypothesis that summer ecotypes were derived from autumn ecotypes by adaptation to the climate in northern Japan, i.e., adaptation from short-day to long-day cultivation, as outlined in Fig.…”

“…Thus, autumn ecotype cultivars might be more tolerant to preharvest sprouting. The summer ecotype of buckwheat is considered to have derived from the autumn ecotype (Hara and Ohsawa 2013, Iwata et al 2005, Minami and Namai 1986. In double cropping, summer ecotype cultivars could show a greater yield than autumn ecotype cultivars, the yield of which is greatly reduced by long-day conditions Hayashi 1998, Yamazaki 1947).…”

“…Furthermore, excess moisture injury (Sugimoto and Sato 2000), deterioration of soil fertility and poor manuring practice (Hayashi et al 1994, Murayama et al 1998, poor growth due to weed competition (Hatakenaka et al 2015), occurrence of sterile seeds due to lack of the flower-visiting insects (Kasajima et al 2017a), and yield loss due to lodging and shattering (Funatsuki et al 2000) cause low and unstable grain yield. Recently, new breeding objectives for improving yielding ability by increasing preharvest sprouting resistance (Hara et al 2012), reducing shattering loss (Suzuki et al 2012a(Suzuki et al , 2012b; introducing self-compatibility , Breeding Science 70: 39-47 (2020) doi: 10.1270 Mukasa et al 2010); the ecotype (Hara and Ohsawa 2013); and semidwarf (Morishita et al 2015) have been reported. These new approaches would be beneficial for common buckwheat breeding.…”

Do genetic differences in growth thermal reaction norms maintain genetic variation in timing of diapause induction?

“…Genetic variation in the timing of flowering and subsequent seed production is commonly observed in plants (e.g. Bourion et al, 2002;Franks et al, 2007;Hara and Ohsawa, 2013). Similarly, for facultative parthenogenetic animals which typically switch from asexual to sexual reproduction when environmental conditions deteriorate, there is genetic variation in the propensity to produce diapause propagules (P d ) in a given environment, suggesting that genotypes vary in their environmental cue thresholds (e.g.…”