Duration of developmental phases, and dynamics of leaf appearance and tillering, as affected by source and doses of photoperiod insensitivity alleles in wheat under field conditions

Abstract

Variation in photoperiod sensitivity in wheat plays a major role in the crop adaptation to wide agronomic environments. Photoperiod insensitivity is provided by Ppd-Aa, Ppd-B1a and Ppd-D1a alleles. Effects of the genome, doses and source of the particular Ppd-1a alleles on time to anthesis has not been analysed simultaneously in the same experiments, even less under field conditions; and the effects on particular phases rather than on considering only the total time to anthesis and on phyllochron have not been considered for this range of allele combinations. We carried out field experiments during two consecutive growing seasons to assess differences in time to anthesis, in its component phases, in final leaf number, phyllochron and tillering across wheat isogenic lines differing in specific Ppd alleles and homoeoalleles. In addition to confirming that the introgression of Ppd-1a alleles advanced anthesis time (on average by 307, 251 and 191ºC d if there were 3, 2 or 1 insensitivity alleles introgressed, respectively), we found that the variation between photoperiod insensitive genotypes was largely dependent on the varietal source of Ppd-B1a which could be stronger or weaker than Ppd-D1a depending on the donor considered. All components of time to flowering: the particular sub-phases (P<0.001) as well final leaf number (P<0.001) and phyllochron of late-appearing leaves (P<0.05) were sensitive to Ppd-1a alleles, but the strength of particular alleles on particular components was different, so that similar adjustments in time to anthesis could be achieved with different partitioning of developmental time between the considered phases. We also found that although they did not affect phyllochron of the first 7 leaves, that of the leaves appearing later was consistently reduced in lines carrying Ppd-1a. Tillering was sensitive too, but not final number of spikes due to compensations between tillering and tiller mortality.

Dynamics of leaf and spikelet primordia initiation in wheat as affected by Ppd-1a alleles under field conditions

“… Miglietta, 1989 ; Slafer and Rawson, 1994 b ), disregarding whether the length of the phase was determined in thermal time or in phyllochrons. This is because, in agreement with previous studies, the rate of appearance of early leaves seems insensitive to photoperiod ( Slafer and Rawson, 1997 ) and unaffected by photoperiod insensitivity genes ( González et al , 2005 ; Ochagavía et al , 2017 ), although exceptions can be found, at least when grown in controlled conditions ( Pérez-Gianmarco et al , 2018 ). This parallelism is the main reason why the effects of daylength and/or photoperiod insensitivity genes on wheat development can frequently be estimated through their effects on FLN (e.g.…”

“…When plastochrons were quantified based on another developmental trait such as phyllochron, the effects of Ppd-1a alleles on spikelet plastochron calculated in thermal time disappeared. This means that the effects of these alleles on the rate of spikelet initiation actually reflected those on the rate of leaf appearance ( Ochagavía et al , 2017 ), reinforcing the idea that the co-ordination between primordia initiation and leaf appearance is relatively conservative ( Kirby, 1990 ; Miralles et al , 2001 ). In fact, the model proposed by Kirby (1990) for the co-ordination between primordia initiation and the dynamics of leaf appearance predicted that spikelet plastochron was reduced (and the rate of spikelet initiation was increased) with reductions in FLN, and our results agree with that prediction as the introgression of Ppd-1a alleles reduced FLN (see discussion above).…”

“…However, the fact that double ridge occurred well after floral initiation (as recognized several times in the past: Delécolle et al , 1989 ; Kirby, 1990 ) was not eliminated by the introgression of these alleles. The introgression of Ppd-1a alleles did not consistently affect the difference between true floral initiation and double ridge, indicating that differences in the early reproductive phase (from floral initiation to terminal spikelet; Ochagavía et al , 2017 ) caused by these alleles were not mediated by differences in the period between floral initiation and double ridge.…”

“…The last column shows the thermal time to flowering (averaged across seasons) for each NIL. Adapted from Ochagavía et al (2017) , with permission from Elsevier. (This figure is available in colour at JXB online.)…”

Wheat developmental traits as affected by the interaction betweenEps-7Dand temperature under contrasting photoperiods with insensitivePpd-D1background

“…This overall effect is in line with the recognised universal effect of temperature on accelerating developmental processes not only in wheat (Slafer and Rawson, 1994a;John and Megan, 1999); as well as in and other crops (Parent and Tardieu, 2012) and other unrelated organisms (Gillooly et al, 2002). Also the rate of leaf appearance (that was constant for all leaves, as expected when FLN is less than 8; (Ochagavía et al, 2017;Slafer and Rawson, 1997) was positively responsive to temperature; as has been known for a long time (e.g. Miglietta, 1989;Slafer and Rawson, 1997 (Slafer and Rawson, 1994a).…”